by IRFAN ULLAH Department of Chemistry, Gomal University

FORMULATION AND CHARACTERIZATION OF VARIOUS

DRUG CARRIER SYSTEMS AND INVESTIGATING THEIR

ABILITY FOR SOLUBILIZATION OF POORLY WATER

SOLUBLE DRUGS

by

IRFAN ULLAH

Department of Chemistry, Gomal University

Dera Ismail Khan, Pakistan 2013

FORMULATION AND CHARACTERIZATION OF VARIOUS DRUG

CARRIER SYSTEMS AND INVESTIGATING THEIR ABILITY FOR

SOLUBILIZATION OF POORLY WATER SOLUBLE DRUGS

A Dissertation Submitted to Gomal University Dera Ismail Khan in Partial

Fulfillment of the Requirements for the Degree of Doctor of Philosophy

In

Chemistry

by

IRFAN ULLAH A Ph. D scholar

DEPARTMENT OF CHEMISTRY GOMAL UNIVERSITY, DERA ISMAIL KHAN, PAKISTAN

2013

IN THE NAME OF ALLAH

_________________________ THE MOST MERCIFUL

& THE MOST GRACIOUS

Dedicated to My Ever loving Parents, Sweet Brothers, Sisters, my wife and beloved son Muhammad Abdullah.

i

ACKNOWLEDGEMENTS

All glory be to Almighty ALLAH who has created us the most omnipotent and gave me

the courage and zeal to perform this work successfully. All respects for Holy Prophet

HAZRAT MUHAMMAD (peace be upon him) who enlightened our minds to recognize

our creator.

I wish to express my heartiest gratitude to my honorable supervisor Prof. Dr. Musa

Kaleem Baloch (Izaz-i-Fazilat, Tamgha-i-Imtiaz), Professor of Chemistry and Ex-

Dean, Faculty of Sciences, Gomal University, Dera Ismail Khan for his valuable

guidance and helpful discussion about my work into multi aspects over which I can be

proud of forever.

I would like to give my sincere gratitude to Prof. Dr. Azim Khan Khattak, Chairman

Department of Chemistry, Gomal University, Dera Ismail Khan for providing all the

facilities during this work. I am also heartily grateful to Margrette Jayne Lawrence,

professor of Biopharmaceutics, Pharmaceutical Science Division, King’s College

London, United Kingdom, Prof. Dr. Gulrez Fatima Durrani, and Dr. Muhammad

Adeel assistant professor, Department of Chemistry, Gomal University, Dera Ismail

Khan for their cooperation and useful discussion during my whole research work.

I humbly wish the best of luck to all my Dear Class Fellows, for their kind deed or

thoughts for me. I also appreciate the role of the office, library and laboratory staff in our

achievements. Special thanks are reserved for my parents and other members of my

family for their love, prayers, patience, nice and encouraging attitude throughout my life.

The financial support provided by HEC, in terms of Indigenous Scholarships and IRSIP

Fellowship is highly acknowledged.

Irfan Ullah

ii

CONTENTS

Chapter No PARTICULARS Page No

Acknowledgement i

Table of Contents ii

List of Tables v

List of Figures ix

Abstract

xiv

1 INTRODUCTION 1-6

1.1 Drugs and their classification 1

1.2 Carrier used in drugs delivery 3

1.3 AIMS AND OBJECTIVES 7

2 LITERATURE REVIEW 8-16

3

EXPERIMENTAL 17-29

3.1 Materials 17-24

3.1.1 Hydrotropes 17

3.1.2 Surfactants 18

3.1.3 Menthol 22

3.1.4 Drugs 22

3.1.5 Oils 24

3.2 Methods 25-29

3.2.1 Sample preparation 25

3.2.2 Phase diagram 25

iii

3.2.3 pH measurement 26

3.2.4 Estimation of minimum hydrotropic concentration 26

3.2.5 Estimation of critical micelles concentration 26

3.2.6 Centrifugation 27

3.2.7 Measurement of solubility 27

3.2.8 Differential scanning calorimetry 28

3.2.9 Laser light scattering measurement 28

3.2.10 Refractive index measurement 29

4 RESULTS AND DISCUSSION 30-135

4.1 Estimation of minimum hydrotropic concentration 30

4.2 Solubility of drugs in water 33

4.3 Solubility of drugs in buffer solution 33

4.4 Effect of hydrotropes over the solubility of drugs 34

4.5 Estimation of critical micelles concentration of surfactants 58

4.6 Effect of surfactants over the solubility of drugs 68

4.7 Hydrodynamic radius of micelles loaded with drugs 81

4.8 Effect of hydrotropes on critical micelles concentration of

DDAPS

89

4.9 Effect of hydrotropes on solubility of drugs in DDAPS 96

4.10 Aggregation number of DDAPS/NaSal and DDAPS/NaBen

106

4.11 Hydrodynamic radius of DDAPS/NaSal and DDAPS/NaBen 109

iv

mixture

4.12 Effect of addition of butanol on solubility of drugs 111

4.13 Solubility of drugs in oil-in-water microemulsion 112

4.14 Aggregation number of DDAPS, DDAPS/butanol and

microemulsion

113

4.15 Hydrodynamic radius of DDAPS/butanol mixture and

microemulsions

117

4.16 Microemulsion having Menthol and/or Eutectic mixture as an oil 120

4.17 Aggregation number of microemulsion having Menthol and

Eutectic mixture as oil

127

4.18 Hydrodynamic radius of microemulsion having Menthol and

Eutectic mixture as oil

128

4.19 Refractive index of various systems 130

Conclusion 136-137

References 138-153

v

S.No Title of Table Page No.

1 Biopharmaceutical classification of drugs developed by Amidon and

his coworkers

2

2 Techniques employed for the preparation of carrier systems 6

3 Minimum hydrotropic concentration (MHC) calculated from Figure

1 and the one available in the literature

32

4 Solubility of drugs in water; measured at 25oC 33

5 Solubility of drugs at various pH 34

6 Maximum hydrotropic concentration calculated from Figures 2-17 51

7 Various parameters of Meloxicam in aqueous solution of

hydrotropes; measured at 25oC.

54

8 Various parameters of Celecoxib in aqueous solution of hydrotropes

measured at 25oC.

55

9 Various thermodynamic parameters of Lidocaine in aqueous solution

of hydrotropes; measured at 25oC.

56

10 Various thermodynamic parameters of Ibuprofen in aqueous solution

of hydrotropes; measured at 25oC.

57

11 CMC of the surfactants determined from the surface tension of their

aqueous solution and the one available in the literature. The

aggregation numbers are one obtained from the literature.

66

12 CMC of the surfactants determined from the surface tension of their 67

vi

aqueous solution and the one available in the literature. The

aggregation numbers are one obtained from the literature.

13 Various parameters of Meloxicam in aqueous solution of surfactants;

measured at 25oC.

77

14 Various parameters of Celecoxib in aqueous solution of surfactants;

measured at 25oC.

78

15 Various parameters of Ibuprofen in aqueous solution of surfactants

measured at 25oC.

79

16 Various parameters of Lidocaine in aqueous solution of surfactants;

measured at 25oC.

80

17 Hydrodynamic radius of pure and drug saturated micelles of various

surfactants; measured at 25oC

88

18 Surface tension (mN.m-1) of DDAPS in the presence of NaSal

measured at 25oC

90

19 Surface tension (mN.m-1) of DDAPS in the presence of sodium

benzoate; measured at 25oC

92

20 Various parameters of drugs calculated in the presence of DDAPS at

25oC

103

21 Various parameters of drugs calculated in the presence of

DDAPS/NaSal at 25oC

104

22 Various parameters of drugs calculated in the presence of 105

vii

DDAPS/NaBen at 25oC

23 Aggregation number of DDAPS micelles formed in aqueous solution

of 0.4 molar NaSal; measured at 25oC

107

24 Aggregation number of DDAPS micelles formed in aqueous solution

of 0.4 molar NaBen; measured at 25oC

108

25 Effect of addition of NaSal (0.4 mol.L-1)on hydrodynamic radius of

DDAPS; measured at 25oC

109

26 Effect of addition of NaBen (0.4 mol.L-1)on hydrodynamic radius of

DDAPS measured in water/butanol mixture at 25oC

110

27 Effect of addition of butanol to water on solubility of drugs in 0.5

mol.L-1 DDAPS at 25oC

111

28 Effect of addition of 2% (v/v) hydrocarbons over the apparent

solubility of drugs in DDAPS/butanol (0.5 mol.L-1/1.2 mol.L-1)

mixture at 25oC

112

29 Aggregation numbers of DDAPS Micelles in water; measured at

25oC

114

30 Effect of addition of butanol on aggregation number of 0.5 mol.L-1


115

31 Effect of addition of 2% (v/v) hydrocarbons over the aggregation

number of DDAPS/butanol (0.5mol.L-1/1.2mol.L-1) mixture;

measured at 25oC

116

32 Hydrodynamic radius of blank and drugs saturated DDAPS Micelles 117

viii

measured at 25oC

33 Effect of addition of butanol on hydrodynamic radius of drug

saturated (0.5mol.-l) DDAPS at 25 oC

118

34 Effect of addition of 2% (v/v) hydrocarbons over the hydrodynamic

radius of DDAPS/butanol (0.5mol.L-1/1.2mol.L-1)/drug systems at

25oC

119

35 Composition of microemulsions having the capacity of sustaining

maximum oil

125

36 Composition of oil in water microemulsions obtained from phase

diagrams and can be diluted to a very low surfactant concentration

126

37 Aggregation number of microemulsions measured at 25oC 127

38 Hydrodynamic radius of microemulsion measured at 25oC 129

39 Refractive index of DDAPS micelles and its microemulsion

measured at 25oC

130

40 Refractive index of DTAB micelles and its microemulsion measured

at 25oC

131

41 Refractive index of SDS micelles and its microemulsion measured at

25oC

132

ix

S.No List of Figures Page.No

1 Surface tension as a function of hydrotrope concentration;

measured at 25oC

31

2 Solubility of Meloxicam in aqueous solution of sodium benzoate

as a function of concentration and temperature

35

3 Solubility of Meloxicam in aqueous solution of sodium

salicylate as a function of concentration and temperature

36

4 Solubility of Meloxicam in aqueous solution of sodium p-

toluene sulfonate solution as a function of concentration and

temperature

37

5 Solubility of Meloxicam in aqueous solution of sodium xylene

sulfonate as a function of concentration and temperatures

38

6 Solubility of Celecoxib in aqueous solution of sodium benzoate

as a function of concentration and temperatures

39

7 Solubility of Celecoxib in aqueous solution of sodium salicylate


41

8 Solubility of Celecoxib in aqueous solution of sodium p-toluene


41

9 Solubility of Celecoxib in aqueous solution of sodium xylene


42

10 Solubility of Lidocaine in aqueous solution of sodium benzoate


43

x

11 Solubility of Lidocaine in aqueous solution of sodium salicylate


44

12 Solubility of Lidocaine in aqueous solution of sodium p-toluene


45

13 Solubility of Lidocaine in aqueous solution of sodium xylene


46

14 Solubility of Ibuprofen in aqueous solution of sodium benzoate


47

15 Solubility of Ibuprofen in aqueous solution of sodium salicylate


48

16 Solubility of Ibuprofen in aqueous solution of sodium p- toluene


49

17 Solubility of Ibuprofen in aqueous solution of sodium xylene


50

18 Surface tension of aqueous solution of Tween 20 as a function of

its concentration; measured at 25oC

59

19 Surface tension of aqueous solution of Tween 80 as a function of

its concentration; measured at 25oC

60

20 Surface tension of aqueous solution of Triton X-100 as a

function of its concentration; measured at 25oC

61

21 Surface tension of aqueous solution of Triton X-114 as a 62

xi

function of its concentration; measured at 25oC

22 Surface tension of aqueous solution of surfactants as a function

of their concentration and measured at 25oC

63

23 Surface tension of aqueous solution of Brij 30 as a function of its

concentration; measured at 25oC

64

24 Surface tension of aqueous solution of Brij 35 as a function of its


65

25 Solubility of Meloxicam in aqueous solution of nonionic


70

26 Solubility of Celecoxib in aqueous solution of nonionic


71

27 Solubility of Lidocaine in aqueous solution of nonionic


72

28 Solubility of Lidocaine in aqueous solution of various

surfactants; measured at 25oC.

73

29 Solubility of Ibuprofen in aqueous solution of surfactants;

measured at 25oC.

74

30 Autocorrelation function of Tween 20 micelles 81

31 Autocorrelation function of Tween 80 micelles 82

32 Autocorrelation function of Brij 30 micelles 83

xii

33 Autocorrelation function of Brij 35 micelles 84

34 Autocorrelation function of Triton X-100 micelles 85

35 Autocorrelation function of Triton X-114 micelles 86

36 Autocorrelation function of DDAO micelles. 87

37 Variation in surface tension of DDAPS by the addition of

sodium salicylate as a function of DDAPS concentration;

measured at 25oC

91

38 Variation in surface tension of DDAPS by the addition of

sodium benzoate; measured at 25oC

93

39 Effect of sodium salicylate on CMC of DDAPS measured at

25oC

94

40 Effect of sodium benzoate on CMC of DDAPS measured at

25oC

95

41 Solubility of Lidocaine in aqueous solution of DDAPS/

(0.4mol.L-1) NaSal mixture; measured at 25oC

97

42 Solubility of Meloxicam in aqueous solution of DDAPS/

(0.4mol.L-1) NaSal mixture; measured at 25oC

98

43 Solubility of Celecoxib in aqueous solution of DDAPS/

(0.4mol.L-1) NaSal mixture at 25oC

99

44 Solubility of Lidocaine in aqueous solution of DDAPS/

(0.4mol.L-1) NaBen mixture; measured at 25oC

100

45 Solubility of Meloxicam in aqueous solution of 101

xiii

DDAPS/(0.4mol.L-1) NaBen mixture; measured at 25oC

46 Solubility of Celecoxib in aqueous solution of

DDAPS/(0.4mol.L-1) NaBen mixture; measured at 25oC

102

47 DSC curve of Lidocaine/Menthol mixture 120

48 Phase diagrams of microemulsions stabilized by DDAPS at 25oC 122

49 Phase diagrams of microemulsion stabilized by DTAB at 25oC 123

50 Phase diagrams of microemulsion stabilized by SDS at 25oC 124

51 Refractive index of DDAPS micelles and its microemulsion;

measured at 25oC

133

52 Refractive index of DTAB micelles and its microemulsion;

measured at 25oC

134

53 Refractive index of SDS micelles and its microemulsion;

measured at 25oC

135

xiv

ABSTRACT

Poor aqueous solubilities of drug candidates limit their bioavailability. A number of

delivery systems are in use to enhance the bioavailability of the drugs with poor solubility

in water. The self-assemblies of hydrotropes, surfactants and oil/water micro emulsions

may provide a means of enhancing solubility and enhance bioavailability of drugs.

Although these drugs delivery systems are in use but the mechanism through which these

delivery systems solubilize the drugs needs detail investigations. The objective of the

current dissertation was to provide the understanding of the mechanism through which

simple aggregates of hydrotropes, micelle of surfactants and oil in water microemulsions

solubilize the drugs. For the purpose, apparent solubility of drugs namely, Meloxicam,

Celecoxib, Ibuprofen and Lidocaine was determined in aqueous solution of hydrotropes,

surfactants, surfactant/hydrotrope, surfactants/butanol mixtures and in oil/ water

microemulsions. These mediums were tested for their ability to enhance the aqueous

solubility of these water insoluble drugs. The results obtained for molar solubilization

ratio (MSR), partition co-efficient (KM) of the investigated drugs concluded that these

were lower in hydrotropes as compared to the one obtained in other stated systems.

Among the hydrotropes, sodium benzoate showed highest (0.006- 0.0107), whereas

sodium p-toluene sulfonate (0.0014- 0.0052) the lowest MSR values. The negative values

obtained for ∆Go illustrated the spontaneous mixing of these drugs in all the investigated

systems. The CMC, HLB, oxyethylene units and aggregation number of surfactants along

with molecular mass of the drug, polarity of the drug and the group attached to them

showed a great impact over the solubility of two model drugs, Meloxicam and Celecoxib

in nonionic surfactants including Tween 20, Tween 80, Brij 30, Brij 35, Triton X-100,

xv

and Triton X-114. It was noted that the surfactants with high aggregation number

solubilized higher amount of drugs and had higher value of MSR than others. The

solubility was enhanced with the increase in number of oxyethylene units in a surfactant.

The solubility was also increased with the increase in number of carbon atoms in alkyl

chain of surfactants used. Similar results were observed when Lidocaine was solubilized

in ionic, nonionic and zwitterionic surfactants. Among the nonionic, N,N,

Dimethyledodecyle amine-N-Oxide (DDAO) whereas among ionic and zwitterionic

surfactants, N,N, Dimethyldodecyle- amonio propane-sulfonate (DDAPS) surfactants

showed higher ability to solubilize the model drug, Lidocaine. The addition of

hydrotropes and/or butanol to aqueous solution of DDAPS showed a noticeable increase

in solubility of all the investigated drugs. In case of oil/ water microemulsion, the

increase in molecular mass of oil in a homologous series increased the solubility of drugs.

It was also noticed that microemulsions had highest ability to solubilize the drugs among

all the investigated systems. The results obtained by light scattering revealed that the

addition of drugs does not increase the aggregation number and hydrodynamic radius of

the surfactants micelles. However, both the aggregation number and size was increased

by the addition of butanol and hydrotropes. The addition of hydrocarbon to the

DDAPS/butanol mixture resulted a decrease in micellar size as well as the aggregation

number. Similar observations were also made for aggregation number and hydrodynamic

radius in case of Menthol or Eutectic mixtures of Lidocaine/Menthol used as an oil phase.

All these observations concluded that the drugs are solubilized in inner core of

micelles/aggregates of the surfactants/hydrotropes. However in case of oil/water

microemulsions these were solubilized only in oil phase of microemulsions.

1

1. INTRODUCTION

1.1. Drugs and their classification

Drugs are the substances that change the bodily function on absorption into the body of

living organism. In pharmacology, a drug is a substance which may have medicinal and

intoxicating, performance when taken or put into a human body. Drugs are mostly

recommended for a limited time, or on a regular basis for chronic disorders. They can be

administered via different routes like, Oral, by Rectal, Topical, Parenteral, Respiratory,

Nasal, Eye and Ear. Therefore, in almost every methodology; vehicles are required or

have to be solubilized before administration. Further to it the drugs having low solubility

cause various problems with respect to their in vivo absorption. Recognizing the

importance of solubility, Amidon and his coworkers classified the drugs based over their

solubility which is also known as Biopharmaceutical classification system (Table 1) [1].

Recent advances in drug discovery (combinatorial chemistry and high through-put

screening) led to the identification of large numbers of compounds with good therapeutic

potential, however most of these compounds have extremely poor aqueous solubility and

fall into class II or IV [2-4].

2

Table 1 Biopharmaceutical classification of drugs developed by Amidon and his

coworkers.

Class Solubility Permeability Description

I High High Drugs having higher absorption than excretion.

II Low High These drugs have limited Bioavailability by their

solvation rate. A correlation can be found between in

vivo bioavailability and in vitro solvation.

III High Low Although absorption of such drug is limited by the

permeation rate but its solvation is very fast.

IV Low Low These drugs have poor bioavailability. They are

poorly absorbed over the intestinal mucosa and a

high variability is expected.

3

1.2.Carrier used in drugs delivery

It is estimated that more than 40% of the drug candidates (pharmaceutically active

ingredients) are discarded due to their poor solubility, and hence low and variable

bioavailability. Therefore, over the last two decades, lot of research efforts have been

focused over the development or improvement of the drug carriers which are also known

as delivery systems, specifically for the challenging drug candidates, belonging to classes

II and IV of the biopharmaceutical classification system [5-7].

In order to overcome the problems of low aqueous solubility of drugs and drug

candidates, new delivery systems are introduced. It has been concluded that for drug

candidates exhibiting highly lipophilic tendencies, would be beneficial to deliver these to

the patient in the pre-dissolved state and the solvent which can be used for the purpose be

either a lipid solution, a lipid emulsion, a microemulsion (ME), or a self-emulsifying (or

micro-emulsifying) drug delivery system (S(M)EDDS) [8-11]. In this way the energy

associated with a solid–liquid phase transition will be reduced that would be otherwise

required for the dissolution of the drug after administration to the patient. Therefore a

number of (carrier) systems have been developed which can solubilized the drugs. A

carrier system required for the proper delivery of the drugs is described as a tool desired

for enhancing the therapeutic effectiveness of a bioactive agent [12-13]. Generally,

nonreactive matrixes are used as a carrier system for the delivery and targeting of drugs

inside or outside the body and protect its load from attack of oxygen, light and/or

enzymes which can destruct it and also prevent the drugs to react with other reactive

components [14-16]. Polymers, biopolymers, lipids and surfactant-based systems and oils

or their mixture can be used as carrier systems. The most common systems used as drug

4

carriers are micro-spheres, nano-spheres, liposomes, nano-liposomes and vesicular

phosphor-lipid gels (VPG), archaeo-somes, and nio-somes [17-25]. Micelles and nano-

particles are the examples of mixed carrier systems that can be prepared from

polymer/surfactant and/or polymer/lipid conjugates mixtures [14, 25]. The particle size of

carrier systems may vary from micrometric to nano-metric size and should be kept

constant during their preparation and application. The key parameters that play a major

role in designing and formulation of carrier systems are the methods of preparation and

loading of drugs, their particle size distribution and firmness and degradation properties

of the bioactive-carrier complex along with the release kinetics of the loaded drugs [26].

The preferred carrier systems are the one that is biodegradable and bio absorbable, as

these can be degraded inside the body due to hydrolytic or enzymatic actions, without

creating any toxic material. A number of techniques (based over lab scale and large scale

applications) can be employed for the formulation of the carrier systems and loading of

bio active materials. Table 2 comprises some of the examples of such methodologies and

the carriers so formed [10, 20, 23, 27-34]. Nevertheless, for the entrapment of sensitive

substances, most of these methods are not suitable as they cannot sustain against

mechanical stresses, high-shear homogenization, sonication, high pressures etc., or

change in pH during the preparation [35]. Moreover these methods of preparation use the

injurious low boiling solvents like acetone, ether, chloroform, to dissolve or solubilize the

constituents [36] and if these solvents are remained in the final product as a residue then

they may not only modify the chemical structure of the entrapped material but also

affects the stability of the carrier system and add toxicity to the product [37]. These

residual solvents which are organic volatile impurities are dangerous to human and

5

animal health and to the environment. Further to it such compounds do not have any

therapeutic benefits [38]. Certainly, it is not an easy job to remove these solvents up to

zero level and the process is also very expensive. Therefore such preparations are not

only unstable but also very costly and dangerous; hence can be concluded as not suitable

for the formulations [39]. Keeping in view above mentioned factors, we have tried to

enhance the solubility of various drugs in water using hydrotropes and/or surfactants, oils

and to solubilize the drugs in their micelles or microemulsions, as the case may be or by

preparing eutectic mixture of Menthol with drugs. The efforts have also been made to

explore the forces involved for the enhancement of solubility of drugs and to propose the

mechanism of solubilization.

6

Table 2 Techniques employed for the preparation of carrier systems.

Preparation method Carrier system References

Thin film hydration method Niosomes/liposomes [20, 23, 27]

Sonication Nanoliposomes/archaeosomes [10]

Heating method Nanoliposomes/liposomes/archaeosomes

/VPG

[10, 28-30]

Reverse-phase evaporation Liposomes/archaeosomes [10, 30]

Ether-injection technique Liposomes [10, 30]

High-pressure

homogenization

VPG* [31]

Precipitation

polymerization

Nanoparticles [32]

Emulsification- diffusion

method

Nanoparticles [32]

Emulsion-solvent

evaporation technique

Microspheres [33-34]

*Vesicular phospholipid gels

7

1.3. AIMS AND OBJECTIVES

Keeping in view the poor-aqueous solubility and high hydrophobicity of Meloxicam,

Celecoxib, Ibuprofen and local anesthetic Lidocaine were selected to enhance their

aqueous solubility and to increase their bioavailability and to identify a best system

which can dissolve the drug up to large extent and show minimum health risks. For the

purpose, the following carrier aqueous systems were investigated:

1. Various hydrotropes/water system

a. Effect of concentration of hydrotropes over solubility

b. Effect of temperature over solubility

2. Aqueous solution of surfactants

3. Hydrotropes/ surfactants/water

4. Butanol/ surfactant / water system

5. Oil/water microemulsions

a. Hydrocarbon as oil

b. Menthol/Lidocaine eutectic mixture

6. Menthol/water/ surfactant system

The solubility of the drug was investigated using UV/Vis spectroscopy whereas the

CMC and MHC were obtained using surface tension measurement. The

hydrodynamic radius and aggregation number of the micelles/microemulsions was

measured using dynamic light scattering techniques. It was tried to identify the best

system for the delivery of these drugs based over the data obtained.

.

8

2. LITERATURE REVIEW

NSAIDs, the nonsteroidal anti-inflammatory drugs are a class of compounds that poses

antipyretic, analgesic, and anti-inflammatory effects which lessen the pain as these

compounds interacting with the cyclooxygenase (COX) enzyme which manufactures

prost-aglandins, producing inflammation [40]. They reduce or eliminating the pain by

preventing the production of prost-aglandins, [41]. In osteo-arthritis of the knee, the

NSAIDs are good enough in reducing the instant pain than placebo but for this condition

the prolong intake of these drugs is not supportive. Limited use is recommended due to

serious side effects that are related with oral NSAIDs [42]. For the treatment of acute

inflammation in joints, the Cyclo-oxygenase-2 (COX 2) inhibitors can be employed as

these drugs are as effective as that of NSAIDs in relieving pain [43], they decrease the

arthritis like NSAIDs but without the gastro-intestinal side effects that is associated with

traditional NSAIDs. The devastating effects of NSAIDs can be avoided by their Intra-

articular administration which is alternative to their delivery administration. For the

maintenance of therapeutic intra-articular levels, the frequent injections of NSAIDs

would be required. The sustained drug delivery devices offers an excellent alternative to

multiple intra-articular injections and produced good results [44], by local administration

of a new slow release NSAID-carrier formulation, the improved NSAIDs efficacy and

relief of adverse effects can be achieved. Lin et al., prepared water soluble diclofenac

sodium loaded microshere by using three low-molecular weight poly-esters, poly (L-

lactic acid), co-poly (lactic acid/glycolic acid), and (delta-valerolactone) i.e. (PLA),

(PLGA) and poly (PV).The oil/oil emulsification solvent evaporation method was

employed for preparation of microshere. Their dissolution behaviours, degradation,

9

physicochemical and micromeritic properties were determined in vitro. By the oil/oil

emulsification solvent evaporation technique, high encapsulation efficiency and

improved monodispersity was attained depending on the amount of drug loaded. The

powder x-ray diffractometry and differential scanning calorimetry revealed the measured

loss of organic solvent from the system throughout micro-encapsulation which was

responsible for the modification of the crystal structure of drug and polyester in the

micro-spheres. In phosphate buffer solution pH 7.4, the in vitro degradation showed

first-order kinetics, and ranked in the order of PV< PLA < PLGA micro-spheres. In all

micro-spheres, the first-order release rate was also found and ranked in the order of PV<

PLA < PLGA microspheres after an initial drug burst [45]. Tuncay et al., formulated the

diclofenac sodium (DS) for intra-articular administration and studied its controlled-

release. They characterized in vitro for release characteristics, drug loading, particle size,

morphology of the surface and yield. Radioactive isotopes were used for the

demonstration of arthritic injuries by gamma scinti-graphy. The evaluation of post-

therapy of arthritic lesions in rabbits established no difference compared to control

groups, the group treated with PLGA (50:50) (Mw 34 000 g.mol-1) DS microspheres,

[46]. Todd et al., likened the effectiveness of Diclofenac to that of the several fresh and

already developed NSAIDs, in a number of clinical trials and found it equivalent.

Diclofenac has a fast onset and long duration of action when used as an analgesic. When

administered intramuscularly in renal and biliary colic it was found to be analogous to,

and superior to, many narcotic and spasmolytic combinations. Establishing safety profile

with diclofenac, widespread medical knowledge has been added. It is well accepted

associated with other NSAIDs and rarely produces gastrointestinal ulceration or other

10

stern side effects. Thus, in the cure of severe and long-lasting aching and provocative

conditions, diclofenac can be considered as one of the few NSAIDs of 'first choice' [47].

Savanna et al., employed emulsification/crosslinking method to manufacture

microspheres loaded with drug. They used various techniques in order to characterize

these microshere. They studied in vitro release and characterized them by size

distribution, Fourier transform infrared (FTIR) spectroscopy, drug loading, differential

scanning calorimetry (DSC), scanning electron microscopy (SEM), gas chromatography

and X-ray diffraction (XRD). They studied in vivo by testing targeting efficiency of

microspheres in rabbits [48]. Thakkar et al., prepared chitosan micro-spheres by

emulsification cross-linking method and heat linked method and also associated the

features of these micro-spheres of chitosan. Two dissimilar cross-linking agents:

HCOOH and glutaraldehyde. SEM was employed for the characterization of these

microspheres for their ability to load drugs, particle size distribution, and release of drug

in-vitro and morphology of surface. The heat-cross-linked micro-spheres has the lower

entrapment efficiency than that of glutar-aldehyde and HCOOH cross-linked micro-

spheres (P <0.05). The heat cross-linked microspheres showed better performance in

releasing the drug as cpmapre to one cross-linked using glutaraldehyde and exhibited

measured release than one, cross-linked with HCOOH when these were studied In-vitro

for the release of drug [49]. Elron-Gross et al., developed Diclofenac formulation for

slow-release by local administration to enhance its efficacy and lessen the contrary effects

and for the purpose they employed micro-particles prepared from collagen-lipid

conjugates as carriers. A high-efficiency drug encapsulation (85%) was displayed by

collagomers that were stable in simulated synovial fluid and presented slow drug release

11

(τ 1/2 = 11days) as well as high affinity to target cells (Kd = 2.6 nM collagen) [50].

Bhardwaj et al., studied the release of dexamethasone from non-extruded and small

sonicated lipo-somes and evaluated the physicochemical properties of hydrophobic drug.

It was noted that the increase in lipid chain length decreases the encapsulation of

dexamethasone. The decrease in enthalpy and increase in the peak width of the main

transition indicated the destabilization of the liposome membranes by Dexamethasone.

DSC analysis showed the heterogeneously distribution of dexamethasone and cholesterol

in the non-extruded liposomes. The drug encapsulation (approximately 50%) and

diameter (DSPC > DPPC > DMPC) of lipo-some were reduced by sonication and

extrusion. As cholesterol and dexamethasone resemble structurally, hence its

incorporation in both extruded and non-extruded DMPC liposomes decreased the drug

encapsulation. A Phase transition was observed when dexamethasone and cholesterol

were loaded in combination in the same DMPC liposomes. Dexamethasone showed

slower release from non-extruded lipo-somes than from extruded lipo-somes. Similarly

liposomes of high phase transition lipid DSPC showed slowest release as compare to

DMPC liposomes and incorporation of cholesterol did not decrease release from DMPC

liposomes. These results indicated that incorporation of hydrophobic drug dexamethasone

affected the properties of lipo-somes [51]. Tsotas et al., studied dexamethasone

formulated in liposome and other gluco-corticoids. However, these liposomes had

variable physicochemical properties [52]. Swarnlata et al., formulated transdermal

delivery of Lidocaine by employing two different kinds of polymer patches; one

comprises on combination of ethyl cellulose (EC) and hydroxyl-propyl-methyl-cellulose

(HPMC) and second with polyvinyl alcohol (PVA) alone. The polymer solution of

12

HPMC 10% and EC 10% was prepared by mixing Methanol and chloroform in the ration

of 1:1. These two solutions were mixed together in various combinations. PVA matrix

patches were prepared by mixing Polymer (5, 10 and 15%) concentration in water with

glycerin (0.5%) as plasticizer [53]. DentiPatch, Lidocaine patch were Prepared by Noven

Parmaceuticals, Inc. These systems can be applied topically to the oral cavity and

contained Lidocaine a local anesthetic agent. For local anesthesia these system were

applied to the buccal mucosa for the release of Lidocaine, which prevents the ionic fluxes

essential for the commencement and transmission of impulses and hence stabilizes the

neuronal membrane thereby effecting local anesthetic action [54]. Dollo et al.,

investigated the in vitro release of Lidocaine from tube cuffs filled which contained

Lidocaine in various forms i.e alkalinized Lidocaine hydrochloride, base form, or

hydrochloride form. The endotracheal tube cuff filled with Lidocaine solution were

compared with the cuffs inflated only with air for their pharmacokinetic and pharma-

codynamic effects. A preliminary pilot clinical study in anesthesia was carried out for

spine surgery in smoker patients and it was noticed that the Lidocaine in neutral base

hydrophobic form presented greater rate (65.161% released after 6 h) of diffusion as

compared to hydrochloride in charged form for which only a infusion phenomenon was

taken place with reference to only 1% of the total drug, when their in vitro experiment

was carried out. In present study minute (20–40 mg vs. 200–500 mg) quantity of the

Alkalized form of Lidocaine hydrochloride was used as compare to previous available

literature value, and allowed no lag time for dispersion. For Lidocaine such a system

could offer a controlled release pool to adjacent tracheal tissue [55]. Morales, developed

metered-dose aerosol delivery system for the delivery of local anesthetic mixture of

13

Lidocaine and Prilocaine in base form without organic solvents. In order to investigate

the safety and efficiency of this unique delivery system, an open labeled pilot study was

made for topical local anesthetic to the glans penis planned at increasing the time of the

IVELT in patients who reported for having premature ejaculation. The aerosol contained

Lidocaine (7.5 mg) and prilocaine (2.5 mg), in base form, per actuation. [56]. Zhang et

al., studied prolonged, local analgesic action by investigating the rapid (~1 min)

Lidocaine delivery from coated micro needles by means of 3M’s compact micro-

structured transdermal system. Formulations comprising Lidocaine and dextran were

developed for uniform and thick coating on the micro needles. High performance liquid

chromatography (HPLC) was employed for the determination of the amount of Lidocaine

coated onto the microneedles. The Lidocaine-coated microneedles were introduced into

inland swine in order to evaluate drug delivery and dermal pharmacokinetics. Finally

HPLC and mass spectrometry (LC-MS) was used for determination of Lidocaine in the

Skin punch biopsies that were collected for analysis. The rate of dissolution of Lidocaine

was much more rapidly from the microneedles as compared to that of EMLA (Eutectic

Mixture of Local Anesthetic) cream) [57]. Ammon, et al., prepared microemulsion based

system for the delivery of lidocaine. This nano sized dispersion system for topical and

transdermal administration of drug and cosmetic agents has shown most promising

results for the hydrophilic and lipophilic molecules [58]. Singh et al., investigated the

development and characterization of microcapsule for the administration of Flurbiprofen

through colon [59]. Najm-ud-din et al., formulated an oral colon specific, pulsatile device

containing Flurbiprofen and tried to achieve time and/or site specific release of drug

loaded. The elementary design contained eudragit microsphere of Flurbiprofen packed in

14

an unsolvable hard gelatin capsule body sealed with a hydrogel plug. The colon-specific

release was achieved by enteric coating the whole device and overcoming the unevenness

in gastric emptying time. By using 1:1:2 of Drug: Eudragit L-100: Eudragit S-100

microsphere of Flurbiprofen was prepared. For maintaining a suitable lag period different

hydrogel polymers were used as plugs, and their amount thus used controlled release of

drug. Controlled release of Flurbiprofen from microsphere can be achieved by enhancing

the amount of hydrophilic polymer used [60]. Bhaskar et al., used Quasi-emulsion

solvent diffusion method for the preparation of micro-sponges containing Flurbiprofen

and Eudragit RS 100 and tried to achieve formulation of Flurbiprofen (FLB) micro-

sponges for colon specific drug delivery. Using entrapment method Flurbiprofen was

captured into a commercial Micro-sponge 5640 system. They investigated the effects of

various parameters including inner phase solvent amount, stirrer type, and drug: polymer

ratio, time and speed of stirring on the physical properties of micro-sponges. Detailed

study of particle size, surface morphology, thermal behaviours and pore structure of

micro-sponges were made by employing the methods of compression coating and pore

plugging of micro-sponges with pectin: hydroxylpropylmethyl cellulose (HPMC)

mixture, the colon specific formulations were prepared followed by tableting. All the

formulations were studied in vitro and the results were kinetically and statistically

evaluated. The shapes of micro-sponges were spherical having high porosity values (61–

72%) with diameter, between 30.7 and 94.5 μm. The pore shapes of micro-sponges were

tubular holes. By deforming the sponge-like structure of micro-sponges to the plastic, the

mechanically strong tablets can be prepared for colon specific drug delivery [61]. Orlu et

al., devolved the colon specific drug delivery system for the Flurbiprofen micro-sponges

15

and characterized it using different techniques [62]. Verma et al., investigated delivery

systems developed by using HPMC Matrices containing Flurbiprofen for the transdermal

delivery and made its in Vitro and in Vivo Evaluation [63]. Chauhan et al., developed

delivery system for the delivery of Flurbiprofen this system comprised on controlled

porosity osmotic pump [64]. Singh et al., investigated that how to increase the

transdermal delivery of Ketoprofen by using bio-adhesive gels [65]. El-Kamel et al.,

developed the Ketoprofen floating oral delivery system and characterized it by employing

routinely used techniques [66]. Philip et al., developed drug delivery system for

Ketoprofen in order to achieve osmotic, controlled and level an in vitro in vivo

correlation [67]. Saber et al., developed the formulation using polyelectrolyte complex as

a matrix former for Ketoprofen sustained release tablet and investigated the effect of

variables affecting the formulation [68]. Dhamankar, et al., formulated the oil in water

microemulsion for the delivery of ketoprofen and improving its transdermal absorption

[69]. Ganesh et al., formulated the floating drug delivery system of Ketoprofen and made

its evaluation using different techniques that are normally employed for characterization

[70]. Oliveira, investigated the Mefenamic acid performance with pectin [71]. Tang, et

al., developed the strategy for enhancing the oral delivery of poorly water soluble drugs

by employing self-emulsifying drug delivery systems [72]. Sevgi, et al,. formulated

micro-particles of Mefenamic acid and investigated it’s in vitro release, and in situ

studies in rats [73]. Havaldar et al., developed the techniques for the estimation of

Cetirizine Dihydro-chloride, Acetyl Salicylic Acid, Paracetamol and Mefenamic in the

pharmaceutical dosage form [74]. Roy et al., formulated the chitosan microsphere of

Mefenamic acid and investigated the effect of method of preparation on them [75].

16

Ramanathan, et al., formulated the floating tablets of Mefenamic acid using with

different grades of HPMC and investigated its release profiles [76]. Calija , et al.,

developed drug delivery system of Naproxen using Alginate–Chitosan micro-particles

and investigated in vitro release behavior [77]. Sarfraz et al., developed the sustained

release matrix system composed of cellulose derivatives and investigated Naproxen

release from them [78]. Karasulu et al,. formulated the microemulsion systems for

topical delivery of Naproxen and evaluate its physico-chemical properties [79].

Sutradhar et al., formulated the Naproxen matrix tablets based on hydrophilic and

hydrophobic polymer and investigated the formulation by comparing it’s in vitro release

Profile [80].

17

3. EXPERIMENTAL

3.1. Materials

3.1.1. Hydrotropes

a) Sodium salicylate

It was purchased from Sigma (UK), its product No. was S3007 and CAS No was 54-21-7.

Its Molecular Formula was C7H5NaO3, and Molar mass was 160.1 g.mol-1. Whereas its

structural formula is given below:

b) Sodium benzoate,

It was purchased from Fluka (UK), its product No was 71300 and CAS No was 532-32-1.

Its Molecular mass was 144.10 g.mol-1 and Molecular Formula was C6H5COONa.

Whereas its structural formula is as follows:

c) Sodium p-toluene sulfonate

It was obtained from Aldrich (UK), its Product No. was 152536 and CAS No was 657-

84-1. Its Molecular mass was 194.18 g.mol-1 and Molecular formula was C7H7NaO3S.

Whereas its structural formula is given below:

18

d) Sodium xylene sulfonate,

It was purchased from Aldrich (UK), its Product No was 243078 and CAS No was 1300-

72-7. Its Molecular mass was 208.21g.mol-1 and Molecular formula was C8H9NaO3S.


3.1.2. Surfactants

The detail information about the surfactants used for the solubilization of drugs is as

under:

a) Tween 20

It was obtained from E. Merck (Germany), its Product No. was 655205-250 mL and CAS

No was 9005-64-5. Its Molar mass was 1309.7g.mol-1, hydrophile-lipophile balance

(HLB) was 16.7, and Molecular formula was C12S6E2.0 (E20 means having 20 oxyethylene

units). Whereas its structure is given below:

X+Y+W+Z= 20

19

b) Tween 80

It was obtained from Merck (Germany), its Product No. was 9490 and CAS No. was

9005-64-5. Its Molar mass was 1228 g.mol-1, HLB was16.7, and Molecular formula was

C18S6E20. Whereas its structural is given below:

W+X+Y+Z= 20

c) Brij 30

It was obtained of Merck (Germany), its Product No. was P4391 and CAS No. was 9002-

92-0. Its Molar mass was 392 g.mol-1, HLB (hydrophile-lipophile balance) was 9.7, and

Molecular formula was (C20H42O5)n. Whereas its structural formula is given as follows:

d) Brij 35

It was obtained from Merck (Germany), its Product No. was 203724-1L and CAS No.

was 9002-92-0. Its Molar mass was 1198 g.mol-1, HLB (hydrophile-lipophile balance)

wass16.9, and Molecular formula was C12H25 (OCH2CH2) 23OH. Whereas its structural

formula is given below:

20

e) Triton X-100

It was purchased from Sigma-Aldrich (UK), its Product No. was X100 and CAS No. was

9002-93-1. Its Molar mass was 625 g.mol-1, HLB (hydrophile-lipophile balance) was

13.5, and Molecular formula was t-Oct-C6H4-(OCH2CH2)n OH. n=9, 10. Whereas its

structural formula is given below:

n=9,10

f) Triton X-114

It was obtained from Sigma-Aldrich (UK), its Product No. was X114 and CAS No. was

9036-19-6. Its Molar mass was 536 g.mol-1, HLB was 12.4, and Molecular formula was t-

Oct-C6H4-(OCH2CH2)n OH. n=7, 8. Whereas its structural formula is given below:

n=7,8

g) N-dodecyl- N, N-dimethyl-3-ammonio-1-propanesulfonate (DDAPS)

It was purchased from Fluka (UK), its Product No. was 40232 and CAS No. was 14933-

08-5. Its Molar mass was 335.55 g.mol-1, and Molecular formula was

C12H25N(CH3)2(CH2)3SO3. Whereas its structural formula is given below:

21

h) N, N-Dimethyl dodecyl amine N-oxide

It was obtained from Sigma (UK), its Product No. was 40103 and CAS No. was 2605-79-

0. Its Molar mass was 201.35 g.mol-1 and Molecular formula was CH3(CH2)9N(O)(CH3)2.


i) Sodium dodecyl sulphate (SDS)

It was purchased from BDH (UK), its Product No. was 44215. Its Molar mass is 288.35

g.mol-1 and Molecular formula was CH3(CH2)11SO4Na. Whereas as its structural formula

is given below:

j) Dodecyl trimethyl ammonium bromide (DTAB)

It was purchased from Sigma (UK), its Product No. was D8638 and CAS No. was 1119-

94-4. Its Molar mass was 308.34 g.mol-1 and Molecular formula was

CH3(CH2)11N(CH3)3Br. Whereas its structural formula is given below:

22

3.1.3. Menthol

It was the purchased from Alfa Aesar (UK), its Product No. was A10474 and CAS No.

was2216-51-5. Its molar mass 156.27 g.mol-1, and Molecular formula was C10H20O.

Whereas its structural formula is given as below:

3.1.4. Drugs

a) Celecoxib

It was purchased from Alfa Aesar (UK), its Product No. was PZ0008 and CAS No was

169590-42-5. Its molar mass was 381.373g.mol-1 and Molecular formula was

C17H14F3N3O2S. Whereas the structural formula is provided below:

b) Meloxicam

It was the purchased from Sigma (UK). Its Product No. was M3935 and CAS No. was

71125-38-7. Its Molar mass was 351.407g.mol-1 and Molecular formula was C14 H13

N3O4 S2. Whereas its structural formula is provided below:

23

c) Lidocaine

It was the purchased from Sigma (UK). Its Product No. was L-7757-25G. Its Molar mass

was 234.34g.mol-1 and Molecular formula was C14H22N2O. Whereas its structural formula

is given below:

d) Ibuprofen

It was the purchased from Fluka (UK), its Product No. was 77519-1G and CAS No.

15687-27-1. Its Molar mass was 206.28g.mol-1 and Molecular formula was C13H18O2.

Whereas its structural formula is provided below:

24

3.1.5. Oils

a) n-Hexane

It was the purchased from Sigma-Aldrich (UK). Its Product No. was 296090 and CAS

No. was 110-54-3. Its Molar mass was 86.18 g.mol-1 and molecular formula was CH3

(CH2)4CH. whereas its structural formula is given below:

b) n-Decane

It was the purchased from Sigma-Aldrich (UK), Its Product No. was 457116 and CAS

No. was 124-18-5. Its Molar mass was 142.28 g.mol-1 and Molecular formula was

CH3(CH2)8CH3. Whereas its structural formula is given as follows:

c) n-Tetradecane

It was the purchased from Sigma-Aldrich (UK), Its Product No. was 172456 and CAS

No. was 629-59-4. Its Molecular mass was 198.39 g.mol-1 and Molecular formula was

CH3 (CH2)12CH3. Whereas its structural formula is given below:

25

3.2. Methods

3.2.1. Sample preparation

Solutions of surfactants, hydrotropes or microemulsions were prepared in triply distilled

and deionized water (solvent) at 25oC. For the preparation of surfactants and hydrotropes

solutions, required amount of surfactants and hydrotropes were added to water and were

stirred for 30 minutes using magnetic stirrer. Further dilution was made by diluting the

freshly prepared stock solutions with water. All the microemulsion samples were

prepared by adding surfactants necessary to solubilize the required amount of oil and then

different amount of water was added slowly along with stirring till the total mass of

mixture became 1gm. These samples were stirred vigorously, till the formation of clear

solution was obtained while the temperature was kept at 25 0C. The area of the

microemulsion existence was determined by preparing microemulsion samples and

transferring to screw caped glass vials and stored at 25 0C for a period of one month in

order to check their thermodynamic stability. The samples which remained completely

clear and non-birefringent (their refractive index remained constant with the passage of

time) solution when observed through crossed Polaroid were classified as

microemulsions.

3.2.2. Phase diagram

Stable microemulsion formulations were plotted on the triangular phase diagram and

identified as cloudy or clear emulsion. The area of microemulsions existence was

determined twice in order to minimize the error and to ensure the accuracy up to 1%w/w

of oil for each sample.

26

3.2.3. pH measurement

The pH of buffer solution and hydrotropes solutions was measured before and after

addition of drugs using pH meter (Denver Instrument Company England). The pH meter

was calibrated using standard buffer solutions of known pH before the measurements

were made.

3.2.4. Estimation of minimum hydrotropic concentration

The minimum hydrotropic concentration, MHC was determined by surface tension

measurement. The surface tensions of the hydrotropes used was determined by

employing tensiometer, Lauda (TEIII), Germany. The calibration of tensiometer was

made by employing the known weight supplied by the manufacturer and then the surface

tension of pure deionized water was determined. The temperature was kept constant at 25

±0.01oC by using water bath, Lauda (E200), Germany. The surface tension data was

divided into two series. The first series was considered up to concentration where the

effect of concentration over the surface tension became negligible and the series two was

considered as rest of the data. Both were subjected to linear regression and the equations

obtained were solved simultaneously to get their crossing point. The concentration at

which these two lines crossed was considered as MHC.

3.2.5. Estimation of critical micelles concentration

The critical micelles concentration, CMC of surfactants was estimated by surface tension

measurement. The surface tensions of the surfactants used was determined by employing

tensiometer, Lauda (TEIII), Germany. The same procedure was adopted for measurement

of critical micelle concentration as that of minimum hydrotrope concentration

27

3.2.6. Centrifugation

The instrument used for the centrifugation was ultra-centrifuge machine supplied by

Sigma UK. The drug loaded samples of surfactants and microemulsions were taken in

ependrof tube of volume 1.5mL and were centrifuged at 1000/15000 rpm for 30 minutes.

The supernatants were collected for further study.

3.2.7. Measurement of solubility

The solubility of the drugs used during the study was determined by employing IRMECO

UV/Vis spectrophotometer (model U2020), USA. For the purpose 1mL of surfactants

solutions /microemulsion and 5mL of hydrotropic solution was saturated separately with

the drug in order to ensure their maximum solubility. The vials containing excess amount

of drugs and surfactants solutions/microemulsions or hydrotropes solutions were sealed

with screw caps and wrapped with para-film in order to avoid the loss of sample through

evaporation. The drug loaded samples of surfactants/microemulsion and hydrotropes

were continuously stirred by employing magnetic stirrer for 72 hrs. at 25±0.5oC, and the

solubility of the drugs was determined after an interval of one hour and plotted vs time. It

was noted that all the drugs attained the equilibrium around 24 hrs. Therefore the data

was obtained after 24 hrs and reported over here. The excess amount was settled down in

the form of amorphous material. Centrifugation of these samples was then made at 15000

revolutions per minute by using ultra centrifuge machine. The aliquot was then diluted up

to the required concentration by using the same surfactant solution/microemulsion of

same concentrations. The UV/Vis measurements were made at the wavelengths equal to

λmax of each investigated drug. The blanks used in this respect were respective surfactant

28

solution/microemulsion or hydrotrope solution having the same concentration as that of

samples. The amount of drugs was calculated by using Beer-Lambert law.

3.2.8. Differential scanning calorimetry

The DSC study of Menthol, Lidocaine and their mixture was performed using Diamond

DSC supplied by Perkin Elmer (UK), installed with Pyris software to analyze the results.

For the purpose, the temperature was varied from 30oC to 100oC at the rate of 5oC/minute

under the atmosphere of nitrogen. The flow rate was kept at 50 mL/mint for the entire

investigation.

3.2.9. Laser light scattering measurement

For the study of size and shape of aggregates formed by the micelles of surfactants or

microemulsions stabilized by suitable surfactants, the static and dynamic light scattering

techniques were employed. Two different instruments were employed for the purpose.

MALS (multi angle light scattering) DAWN EOS (Enhanced Optical system) for static

light scattering and QELS for quasi elastic light scattering, supplied by Wyatt

Technologies Corporation, USA. The ALV/DLS/SLS-5022F compact goniometer system

(ALV, Langen, Germany) and an ALV-5000/EPP multiple-real time correlator (designed

to perform dynamic (DLS) and static light scattering (SLS) measurements

simultaneously) were used in the present study. A JDS Uniphase helium/neon laser

(vertically polarized beam, 22mW laser power at wavelength 632.8 nm, Manteca, CA,

model 1145P-3083) was used as the light source. The temperature of the sample was

determined using a Pt-100 temperature probe (sensitivity ± 0.2K) inserted in the index

matching fluid (filtered toluene) bath in which the sample cell was housed. ALV-

29

5000/E/WIN software (ALV, Langen, Germany) was used for data analysis. Prior to the

measurements, all the samples were filtered through a 0.2 µm polycarbonate filter

(Millipore, Bedford, MA, USA) into dust-free sample cells. The scattering and diffusion

coefficient of each sample was measured at 30o and 150o scattering angles by a difference

of 10 degrees. Filtered toluene was used as a standard in the present study because its

Rayleigh Ratio was accurately known as 1.406 × 10-5 cm-1 at 633 nm. The data was fitted

using the method of cumulant analysis from the standard ALV software which derived

the apparent hydrodynamic radii of the particles assuming them spherical.

3.2.10. Refractive index measurement

Abbs 60/ED refractometer was employed for the measurement of the refractive index of

surfactants, hydrotropes and microemulsion samples. The Abbe 60/ED refractometer

contained sodium lamp as light source for enlightenment of samples. A wavelength

compensation device was employed for chromatizing to mean sodium wavelength

(589.3nm). Refractive index was read directly from the scale divided up to 0.0001.

Temperature control was achieved by circulating the water of required temperature.

30

4. RESULTS AND DISCUSSION

4.1. Estimation of minimum hydrotropic concentration

The surface tension of NaSal, NaBen, NaPTS and NaXS solution was obtained over a

wide range of concentration at 25oC. The results obtained were plotted as a function of

their concentration. The plot showed an expected trend of variation in surface tension

with the concentration, indicating that the surface tension was decreased with the increase

in concentration and became constant after certain concentration (Figure 1). However, the

extent of decrease in surface tension of water with the addition of hydrotropes was

different for a particular concentration of hydrotropes. Further the concentration of

hydrotropes at which the surface tension became constant, known as minimum

hydrotropic concentration (MHC) was also different. NaBen showed the highest ability to

decrease the surface tension than the others. The detail about its exact measurement is

stated in experimental part. The MHC values of hydrotrope ranged from 0.38 to 0.62

mol.L-1 (Table 3). The results were almost the same, as available in the literature [81-82].

The order of the MHC was NaSal > NaBen > NaPTS > NaXS. The trend in decrease in

surface tension and MHC can be due to variation in structure / molecular mass and

dissociation ability of the material.

31

Figure 1 Surface tension as a function of hydrotrope concentration measured at

25oC

40

50

60

70

80

0 0.2 0.4 0.6 0.8 1

Surface tension (mN.m

‐1)

Concentration of hydrotropes (mol.L‐1)

NaSal NaPTS Naxs NaB

32

Table 3 Minimum hydrotropic concentration (MHC) calculated from Figure 1 and

the one available in the literature

Hydrotrope MHC(Exp) (mol.L-1) MHC(Lit) (mol.L-1)

Sodium salicylate 0.62 0.60 [81]

Sodium benzoate 0.48 0.50 [82]

Sodium p-toluene sulfonate 0.40 0.37 [81]

Sodium xylene sulfonate 0.38 0.40 [81]

33

4.2. Solubility of drugs in water

Saturated solution of Meloxicam, Celecoxib Lidocaine and Ibuprofen drugs was made in

pure water. The absorbed light intensity of the solution was measured by UV

spectroscopic measurements at λmax 363, 252 263 and 272 nm for Meloxicam, Celecoxib,

Lidocaine and Ibuprofen, respectively. The solubility was calculated using standard

curves technique of these drugs and displayed in Table 4. The solubility results indicated

that it was comparable to the ones reported in the literature for the same drugs [83-86].

Table 4 Solubility of drugs in water; measured at 25oC

Drugs Solubility (µg/ml)

Meloxicam 7.15

Celecoxib 5.41

Lidocaine 8.41

Ibuprofen 49.00

4.3. Solubility of drugs in buffer solution

In order to explore the effect of pH over the solubility of drugs in water the buffer

solutions of various pH (1-12) were prepared. These buffer solutions were then saturated

with model drugs and the solubility of these drugs was measured and found that it

increases for ibuprofen, meloxicam and decreases for Lidocaine whereas it almost

remains constant for Celecoxib with the increase in pH (Table 5).

34

Table 5 Solubility of drugs at various pH.

Drug Maximum Solubility of drug(mg.mL-1)

Ibuprofen

pH = 1.00 pH =6.00 pH = 7.00 pH = 9.00 pH = 12.00

0.02 0.23 0.85 7.54 31.53

Meloxicam 0.00057 0.0062 0.00715 3.84 18.20

Lidocaine 7.23 0.0483 0.00841 0.00614 0.0024

Celecoxib 0.0027 0.00332 0.00541 0.2588 0.3413

4.4. Effect of hydrotropes over the solubility of drugs

The effect of hydrotropes addition to water and phosphate buffer (pH 7) over the

solubility of drugs was investigated using sodium benzoate, sodium salicylate, sodium

xylene sulfonate and sodium p-toluene sulfonate hydrotropes. The obtained results

indicated that the solubility was increased significantly beyond the Minimum Hydrotrope

Concentration (MHC) of hydrotropes (Figures 2-17) as observed by others for other

systems [87]. These results further indicated that the solubility of the drugs was due to the

formation of aggregates of the hydrotropes rather than change in pH due to addition of

hydrotropes; it most probably means that the drugs got solubilized only in the interior

part of aggregates of hydrotropes [88-90]. It can also be explained in this way as well that

the drugs being hydrophobic and the interior part of aggregates just like micelles in case

of surfactants is hydrophobic hence the drug can easily interact with it and get

solubilized. However, the solubility of the drugs became constant after certain

concentration of hydrotropes, referred as maximum hydrotrope concentration Cmax and it

remained constant, irrespective of the drug solubilized or concentration of hydrotrope

35

(Figures 2-17). This is due to the facts that the aggregates are saturated with drugs and

cannot hold or sustain the drugs any more [91]. This was the reason that the Cmax value

was different for different hydrotropes and varied from 2.00 to 2.25 mol.L-1 for the

hydrotropes investigated (Table 6).

Figure 2 Solubility of Meloxicam in aqueous solution of sodium benzoate as a

function of concentration and temperature

0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5

Solubility of Meloxicam (mg.mL‐1)

Concentration of sodium benzoate (mol.L‐1)

298K 303K 308 K 313 K

36

Figure 3 Solubility of Meloxicam in aqueous solution of sodium salicylate as a


0

2

4

6

8

0 0.5 1 1.5 2 2.5 3 3.5


Concentration of Sodium salicylate (mol.L‐1)

298K 303K 308 K 313 K

37

Figure 4 Solubility of Meloxicam in aqueous solution of sodium p-toluene sulfonate

solution as a function of concentration and temperature

0

1.5

3

4.5

6

0 0.5 1 1.5 2 2.5 3 3.5


Concentration of sodium p‐toluene sulfonate (mol.L‐1)

298K 303K 308 K 313 K

38

Figure 5 Solubility of Meloxicam in aqueous solution of sodium xylene sulfonate as a


0

2

4

6

8

0 0.5 1 1.5 2 2.5 3 3.5

Solubility of Meloxicam (mg.mL ‐1)

Concentration of sodium xylene sulfonate (mol.L‐1)

298K 303K 308 K 313 K

39

Figure 6 Solubility of Celecoxib in aqueous solution of sodium benzoate as a


0

2

4

6

8

0 0.5 1 1.5 2 2.5 3 3.5

Solubility of Celecoxib (mg.mL‐1)

Concentration of sodium benzoate (mol.L‐1 )

298K 303K 308 K 313 K

40

Figure 7 Solubility of Celecoxib in aqueous solution of sodium salicylate as a


0

2

4

6

8

0 0.5 1 1.5 2 2.5 3 3.5

Solubility of Celecoxib (mg.mL

‐1)

Concentration of sodium salicylate (mol.L‐1)

298K 303K 308 K 313 K

41

Figure 8 Solubility of Celecoxib in aqueous solution of sodium p-toluene sulfonate as

a function of concentration and temperature

0

2

4

6

0 0.5 1 1.5 2 2.5 3 3.5

Solubility of Celocoxib (mg.mL

‐1)


298K 303K 308 K 313 K

42

Figure 9 Solubility of Celecoxib in aqueous solution of sodium xylene sulfonate as a


0

2

4

6

0 0.5 1 1.5 2 2.5 3 3.5

Solubility of Celecoxib (mg.mL

‐1)

Concentration of Sodium xylene sulfonate (mol.L‐1)

298K 303K 308 K 313 K

43

Figure 10 Solubility of Lidocaine in aqueous solution of sodium benzoate as a


0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5

Solubility of Lidocaine (mg.mL

‐1)

Concentration of Sodium benzoate (mol.L‐1)

298K 303K 308 K 313 K

44

Figure 11 Solubility of Lidocaine in aqueous solution of sodium salicylate as a


0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5


‐1)


298K 303K 308 K 313 K

45

Figure 12 Solubility of Lidocaine in aqueous solution of sodium p-toluene as a


0

2

4

6

0 0.5 1 1.5 2 2.5 3 3.5


‐1)


298K 303K 308 K 313 K

46

Figure 13 Solubility of Lidocaine in aqueous solution of sodium xylene sulfonate as a


0

2

4

6

8

0 0.5 1 1.5 2 2.5 3 3.5


‐1)


298K 303K 308 K 313 K

47

Figure 14 Solubility of Ibuprofen in aqueous solution of sodium benzoate as a


0

1

2

3

4

5

6

0 0.5 1 1.5 2 2.5 3 3.5

Solubility of Ibuprofen (mg.mL‐1)

Concentration of sodium benzoate (mol.L‐1)

298K 303K 308 K 313 K

48

Figure 15 Solubility of Ibuprofen in aqueous solution of sodium salicylate as a


0

1

2

3

4

5

6

0 0.5 1 1.5 2 2.5 3 3.5



298K 303K 308 K 313 K

49

Figure 16 Solubility of Ibuprofen in aqueous solution of sodium p-toluene sulfonate

as a function of concentration and temperature

0

1

2

3

4

5

0 0.5 1 1.5 2 2.5 3 3.5


Concentration of sodium p‐toluen sulfonate (mol.L‐1)

298K 303K 308K 313K

50

Figure 17 Solubility of Ibuprofen in aqueous solution of sodium xylene sulfonate as

a function of concentration and temperature

0

1

2

3

4

5

6

0 0.5 1 1.5 2 2.5 3 3.5



298K 303K 308K 313K

51

Table 6 Maximum hydrotropic concentration calculated from Figures 2-17

Hydrotropes CMax (mol.L-1)

Sodium salicylate 2.00

Sodium benzoate 2.25

Sodium p-toluene sulfonate 2.00

Sodium xylene sulfonate 2.00

The solubility of all the investigated drugs in hydrotropes was in the order of Sodium

benzoate > sodium salicylate > sodium xylene sulfonate > sodium p-toluene sulfonate.

The solubilization of drugs in water as well as in hydrotropes is certainly a complicated

phenomenon and hence several mechanisms have been proposed, however, the most

plausible explanation for the purpose is the stacking complexation; chaotropy, i.e.,

breakdown of water structure; and /or the formation of micelles/ aggregates by the

hydrotropes in which the drug is solubilized [92-95]. The stacked arrangement reduces

the exposure of the hydrophobic regions to water and hence enhances the solubilization

[94, 96]. The complexation is encouraged by pi-electron of aromatic group of the drugs

overlapping [97], whereas the aggregation process is due to the electrostatic forces or

hydrogen bonding [94, 96, 98]. The same trend has been observed in our investigated

hydrotropes and drug system.

52

From these observations, it can be concluded that the information about the MHC and

Cmax values for the hydrotrope /solute system has significance in detecting the maximum

and minimum solubility limit of the drugs in a particular system. The solubility of the

drugs in the above mentioned hydrotropes was also obtained at various temperatures and

found to increase with the increase in temperature, irrespective of drugs or hydrotropes,

whereas the Cmax remained almost constant [Figures 2-17]. These plots can be exploited

for the estimation of hydrotrope required to solubilize a particular amount of drugs at a

particular temperature; in other words these plots can help in formulating a drug system

accurately. As the solubility of the drug is very much dependent upon the concentration

of hydrotropes and temperature, hence to estimate the drug that can be solubilized for a

particular system can be estimated by their molar solubilization ratio (MSR), an amount

of drug solubilized by one mole of aggregated hydrotrope [99]

(1)

Where St is total amount of drug solubilized at maximum hydrotrope concentration, SMHC

is the amount of drug solubilized at MHC, CMax is the maximum hydrotrope

concentration in solution and MHC is the minimum hydrotropic concentration. As above

MHC, the hydrotropes monomer concentration is equal to MHC so “CMax – MHC” is

considered to be concentration of hydrotrope. MSR can be defined as

(2)

The hydrotropic aggregate-water partition coefficient, KM can be defined as the amount

of drug solubilized in the aggregates of hydrotropes per amount of drug solubilized in

water for a specific amount of hydrotrope. It can be written as:

53

(3)

Where mole fraction of drug in aggregates can be denoted as Xagg and defined as

(4)

And the mole fraction of drug in aqueous phase (Xaq) can be defined as

(5)

The molar volume of water can be denoted as Vm and is equal to 0.01805 dm3.mol-1. By

putting the value of Xagg and Xaq in Equation (3) we obtained the expression for KM as

=

(6)

The process of solubilization can be better understood by having the information about

the thermodynamic characteristics of the drug that are involved in the process.

Thermodynamically, it can be stated that the solubility of drugs is the distribution of drug

among aggregates of hydrotropes and in aqueous phase and more the change in free

energy is better are interactions or more the solubility will be. The free energy of

solubilization (∆Gs0) can be estimated by employing Equation (7)

∆Gs0 = -RT ln KM (7)

Where R is the gas constant, T is the absolute temperature and KM is the molar partition

co-efficient among the aggregates and aqueous phase. The values calculated for MSR,

KM and ∆Gs0 are reported in Tables 7-10. All the systems investigated have negative

54

value of ∆Gs0, which indicated that the process of solubilization is unprompted and

solubility has direct relation with the change in free energy.

Table 7 Various parameters of Meloxicam in aqueous solution of hydrotropes;

measured at 25oC.

Hydrotropes MSR* Log KM ∆Gso (KJ.mol-1)

Sodium benzoate 0.00600 1.98 -11.30

Sodium salicylate 0.00565 1.92 -10.90

Sodium p-toluene sulfonate

0.00220 1.55 -08.84

Sodium xylene sulfonate

0.00370 1.81 -10.32

* MSR, KM, ∆Gs0 stand for molar solubilization ratio, partition coefficient and equilibrium free energy change, respectively

55

Table 8 Various thermodynamic parameters of Celecoxib in aqueous solution of

hydrotropes measured at 25oC.

Hydrotropes MSR Log KM ∆Gso (KJ.mol-1)




0.0014 1.39 -7.93


0.0025 1.62 -9.24

56

Table 9 Various thermodynamic parameters of Lidocaine in aqueous solution of






0.0052 1.75 -9.98


0.0077 1.91 -10.89

57

Table 10 Various thermodynamic parameters of Ibuprofen in aqueous solution of






0.0036 1.57 -8.95


0.0054 1.76 -10.04

58

4.5 Estimation of critical micelles concentration of surfactants

The surface tension of Tween 20, Tween 80, Brij 30, Brij 35, Triton X-100, Triton X-

114, DDAO, DDAPS, SDS and DTAB measured as a function of their concentration at

25oC was plotted in Figures 18-24. The results gave nice curves against the variation in

concentration as expected for surfactants. It can be noted from these curves that the

surface tension was decreased with the increase in amount of surfactants in the solution

and becomes constant after certain concentration and this concentration was called as

critical micelles concentration (CMC) of the surfactant. The CMC calculated from the

data as stated in experimental section is depicted in Tables 11-12 and are almost the same

as reported in the literature [99-104].

59

Figure 18 Surface tension of aqueous solution of Tween 20 as a function of its


35

45

55

65

75

85

0 20 40 60 80 100 120


‐1)

Concentration of Tween 20 (mg.L‐1)

60

Figure 19 Surface tension of aqueous solution of Tween 80 as a function of its


35

45

55

65

75

85

0 5 10 15 20 25 30


‐1)

Concentration of Tween 80 (mg.L‐1)

61

Figure 20 Surface tension of aqueous solution of Triton X-100 as a function of its


32

42

52

62

72

82

0 20 40 60 80 100 120 140 160


‐1)

Concentration of Triton X‐100 (mg.L‐1)

62

Figure 21 Surface tension of aqueous solution of Triton X-114 as a function of its


35

45

55

65

75

85

0 20 40 60 80 100 120 140


‐1)

Concentration of Triton X‐114 (mg.L‐1)

63

Figure 22 Surface tension of aqueous solution of surfactants as a function of their

concentration and measured at 25oC

30

35

40

45

50

55

0 5 10 15 20 25


‐1)

Concentration of surfactnats (mmol.L‐1)

DTAB

DDAO

SDS

64

Figure 23 Surface tension of aqueous solution of Brij 30 as a function of its


35

40

45

50

0 0.02 0.04 0.06


‐1)

Concentration of Brij 30 (mmol.L‐1)

65

Figure 24 Surface tension of aqueous solution of Brij 35 as a function of its


44

48

52

56

60

0.02 0.04 0.06 0.08


‐1)

Concentration of Brij 35 (mmol.L‐1)

66

Table 11 CMC of the surfactants determined from the surface tension of their

aqueous solution and the one available in the literature. The aggregation number is

obtained from the literature.

Surfactants CMC (mg.L-1) Aggregation

number

Experimental Literature

Tween 20 64.2 60 [99] 52 [99]

Tween 80 15.1 13 [99] 133 [99]

Brij 30 10.3 8.3 [100] 101 [100]

Brij35 77.0 74 [100] 40 [100]

Triton X- 100 132.0 130 [100] 146 [100]

Triton X- 114 115.0 110 [100] 189 [100]

67

Table 12 CMC of the surfactants determined from the surface tension of their

aqueous solution and the one available in the literature. The aggregation number is

obtained from the literature.

Surfactants CMC (mmol.L-1) Aggregation

number Experimental Literature

Brij-35 0.051 0.050 [101] 40 [101]

Brij-30 0.034 0.035 [101] 101 [101]

DDAO 1.820 1.800 [103] 76 [103]

SDS 8.200 8.000 [102] 62 [102]

DTAB 14.700 14.600 [102] 74 [102]

DDAPS 2.500 2.500 [104] 67 [104]

68

4.6. Effect of surfactants over the solubility of drugs

The solubility of Meloxicam, Celecoxib, Ibuprofen and Lidocaine was determined by

adding various amounts of surfactants to water. Though the solubility was increased with

the additions of surfactants to the solution but a noticeable increase was observed when

the concentration of surfactants was increased beyond the CMC (Figures 25-29). The

order of solubility in the investigated non-ionic surfactants for Meloxicam and Celecoxib

was Tween 80> Tween 20> Brij 35>Triton X-114> Triton X-100> Brij 30. For

Lidocaine, the order of solubility in the investigated non-ionic surfactants was Dimethyl

dodecyl amine-N-oxide > Brij 35 > Brij 30. As the solubility of Ibuprofen has already

been investigated in a number of ionic and nonionic surfactants [105-106] hence we

determined it’s solubility only in two surfactants, DDAPS and DDAO and the order of

solubility in these surfactants was DDAPS>DDAO. In case of Tween 20 and Tween 80

though the number of oxyethylene units is present in these surfactants is same but their

HLB value for Tween 80 is lower than Tween 20 which may result micelles of larger size

and hence may solubilize more drug [99]. To get a reason behind the enhancement of

solubility of drugs in micelles, we have compared the solubility with aggregation number

of the micelles available in the literature [99-100]. It was concluded that higher the

aggregation number of micelles more the drug is solubilized indicating that the drug is

entrapped in the inner core of the micelles. This can be the reason for Tween 80 showing

high ability for drug solubilization (Table 11). In case of Brij 30, though its aggregation

number was higher than Brij 35 but drug solubilizing capacity of Brij 35 was higher and

was attributed to oxyethylene units which were high in Brij 35.

69

Triton X-114 showed higher solubilizing ability of drugs as compared to Triton X-100. It

was also attributed to low HLB value, greater number of OE units and high aggregation

number. The solubility of drug in DDAO was high due to interactions of amino oxide

group of DDAO with Lidocaine. From these observations, it can be concluded that the

HLB value and oxyethylene units in the surfactant molecules play important role in

solubilization of drugs. The molecular structure of drugs also played a significant role in

solubilizing them in surfactants; if a group in drugs can interact with the surfactant they

will show high solubility and this is the reason that Lidocaine showed high solubility as

compared to Meloxicam Celecoxib and Ibuprofen [93]. The drug solubilization of

Lidocaine in various ionic and zwitterionic surfactants showed DDAPS > DTAB > SDS

order. It can be noted that the stated surfactants have different head groups but the same

hydrophobic chain length and have difference solubilizing ability for Lidocaine. The

plausible reason can be difference in interactions of Lidocaine with head groups of

surfactants used; whereas DTAB has the ability to solubilize lesser amount of drugs than

DDAPS due to having short chain length. All this discussion concluded that there are

various parameters which control the solubility of drugs in surfactants and impact can

vary from system to system.

70

Figure 25 Solubility of Meloxicam in aqueous solution of nonionic surfactants;

measured at 25oC

0

1.5

3

4.5

6

7.5

9

0.001 0.01 0.1 1 10 100

Solubility

of Meloxicam (mmol.L‐1)

Concentration of surfactants (mmol.L‐1)

Tw20

TW80

BR30

BR35

TRX100

TRX114

71

Figure 26 Solubility of Celecoxib in aqueous solution of nonionic surfactants;

measured at 25oC

0

2

4

6

8

0.001 0.01 0.1 1 10 100

Solubility of Celecoxib (mmol.L‐1)


Tw20

TW80

BR30

BR35

TRX100

TRX114

72

Figure 27 Solubility of Lidocaine in aqueous solution of nonionic surfactants;

measured at 25oC

0

3

6

9

12

15

18

0.001 0.01 0.1 1 10

Solubility of Lidocaine (mmol.L‐1)


Brij30 Brij35 DDAO

73

Figure 28 Solubility of Lidocaine in aqueous solution of various surfactants;

measured at 25oC.

0

3

6

9

12

15

0.4 4 40



DTAB SDS DDAPS

74

Figure 29 Solubility of Ibuprofen in aqueous solution of surfactants; measured at

25oC.

0

2

4

6

8

10

12

14

0.1 1 10 100

Solubility of Ibuprofen (mmol.L‐1)


DDAPS

DDAO

75

It is pertinent to express the solubility of drugs in Rm,s (molar solubilization ratio)

defined in terms of total solubility of drug, Stot, the solubility of drug at CMC, Scmc, the

critical micelles concentration, molar concentration of surfactant in solution, Csurf, and

given as Equation (8) [101,107-108]

, (8)

Since the concentration of monomers in the solution will be equal to total concentration

of surfactant minus the concentration of surfactant in micellar form (Csurf-CMC), hence

the above equation can be written as:

,

(9)

The results obtained in this way for Rm,s of the drugs in all the investigated surfactants

are listed in Tables 13-16.

From the solubility data, the partitioned co-efficient, KM was calculated by employing

Equation (10)

KM = (10)

Here XM is the concentration of drug in micelles and Xa is the amount of dug in aqueous

phase. Mathematically, it can be written as:

= ,

, (11)

= (12)

Where, Vm is the molar volume of water and is equal to 0.01805 dm3.mol-1.By

substituting the value of XM and Xa in Equation (10), KM can be obtained as,

76

= ,

, (13)

The results obtained for partitioned co-efficient for drugs in various surfactant systems

are listed in Tables 13-16. It is worth mentioning that the drugs with intermediate polarity

gets solubilized in palisade layer created between the hydrophilic groups and first few

carbon atoms of hydrophobic groups, known as outer core of the micelles [109-110]. The

other expected phase in which these drugs are solubilized is at micellar-water interface

because of hydrogen bonding between C=O, NH, F and OH group of drugs and OE group

of surfactants [111].

The knowledge about thermodynamic properties that control the solubilization process is

quite helpful in understanding the process of solubilization. The addition of drug to the

system containing surfactant results the partitioning of drug among micelles and the

aqueous phase. However, the value of partition coefficient is highly dependent upon the

variation in the free energy of the system. Therefore the standard free energy of

solubilization ∆G∘ can be calculated from the partition coefficient using Equation (14)

[112]

∆G∘ RTlnK (14)

Here∆ ∘, R and T are the standard free energy, gas constant and absolute temperature,

respectively. The values calculated for ∆ ∘ are reported in Tables 13-16 which is

negative for all the explored system, hence the solubilization of drugs is an unprompted

process and that these two parameters are related directly to each other.

77

Table 13 Various parameters of Meloxicam in aqueous solution of surfactants;

measured at 25oC.

Surfactants Rm,s Log KM ∆Gs0 (KJ.mol-1)

Tw 20 0.403 3.92 -22.36

Tw 80 0.470 3.94 -22.47

Brij 30 0.080 3.57 -20.36

Brij 35 0.281 3.82 -21.79

TR X-100 0.210 3.85 -21.96

TR X-114 0.240 3.87 -22.08

78

Table 14 Various parameters of Celecoxib in aqueous solution of surfactants;

measured at 25oC.


Tw 20 0.37 3.87 -22.07

Tw 80 0.42 3.91 -22.30

Brij 30 0.06 3.54 -20.19

Brij 35 0.26 3.78 -21.56

TR X-100 0.18 3.69 -21.05

TR X-114 0.21 3.72 -21.20

79

Table 15 Various parameters of Ibuprofen in aqueous solution of surfactants

measured at 25oC.


DDAPS 0.27 3.71 -21.16

DDAO 0.26 3.52 -20.08

80

Table 16 Various parameters of Lidocaine in aqueous solution of surfactants;

measured at 25oC.


Brij 30 0.026 3.53 -20.0

Brij 35 0.301 3.62 -20.6

DDAO 0.460 3.75 -21.3

SDS 0.211 3.39 -19.3

DTAB 0.220 3.51 -20.0

DDAPS 0.350 3.68 -21.0

81

4.7. Hydrodynamic radius of micelles loaded with drugs

The autocorrelation functions were obtained for the micelles formed by surfactants

dissolved in pure water and the one saturated with drugs using dynamic laser light

scattering technique (Figures 30-36).The hydrodynamic radii obtained in this way are

listed in Table 17 which indicated that the addition of drugs had almost no effect over the

size of micelles for all the investigated surfactants. These observation support the idea

that the drug is solubilized in the inner core of the micelles, hence the aggregation

number and size of the micelles remained constant [113].

Figure 30 Autocorrelation functions obtained by Tween 20 micelles

82

Figure 31 Autocorrelation functions obtained by Tween 80 micelles.

83

Figure 32 Autocorrelation functions obtained by Brij 30 micelles

84

Figure 33 Autocorrelation functions obtained by Brij 35 micelles.

85

Figure 34 Autocorrelation functions obtained by Triton X-100 micelles.

86

Figure 35 Autocorrelation functions obtained by Triton X-114 micelles.

87

Figure 36 Autocorrelation functions obtained by DDAO micelles.

88

Table 17 Hydrodynamic radius of pure and drug saturated micelles of various


Surfactant Hydrodynamic radius of

pure micelles (nm)

Hydrodynamic radius of

drug saturated micelles

(nm)

Tween 20 4.2 4.22

Tween 80 5.3 5.29

Brij 30 3.6 3.6

Brij 35 5.6 5.58

Triton X 100 3.8 3.2

Triton X 114 4.1 3.6

DDAO 3.2 3.25

DDAPS 2.62 2.63

89

4.8. Effect of hydrotropes on critical micelles concentration of DDAPS

The surface tension of DDAPS/water, DDAPS/NaSal/water and DDAPS/NaBen/water

systems was measured at 25oC for various concentration of DDAPS and NaSal or NaBen

and is listed in Tables 18-19. The same data has also been plotted against concentration

of DDAPS in Figures 37-39 which showed a typical trend of surfactants. The figures

indicated that the surface tension was decreased with the increase in concentration of

DDAPS and became constant beyond certain concentration of DDAPS, designated as

CMC of DDAPS. The addition of NaSal to DDAPS solution reduced the surface tension

but the trend remained the same throughout the investigated concentration range (Figure

37), however, the impact was not much visible beyond the CMC of DDAPS. The reason

behind it can be that NaSal gets adsorbed over the micelles and hence had less impact

over the interfacial behavior of the surfactant. A similar trend was observed in case of

NaBen (Figure 38). The CMC was obtained from these data/ plots and found to decrease

with the increase in concentration of hydrotropes added (Figure 39- 40). By the addition

of 0.4 mol.L-1 of sodium salicylate and sodium benzoate, the CMC of DDAPS was

reduced from 2.5×10-3 mol.L-1 (in water) to 1.18×10-3 mol.L-1 and 2.1×10-3 mol.L-1,

respectively. It is to be noted that both of these hydrotropes have aromatic ring and

carboxylate group hence can get adsorbed at the surface of the micelles, resulting a

decrease in surface charge and the CMC [114]. The CMC of DDAPS is reduced more in

the presence of sodium salicylate as compared to sodium benzoate for the same molar

concentration of the hydrotropes. This may be due to the reason that sodium salicylate

contains –OH group that donates its electrons to ring making it electron rich which intern

90

increases its interaction with micellar surface, hence reduces the CMC of DDAPS more

than the later.

Table 18 Surface tension (mN.m-1) of DDAPS in the presence of NaSal measured at

25oC

Concentration

of DDAPS

(mol.L-1)

Amount (mol.L-1) of NaSal added

0.00 0.04 0.08 0.2 0.4

0.0010 49.07 45.6 42.6 40.1 35

0.0012 48.30 41.5 37.6 34.2 31.8

0.0014 47.50 34.6 34.2 31.9 30.4

0.0016 46.15 32.2 32.1 31.0 30.2

0.0018 44.80 30.7 31.3 30.2 30.0

0.0020 42.40 30.5 30.7 30.1 29.3

0.0022 40.60 29.9 29.3 29.7 29.0

0.0025 39.8 29.8 28.9 28.6 28.8

0.0030 39.6 29.6 28.6 28.4 28.4

0.0035 39.6 29.6 28.4 28.2 28.0

91

Figure 37 Variation in surface tension of DDAPS by the addition of sodium

salicylate as a function of DDAPS concentration; measured at 25oC

25

30

35

40

45

50

55

0 0.001 0.002 0.003 0.004 0.005


‐1)

Concentration of DDAPS (mol.L‐1 )

0.04 M NaSal 0.08 M NaSal 0.2 M NaSal

0.4 M NaSal Series1

92

Table 19 Surface tension (mN.m-1) of DDAPS in the presence of sodium benzoate;

measured at 25oC

Concentration

of DDAPS

(mmol.L-1)

Amount (mol.L-1) of sodium benzoate added

0.00 0.04 0.08 0.2 0.4

0.0010 49.07 47.0 45.4 44.2 41.2

0.0012 48.30 43.5 41.4 40.3 38.5

0.0014 47.50 38.9 37.2 35.6 34.3

0.0016 46.15 36.5 34.5 33.1 32.4

0.0018 44.80 33.2 32.3 31.6 30.9

0.0021 42.40 30.2 30.6 29.8 29.5

0.0022 40.60 30.1 29.6 29.2 29.0

0.0025 39.8 29.6 29.3 29.2 28.8

0.0030 39.6 29.5 29.1 29.1 28.6

0.0035 39.6 29.4 29.0 28.9 28.4

93

Figure 38 Variation in surface tension of DDAPS by the addition of sodium

benzoate; measured at 25oC

27

32

37

42

47

52

0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004


‐1)

Concentration of DDAPS(mmol.L‐1)

0.00 NaBen 0.04 M NaBen 0.08 M NaBen

0.2 M NaBen 0.4 M NaBen

94

Figure 39 Effect of sodium salicylate on CMC of DDAPS measured at 25oC

0

0.6

1.2

1.8

2.4

0 0.1 0.2 0.3 0.4 0.5

CMC of DDAPS (m

mol.L‐1)

Hydrotrope concentration (mol.L‐1)

95

Figure 40 Effect of sodium benzoate on CMC of DDAPS measured at 25oC

2.07

2.1

2.13

2.16

2.19

2.22

0 0.1 0.2 0.3 0.4 0.5

CMC of DDAPS (m

mol.L‐1)

Hydrotrope concentration (mol.L‐1)

96

4.9. Effect of hydrotropes on solubility of drugs in DDAPS

Number of studies has been performed in order to increase the solubility of substrates by

the addition of surfactants [92-97]. The solubility enhancement of substrates (drugs) was

investigated by using DDAPS and its mixture with hydrotropes. The solubility of drugs

was estimated in DDAPS and in the presence of sodium salicylate and sodium benzoate

hydrotropes. The results obtained have been plotted in Figures 41-46.These figures

illustrated that the addition of hydrotropes leads to increase in solubility of drugs though

the trend of the plots remained the same. This was true for all the drugs and both the

hydrotropes investigated. This increase in solubility was attributed to reduction in CMC

which may lead to high number of micelles for the same concentration of DDPAPS.

These observations once again lead to believe that the drugs are solubilized in the inner

core/ internal part of micelles/ aggregates. From these results, the molar solubilization

ratio (Rm,s), micellar partition co-efficient, KM and free energy of solubilization ∆G0 was

calculated using Equations (8-14). The results obtained are summarized in Tables 20-22.

The results indicated that media has a high effect over these parameters rather than the

drugs.

97

Figure 41 Solubility of Lidocaine in aqueous solution of DDAPS/ (0.4mol.L-1) NaSal

mixture; measured at 25oC

0

2

4

6

8

10

1 10


Concentration of DDAPS (mmol.L‐1)

98

Figure 42 Solubility of Meloxicam in aqueous solution of DDAPS/ (0.4mol.L-1) NaSal


0

2

4

6

8

1 10

Solubility of Meloxicam (mmol.L‐1)


99

Figure 43 Solubility of Celecoxib in aqueous solution of DDAPS/ (0.4mol.L-1) NaSal

mixture at 25oC

0

2

4

6

8

1 10



100

Figure 44 Solubility of Lidocaine in aqueous solution of DDAPS/ (0.4mol.L-1) NaBen


0

1

2

3

4

5

6

7

8

1 10



101

Figure 45 Solubility of Meloxicam in aqueous solution of DDAPS/(0.4mol.L-1)

NaBen mixture; measured at 25oC

0

1

2

3

4

5

6

7

1 10

Solubility of Meloxicam (mmol.L‐1)


102

Figure 46 Solubility of Celecoxib in aqueous solution of DDAPS/(0.4mol.L-1) NaBen


0

2

4

6

8

1 10


Concentration of surfactant (mmol.L‐1)

103

Table 20 Various parameters of drugs calculated in the presence of DDAPS at 25oC

Drugs MSR Log KM ∆Gso (KJ.mol-1)

Lidocaine 0.37 3.69 -21.0

Meloxicam 0.33 3.68 -20.9

Celecoxib 0.24 3.62 -20.6

Ibuprofen 0.27 3.71 -21.16

104

Table 21 Various parameters of drugs calculated in the presence of DDAPS/NaSal

at 25oC


Lidocaine 0.54 3.80 -21.68

Meloxicam 0.50 3.78 -21.56

Celecoxib 0.44 3.76 -21.45

Ibuprofen 0.35 3.62 -20.65

105

Table 22 Various parameters of drugs calculated in the presence of DDAPS/NaBen

at 25oC


Lidocaine 0.43 3.73 -21.28

Meloxicam 0.41 3.73 -21.28

Celecoxib 0.38 3.71 -21.16

Ibuprofen 0.31 3.58 -20.42

106

4.10. Aggregation number of DDAPS/NaSal and DDAPS/NaBen

We have also measured the aggregation number of DDAPS/NaSal and DDAPS/NaBen

mixture by employing static laser light scattering technique. For the purpose following

equations were used [115].

‐

∆ 2B C‐C (15)

Here, C and Ccmc are the total concentration (in mol.L-1) of surfactant. Rθ is the excess

Rayleigh ratio, B is second varial coefficient. K is an optical constant calculated as

K /

(16)

Where n is the refractive index of the solvent; dn/dc is the refractive index increment of

the sample; NA is the Avogadro’s number and λ is the wave length of incident light.

The mass of aggregates (in this case Magg) and aggregation number can be calculated as

M (17)

and

N

(18)

The aggregation number of the system DDAPS/NaSal and DDAPS /NaBen obtained in

this way is reported in Tables 23-24. The results indicated that the addition of

hydrotropes to 1.0 to 10 mmol.L-1 concentration of DDAPS increased the aggregation

107

number of DDAPS. This was the reason that this system was able to solubilise higher

amount of drugs as compared to DDAPS alone.

Table 23 Aggregation number of DDAPS micelles formed in aqueous solution of 0.4

molar NaSal; measured at 25oC

Concentration of DDAPS (mol.L-1) Nagg

1.80 116

2.10 132

5.00 158

10.0 167

108

Table 24 Aggregation number of DDAPS micelles formed in aqueous solution of 0.4

molar NaBen; measured at 25oC


1.80 102

2.10 118

5.00 139

10.0 155

109

4.11. Hydrodynamic radius of DDAPS/NaSal and DDAPS/NaBen mixture

The size of DDAPS/NaSal/butanol and DDAPS/NaBen/butanol mixture blank and drugs

loaded in terms of hydrodynamic radius was measured using dynamic light scattering

intensity (Tables 25-26). It was noted that the hydrodynamic radius of DDAPS/NaSal and

DDAPS/NaBen mixture was larger than DDAPS alone. The drug loaded and blank

systems had almost the same hydrodynamic radius. These observations concluded that

the drugs are solubilized in the inner core of aggregates and this is the reason for showing

high solubility in such systems.

Table 25 Effect of addition of NaSal (0.4 mol.L-1) on hydrodynamic radius of


Concentration of butanol

(mol.L-1)

RH blank (nm) RH drug loaded micelles

(nm)

1.80 2.83 2.85

2.10 2.97 3.00

5.00 3.29 3.28

10.0 3.91 3.90

110

Table 26 Effect of addition of NaBen (0.4 mol.L-1) on hydrodynamic radius of

DDAPS measured in water/butanol mixture at 25oC


(mol.L-1)

RH blank (nm) RH drug loaded micelles

(nm)

1.80 2.79 2.80

2.10 2.91 2.93

5.00 3.20 3.22

10.0 3.82 3.84

111

4.12. Effect of addition of butanol on solubility of drugs

Alcohols are polar compounds and interact with micelles formed by the surfactants

through their polar groups [98]. Therefore, it is expected that the addition of alcohol to

the system may alter the solubility of the drug dissolved in surfactant/water system. For

the quantitative estimation of this phenomenon, the solubility of the drugs was measured

in DDAPS/butanol mixture as a function of contents of alcohol. The result showed that

the solubility of drugs was increased by the addition of butanol from 0.2 to 1.2 mol.L-1 in

0.5 mol.L-1 of DDAPS (Table 27).

Table 27 Effect of addition of butanol to water on solubility of drugs in 0.5 mol.L-1 of

DDAPS at 25oC

Contents of

butanol

(mol.L-1)

Ibuprofen

(mmol.L-1)

Meloxicam

(mmol.L-1)

Celecoxib

(mmol.L-1)

Lidocaine

(mmol.L-1)

0.2 33.4 37.40 28.20 39.50

0.5 35.90 38.33 33.25 40.25

0.8 44.60 45.30 38.33 46.30

1.2 52.35 53.60 40.60 54.62

112

4.13. Solubility of drugs in oil-in-water microemulsion

Hexane, Decane or Tetradecane (2% v/v) was dispersed in 0.5 mol.L-1 DDAPS/1.2

mol.L-1 aqueous solution of DDAPS and butanol to get oil-in-water microemulsions.

Theses microemulsions were tested for their ability to solubilize drugs. It was noted that

these microemulsions had greater ability to solubilize drugs than DDAPS/butanol mixture

(Table 28). However, this ability varied with the variation in nature of oil and every oil

showed different ability. The reason behind such trend might be that the drugs and oils

are hydrophobic and hence the drug is dissolved in oil which is then dispersed in the

mixture in the form of microemulsion [116].

Table 28 Effect of addition of 2% (v/v) hydrocarbons over the apparent solubility of

drugs in DDAPS/butanol (0.5 mol.L-1/1.2 mol.L-1) mixture at 25oC

Hydrocarbon

oil

Ibuprofen

(mmol.L-1)

Meloxicam

(mmol.L-1)

Celecoxib

(mmol.L-1)

Lidocaine

(mmol.L-1)

Hexane 60.10 62.54 41.25 63.54

Decane 70.30 73.56 44.12 75.01

Tetradecane 73.70 76.23 47.54 77.58

113

4.14. Aggregation number of DDAPS, DDAPS/butanol and microemulsion

By employing Equations (14-17), the aggregation number of blank and drug loaded

DDAPS micelles were calculated which remained constant (Tables 29-31) even with the

increase in concentration from 0.06 to 0.5 mol.L-1 of DDAPS and with the addition of

drugs. The addition of butanol to DDAPS solution increased the solubility of drugs. In

order to explore and identify the causes of increase in solubility by the addition of

butanol, the aggregation number of the system was measured using light scattering

technique. The calculated aggregation numbers of systems under observations are listed

in Tables 29-31. The addition of butanol to fixed concentration (0.5mol.L-1) of DDAPS

brought an increase in the aggregation number. Therefore, the increase in solubility with

the addition of butanol was the increase in aggregation number. Whereas the addition of

2% v/v Hexane, Decane, or Tetradecane to 0.5 mol.L-1 DDAPS / 1.2 mol.L-1 Butanol

mixture resulted a decrease in aggregation number. It was noted that larger the alkyl

chain length of hydrocarbon oils greater the decrease in aggregation number of

micelles/droplet (Table 29-31). However, the solubility continued to increase by the

increase of alkyl chain length of hydrocarbons.

114

Table 29 Aggregation numbers of DDAPS Micelles in water; measured at 25oC


0.06 63

0.12 63

0.18 63

0.24 63

0.30 63

0.50 63

115

Table 30 Effect of addition of butanol on aggregation number of 0.5 mol.L-1DDAPS;

measured at 25oC

Concentration of butanol (mol.L-1) Nagg

0.2 74

0.5 90

0.8 298

1.2 387

116

Table 31 Effect of addition of 2% (v/v) hydrocarbons over the aggregation number

of DDAPS/butanol (0.5mol.L-1/1.2mol.L-1) mixture; measured at 25oC

Hydrocarbon Nagg

Hexane 373

Decane 364

Tetradecane 359

117

4.15. Hydrodynamic radius of DDAPS/butanol mixture and microemulsions

The results obtained for hydrodynamic radius of blank and drugs loaded DDAPS,

DDAPS/butanol mixture are listed in Tables 32-34. It had been observed that the

hydrodynamic radius of pure micelles was smaller than DDAPS/Butanol mixture due to

the reason stated earlier. The hydrodynamic radius of microemulsions was smaller than

that of DDAPS/butanol mixture. It was noted that the hydrodynamic radii of micro-

emulsions show a decreasing trend with the increase in chain length of the oil used.

Further the drug loaded and blank systems have nearly the same hydrodynamic radius

(Tables 32-34). These results conclude that the stated mechanism of solubilization is

correct and according to expectations.

Table 32 Hydrodynamic radius of blank and drugs saturated DDAPS Micelles

measured at 25oC

Concentration of DDAPS (mol.L-1)

RH blank (nm) RH drug saturated

micelles (nm)

0.06 2.62 2.63

0.12 2.63 2.64

0.18 2.63 2.63

0.24 2.63 2.63

0.30 2.63 2.63

0.50 2.64 2.64

118

Table 33 Effect of addition of butanol on hydrodynamic radius of drug saturated

(0.5mol.-l) DDAPS at 25 oC


(mol.L-1)

RH of blank (nm) RH of drug saturated

micelles (nm)

0.2 2.94 2.93

0.5 3.05 3.07

0.8 3.45 3.47

1.2 4.12 4.14

119

Table 34 Effect of addition of 2% (v/v) hydrocarbons over the hydrodynamic radius

of DDAPS/butanol (0.5mol.L-1/1.2mol.L-1)/drug systems at 25oC

Hydrocarbon RH of blank (nm) RH of drug saturated

micelles (nm)

Hexane 4.10 4.10

Decane 4.08 4.08

Tetradecane 4.06 4.06

120

4.16. Microemulsion having Menthol and/or Eutectic mixture as an oil

For the estimation of eutectic point of Lidocaine /Menthol mixture the system was

subjected to differential scanning calorimetric (DSC). The melting point of Lidocaine and

Menthol as well as their mixture was determined. The mixture which gave single melting

point was considered as eutectic mixture (Figure 47). The ratio of the eutectic mixture

estimated in this way was 30:70 Lidocaine: Menthol and was fluid at room temperature.

Figure 47 DSC curve of Lidocaine/Menthol mixture

121

For the formation of microemulsions (ME1–ME6) water was added to mixture of

surfactant/oil mixture. It was observed that the addition of water to surfactant/oil mixture

resulted in a continuous transition from cloudy to a transparent phase having low

viscosity systems. Three-component triangular phase diagrams of O/W microemulsions

obtained in this way are displayed in Figures 48-50. The results indicated that 40% w/w

DDAPS formed oil-in-water microemulsions with, 9% w/w Menthol and 13% w/w

eutectic mixture of Menthol/Lidocaine. On the other hand 40% w/w DTAB, formed O/W

microemulsion with 10% w/w Menthol and 11% w/w eutectic mixture. Whereas, 20%

w/w SDS gave O/W microemulsion with 10% w/w Menthol and 34% w/w eutectic

mixture (Table 35). These microemulsions were checked for their stability by adding

water to the system. The microemulsions having lowest surfactant concentration were

selected for further investigation (Table 36).

122

SAA0 10 20 30 40 50 60 70 80 90 100

Menthol

0

10

20

30

40

50

60

70

80

90

100

Water

0

10

20

30

40

50

60

70

80

90

100

SAA0 10 20 30 40 50 60 70 80 90 100

Eutectic

0

10

20

30

40

50

60

70

80

90

100

Water

0

10

20

30

40

50

60

70

80

90

100

Figure 48 Phase diagrams of microemulsion stabilized by DDAPS at 25oC

123

SAA0 10 20 30 40 50 60 70 80 90 100

Menthol

0

10

20

30

40

50

60

70

80

90

100

Water

0

10

20

30

40

50

60

70

80

90

100

SAA0 10 20 30 40 50 60 70 80 90 100

Eutectic

0

10

20

30

40

50

60

70

80

90

100

Water

0

10

20

30

40

50

60

70

80

90

100

Figure 49 Phase diagrams of microemulsion stabilized by DTAB at 25oC

124

SAA0 10 20 30 40 50 60 70 80 90 100

Menthol

0

10

20

30

40

50

60

70

80

90

100

Water

0

10

20

30

40

50

60

70

80

90

100

SAA0 10 20 30 40 50 60 70 80 90 100

Eutectic

0

10

20

30

40

50

60

70

80

90

100

Water

0

10

20

30

40

50

60

70

80

90

100

Figure 50 Phase diagrams of microemulsion stabilized by SDS at 25oC

125

Table 35 Composition of microemulsions having the capacity of sustaining

maximum oil

ME 1 ME 2 ME 3 ME 4 ME 5 ME 6

DDAPS 40 40 ---- ---- ----

DTAB ---- ---- 40 40 ----

SDS ---- ---- ---- ---- 20 20

Menthol 9 ---- 10 ---- 10 ----

Eutectic ---- 13 ----- 11 ---- 34

Water 51 47 52 52 70 66

126

Table 36 Composition of oil in water microemulsions obtained from phase diagrams

and can be diluted to a very low surfactant concentration

ME 1 ME 2 ME 3 ME 4 ME 5 ME 6

Composition % w/w % w/w % w/w % w/w % w/w % w/w

DDAPS 40 40 ---- ---- ---- -----

DTAB ---- ---- 40 40 ---- -----

SDS ---- ---- ---- ---- 20 20

Menthol 4 ---- 8 ---- 7 ----

Eutectic ---- 4 ----- 8 ---- 14

Water 56 56 52 52 73 66

127

4.17. Aggregation number of microemulsion having Menthol and Eutectic mixture

as oil

Table 37 represents the aggregation number, calculated using Equations (14-17) of oil-in

water microemulsion having Menthol and/or eutectic mixture as oil. The table indicated

that on addition of menthol and eutectic mixture to DDAPS/Water, DTAB/Water and

SDS/Water mixture increased the aggregation number of the system from 63,65 to 76,87

and 97 for Menthol and 73,98, and 105 for Eutectic mixture when added to above

mentioned systems separately.

Table 37 Aggregation number of microemulsions measured at 25oC

Microemulsions Aggregation number

DDAPS/Menthol 76

DDAPS/Eutectic 73

DTAB/Menthol 87

DTAB/Eutectic 98

SDS/Menthol 97

SDS/Eutectic 105

128

4.18. Hydrodynamic radius of microemulsion having Menthol and Eutectic mixture

as oil

At infinite dilutions, the hydrodynamic radius of micelles (assuming spherical

aggregates) was found to be 2.54, 1.75, and 1.88 nm for DDAPS, SDS and DTAB

micelles, respectively. The hydrodynamic radius of ionic surfactants was very difficult to

obtain by employing laser light scattering technique due to their head groups repulsion

and the ionic surfactants micelles showed a continuous decrease in their size [117]. In

order to get size/hydrodynamic radius of micelles of ionic surfactants and their

microemulsions 0.002M phosphate buffer of pH 7.4 was used as a solvent instead of

water. The size obtained in this way was 2.87/2.94, 3.14/3.21 and 3.02/3.07 nm for

DDAPS, SDS and DTAB microemulsions with Menthol/ Eutectic, respectively (Table

38). It can be noted that the increase in droplet size/micelle enhanced the solubility of

drugs which certainly support our earlier conclusion.

129

Table 38 Hydrodynamic radius of microemulsion measured at 25oC

Microemulsion system Hydrodynamic radius (nm)

DDAPS/Menthol 2.87

DDAPS/Eutectic 2.94

DTAB/Menthol 3.02

DTAB/Eutectic 3.07

SDS/Menthol 3.14

SDS/Eutectic 3.21

130

4.19. Refractive index of various systems

The results obtained for refractive index of DDAPS and its microemulsions with Menthol

and eutectic mixture in water are listed in Tables 39-41 and plotted in Figures 51-53 as a

function of surfactant concentration. The figures showed that the refractive index was

increased linearly with the concentration of surfactant / microemulsions of menthol or

eutectic mixture, showing that the system was quite homogeneous in the investigated

range. The micellar/ microemulsions systems had different refractive index which

indicated that on addition of Menthol or Eutectic mixture to surfactant changed the dipole

moment of surfactant and hence increased the refractive index. Similar trend was also

noticed for DTAB and SDS systems.

Table 39 Refractive index of DDAPS micelles and its microemulsion measured at

25oC

Surfactant

concentration %

(w/w)

Micelle Menthol Eutectic (30:70)

0.2 1.33114 1.33126 1.33148

0.4 1.33128 1.33151 1.33198

0.6 1.33141 1.33175 1.3325

0.8 1.33156 1.33199 1.33291

1 1.33168 1.33225 1.33339

131

Table 40 Refractive index of DTAB micelles and its microemulsion measured at

25oC

Surfactant

concentration

%(w/w)

Micelle Menthol Eutectic 30:70

0.2 1.33135 1.33148 1.33172

0.4 1.33173 1.33198 1.33246

0.6 1.33209 1.33246 1.33321

0.8 1.33245 1.33296 1.33392

1 1.33283 1.33343 1.33465

132

Table 41 Refractive index of SDS micelles and its microemulsion measured at 25oC

Surfactant

concentration %

(w/w)


0.2 1.33123 1.33141 1.33168

;0.4 1.33149 1.33185 1.33239

0.6 1.33174 1.33225 1.33307

0.8 1.33197 1.33266 1.33375

1 1.33222 1.33308 1.33442

133

Figure 51 Refractive index of DDAPS micelles and its microemulsion; measured at

25oC

1.33

1.331

1.332

1.333

1.334

0 0.2 0.4 0.6 0.8 1 1.2

Refractive index

Surfactant concentration % (w/w)


134

Figure 52 Refractive index of DTAB micelles and its microemulsion; measured at

25oC

1.33

1.331

1.332

1.333

1.334

1.335

0 0.2 0.4 0.6 0.8 1 1.2

Refractive

index

Surfactant concentration % (w/w)


135

Figure 53 Refractive index of SDS micelles and its microemulsion; measured at 25oC

1.33

1.331

1.332

1.333

1.334

1.335

0 0.2 0.4 0.6 0.8 1 1.2

Refractive index

Surfactant concentration % (w/w )


136

CONCLUSION

Solubility in an aqueous media is the prerequisite of the drugs; therefore the efforts were

made to enhancement the solubility of Meloxicam, Celecoxib, Ibuprofen and Lidocaine

drug by trying the nature of the aqueous media. For the purpose a solution of

hydrotropes, surfactants, surfactant/hydrotrope, surfactants/butanol mixtures and oil/

water microemulsions were tested and tensiometry, UV/Vis spectrophotometry and light

scattering techniques were employed to understand the mechanism of solubilization and

the various parameters over it. The results obtained in this way concluded that the order

of solubilization of system investigated was hydrotropes < surfactants <

surfactant/hydrotropes mixture < surfactant/Butanol mixture < oil in water

microemulsion. On the other hand Lidocaine drugs had the highest solubility in these

systems whereas Ibuprofen had the lowest. The results also conclude that NaBen

hydrotrope was having high capacity to solubilize the drugs whereas NaPTS has the

lowest. Overall the solubilizing capacity was noted to in the order of NaBen > NaSal >

NaXS >. NaPTS.

The results obtained in case of role of surfactants concluded that surfactant play

significant role in enhancing the solubility of drugs and the effect can be multiplied by

the addition of hydrotropes etc. However, in case of nonionic surfactants oxyethylene

units (OE), HLB and Aggregation number had noticeable impact over their solubilizing

capacity. The addition of hydrotropes and Butanol to aqueous solution of DDAPS not

only affected the solubility of model drugs in DDAPS micelles but also decreased its

CMC. The results also revealed that the addition of hydrocarbons to DDAP/Butanol

mixture (microemulsions) increased the solubility of tested (Ibuprofen) drug and an

137

increase in alkyl chain length of oil further increased the solubility. On the other hand

hydrodynamic radius of micelles remained the same in spite of addition of drugs;

whereas the addition of hydrotropes, Butanol and hydrocarbons to aqueous solutions of

DDAPS lead to an increase in aggregation number. The Hydrodynamic radius and

aggregation number of microemulsions was increased by the addition of Menthol and/or

Eutectic mixture of Menthol/Lidocain. It has therefore been concluded that the drugs with

even very low solubility can be solubilized up to required level by using various

surfactants/ surfactants-hydrotropes systems. However, the problem is very serious in the

sense that the system to be selected must not be dangerous for health and this is really a

big challenge for the scientists.

138

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by IRFAN ULLAH Department of Chemistry, Gomal University