Jurnal Steril Subarna

ISSN 0975-6299 Vol 3/Issue 1/Jan – Mar 2012

International Journal of Pharmaand Bio Sciences

RESEARCH ARTICLEPHARMACEUTICS

FORMULATION DEVELOPMENT AND EVALUATION OF INJECTIONOF POORLY SOLUBLE DRUG USING MIXED SOLVENCY CONCEPT

R. K. MAHESHWARI* AND RAJENDRA SHILPKAR

Industrial Pharmacy Research Lab, Department of Pharmacy,

Shri G. S. Institute of Technology and Science, 23, Park Road, Indore(M.P.) - 452003

R. K. MAHESHWARI

Industrial Pharmacy Research Lab, Department of Pharmacy,

Shri G. S. Institute of Technologyand Science, 23, Park Road, Indore (M.P.) - 452003

ABST

RACT

Mixed solvency, a newconcept of solubilization statesthat all substances whether solids,liquids or gases possesssolubilizing power and henceconcentrated solution containingvarious dissolved substances inany liquid can also improve thesolubility of poorly soluble drugs.Mixed solvency technique can beemployed in injection formulationof poorly soluble drugs in order toreduce concentration of individualsolubilizer (used for solubilityenhancement) to minimize thetoxic effects of solubilizers. Forexample in most of the methods ofaqueous solubilization, highconcentration of an additive(hydrotropicagent/cosolvents/surfactants/cyclodextrins etc.) is required toproduce an appreciable increasein solubility of a poorly watersoluble drug. In this case, thesolubilizing agent employed togive a desirable solubility for thepoorly soluble drug may produceits own toxicity. Similarly, thepresence of several oil solubleadditives (each in smallconcentration) in oil, forming aconcentrated solution mayenhance the oil solubility of apoorly oil soluble drug efficiently.In the present investigation,rifampicin was selected as modelpoorly oil soluble drug. Castor oilwas used as model oil and thymol,menthol, camphor, phenol,ethanol, benzyl alcohol and oleicacid were used as model oilsoluble/miscible addatives. Oilyinjection was made as a result ofoily solubility effect of theseadditives. The results of solubilitystudy revealed the significance ofmixed solvency and the stabilitystudies data supports that thedeveloped formulation using thistechnique gives good stabilityalso.

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KEYWORDSMixed solvency, poorly oil soluble, injection formulation and toxicity issues.

INTRODUCTION

Maheshwari1-5

proposed the concept ofmixed solvency. He is of theopinion that all substanceswhether liquids, gases orsolids possess solubilizingpower and henceconcentrated aqueoussolutions containing variousdissolved substances canalso improve the solubility ofpoorly water soluble drugs.Melted (temperature about60 ºC), PEG 400, PEG 6000and PEG 8000 dissolvesdiclofenac sodium (meltingpoint: 283 ºC). This alsoshows that melted PEGs actas solvent for diclofenacsodium. Melted urea (M.P.:132-135 ºC) dissolvesdiclofenac sodium (M.P.:283ºC). This also shows thatmelted urea act as solvent fordiclofenac sodium. Meltedibuprofen (M.P.:78ºC)dissolves diclofenac sodium(M.P.:283ºC), salicylic acid(M.P.:159ºC) andniacinamide (M.P.:132ºC),which again shows thatmelted ibuprofen act assolvent for diclofenacsodium, salicylic acid andniacinamide respectively. Insupercritical fluid technologyliquefied carbon dioxide actsas solvent for many insolublesubstances. These indicatethat all substances possesssome solvent character.

Mixed solvency is thephenomenon basically toincrease the solubility of poorlysoluble drugs, using blends ofsolubilizers. This techniquecan provide additive orsynergistic enhancementeffect on solubility of poorly

soluble drugs. Utilization ofthis method in theformulation of dosageforms made of insolubledrugs can also reduce theconcentration of individualsolubilizing agents, in orderto minimize the side effects(in place of using a largeconcentration of onesolubilizer, a blend ofseveral solubilizerss can beemployed in much smalleracceptable concentrations,reducing their individualtoxicities). All weakersolvents can be madestrong solvent by properchoice of solubilizer(s).

Hydrotropy is anothertype ofcosolvency6.Hydrotropicagents arealso a type ofsolubilizerswhichincrease thesolubility ofpoorly watersoluble drugs.Mixedhydrotropy isalso a type ofmixedsolvency.Hydrotropy7-11

and mixedhydrotropy12-

14 have alsobeen used toenhance theaqueoussolubility of alarge numberof poorlysoluble drugs.

Theobjective ofpresentresearch is toexplore theapplication ofmixedsolvencytechnique inthe injectionformulation ofpoorly oilsoluble drugand to reduceconcentrationof individualsolubilizer(used forsolubilityenhancement)to minimizethe toxiceffects ofsolubilizers. In

the presentwork,rifampicin, apoorly oilsoluble drugwas selectedas a modeldrug andattempts weremade toformulate anoily injection ofthis drug usingvarious modelsolubilisingagents. Theformulationwas alsostudies forphysical andchemicalstability.

MATERIALS AND METHODS

The giftsample ofrifampicin wasprovided byTorrentPharmaceutical Limited,Ahmedabad,India. Thymol,camphor,menthol werepurchasedfrom localmarket. Ethyloleate oleicacid andphenol (Merck,Ltd., Mumbai,India) werealso used. Allotherchemicals andsolvents usedwere of

analytical grade.

(1) Solubility studies: Solubility studies ofrifampicin were performed

in castor oil, 20% w/vsolution containingindividual solubilizersand in mixed blends ofsolubilizers (20% w/v).

Variousmixedblendswereprepared

forsolubilisation ofrifampicin(Table 1).

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Table 1

Mixed blends prepared for solubilisation of rifampicin

Solubilizers Concentration of solubilizers in blend (%)OB-1 OB-2 OB-3 OB-4 OB-5 OB-6 OB-7

Thymol - - 7 5 6 - 4Menthol - - - - 4 5 4Camphor - - - - - 5 -Phenol 10 5 5 5 - 5 4Ethanol - 5 - - - - 4Benzyl - 5 - 5 6 5 4alcoholOleic acid 10 5 8 5 4 - -

The solubility of rifampicin invarious mixed blends wasdetermined by shake flaskmethod. About 5 ml of eachblend was taken in a vialseparately. To each vial, anexcess amount of rifampicinwas added. Vials wereproperly sealed and stirredusing vortex mixer for 10min for proper mixing. Theywere then kept in orbitalflask shaker (RemiInstruments Pvt. Ltd., India)maintained at 25ºC for 12 hr.The solution was thenallowed to equilibrate for 24hr (undisturbed). After 24 hr,the solutions containingexcess undissolved drugwere transferred intocentrifuge tubes andcentrifuged at 2000 rpm for10 min using a centrifuge(Remi Instruments Pvt. Ltd.,India). The supernatant wassuitably diluted with ethanoland analyzed usingUV/Visiblespectrophotometer(Shimadzu 1700) at 475 nmagainst respective reagentblanks.Solubility enhancement ratiowas determined by usingthe following formula:Enhancement ratio=solubility in mixedblend/solubility in castor oil

(ii) Formulation of injection dosage form:

Initially, the appropriateweighed amounts ofsolubilizers were transferredto 50 ml volumetric flaskcontaining 40 ml of castoroil. The flask was shaken todissolve the solubilizers.After complete dissolution ofsolubilizers, the volume wasmade up to the mark withcastor oil. To prepare oilysolution of drug, thecalculated quantity ofrifampicin was transferred toanother volumetric flask of50 ml and prepared blendsolution was added to it todissolve the drug andshaken for 12 hours at 370C on orbital flask shaker(Remi Instruments Pvt. Ltd.,India) to assure completedissolution of drug. Otherexcipients like chelatingagent, buffering agent,antioxidants were not addedas they may upset the basicsolubility enhancementratio. Finally the volumewas made upto the markwith same blend. Flask wasshaken to get homogenousoily solution of drug.The sterile vials were preand post flushed withnitrogen gas, filled with 2.5ml volume of product,stoppered and sealed withsterile aluminium caps.Formulation compositionsare shown in table 2.

Table 2Co

mpositio

ns of prepared formulations

SolubilizersRifampicin 37.5 mg

Thymol -

Menthol Thi

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Vol 3/Issue 1/Jan – Mar 2012

Phenol 0.125 gm 0.125 gm 0.10 gmEthanol 0.125 ml - 0.10 ml

Benzyl alcohol 0.125 ml - 0.10 mlOleic acid 0.125 ml 0.20 ml -

Castor oil q. s. to 2.5 ml q. s. to 2.5 ml q. s. to 2.5 ml

(iii)Accelerated stability studies:As soon as the product is developed, itwas subjected to ageing as a result, itsphysical properties, chemicalcomposition and even its biologicalavailability may be changed. Theprepared formulations were subjected to2-8 0C, 25 0C, 40 0C and 55 0C toobserve the stability of medicament indeveloped formulations. Samples werewithdrawn after 7, 14, 21 and 28 daysand analysed spectrophotometrically at475 nm after suitable dilution withethanol to determine content ofundecomposed drug. The initialcomposition in the formulation wastaken as 100%.

(iv)Effect of sunlight on drug degradation:

One set of colourless vials containingthe formulations were exposed tosunlight to estimate the effect of light onthe stability of formulations. Other set ofcolourless vials containing formulationwere wrapped with aluminium foil

(controlled) andstored in dark.Both sets ofvials werestored at roomtemperature.One vial ofeachformulation andeach set waswithdrawnevery 7 day upto 28 days,suitably dilutedwith ethanoland observes at475 nm underUV visiblespectrophotometer (Shimadzu1700) todetermine thedrug remained.The initial drugcontent offormulationswas taken as100 % for thestudy.

(5) Effect of

atmosphericoxygen onstability:

To assess theeffect of oxygen,the injection (2ml) was filled in5 ml and 20 mlvials. The air in20 ml capacityampoules wasnot displacedbefore sealing(condition ‘A’),whereas the airpresent in the 5ml capacity vialswas replaced byflushing withnitrogen andsealed(Condition ‘B’).Samples fromboth sets of vialswere withdrawnperiodically at 7day intervals andthe drug contentwas estimated.

RESULTS AND DISCUSSION

(i) Solubility studiesTable 3

Solubility data of rifampicinin solutions containingindividual solubilizers

Solubilizer 20% incastor oil

Castor oil

Thymol (w/v)

Menthol (w/v)

Camphor (w/v)

Phenol (w/v)

Ethanol (v/v)

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Benzyl alcohol (v/v) 7.02 3.3

Oleic acid (v/v) 5.27 2.5

Ethyl oleate (v/v) 3.51 1.6

Graph 1Solubility profile of rifampicin in 20% solution of individual solubilizers in castor oil

Table 4Equilibrium solubility data of rifampicin in mixed blends containing different solubilizers

Equilibrium solubilitySolubility

Blend enhancement(mg/ml)

ratioOB-1 18.00 8.5

OB-2 20.10 9.4

OB-3 15.27 7.2

OB-4 16.18 7.6

OB-5 12.03 5.6

OB-6 17.96 8.4

OB-7 11.05 5.2

Graph 2Solubility of rifampicin in mixed blends containing different solubilizers

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An approximate method of calculation wasused to determine the additive or synergisticeffect on solubility. The total strength of allsolubilizers was 20% w/v (constant) insolubilizer systems containing singlesolubilizer or combinations of foursolubilizers. (each solubilizer 5% w/v). Thesolubility of

rifampicin in this blend was found to be 20.10 mg/ml.The contributory solubility based on contribution of individual solubilizerfor blend OB-11 containing four solubilizers can be calculated a follows

–

The total contribution in solubility due to individual solubilizer present in blend

(Sum of solubilities in solutions

1= containing20%w/v of

individualsolubilizers)/4

1=

2=

Therefore,contributory solubilityof rifampicin in blendOB-2 was 6.85 mg/mlbut the observed

solubilityofrifampicin insameblendwas20.10mg/mlthisshowsthe

synergisticenhancement inthesolubility.

(ii) Accelerated stability

studies

Table 5Chemicalstability data of rifampicin in formulation OB-2

Graph 3Degradation curve forformulation OB-2

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Table 6Chemical stability data of rifampicin in formulation OB-3

Time % Drug remaining(days)

2-8 0C 25 0C0 100.0 100.0

7 99.5 99.5

14 98.8 98.5

21 98.3 98.1

28 98.0 97.1

Graph 4Degradation curve for formulation OB-3

Table 7Chemical stability data of rifampicin in formulation OB-7

Time % Drug remaining(days)

2-8 0C 25 0C 40 0C 55 0C0 100.0 100.0 100.0 100.0

7 99.6 98.7 91.4 82.6

14 99.1 99.1 85.3 71.4

21 99.1 97.8 80.6 58.4

28 98.3 97.4 75.8 47.1



Graph 5Degradation curve for formulation OB-7

Graph 6Arrhenius plot for formulation OB-2





The degradation constant (Table 8) and shelf lives of formulated rifampicin oily injections were calculated by using the degradation curves and Arrhenius plots.

Table 8

Kinetic data for various rifampicin injection formulations

k (day–1) x 100Temperature

OB-2 OB-3 OB-7

2-8 0C 0.05 0.05 0.0325 0C 0.07 0.05 0.0440 0C 0.41 0.56 0.4455 0C 0.80 0.81 1.15

The developed oilyinjection formulations ofrifampicin showed goodstability. The formulationOB-7 showed themaximum shelf life of 262

days, formulation OB-2 andOB-3 showed the shelf lives150 and 210 days

(iii)Effect of sunlight on drug degradation

respectivelyat roomtemperature. At thesame time,formulationswere alsofound to be

stablephysically inrespect ofcolour,precipitationandturbidity.

Table 9Light stability data for various developed injection formulations

FormulationTime (days)

code

OB-2

OB-3

OB-7

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From the table 9.10, it is evident thatlight caused degradation of rifampicin informulations (OB-2, OB-3 and OB-7).Maximum degradation was observed informulation OB-7 which was exposed tolight. The vials which were wrapped inaluminium foil

.

(iv)Effect of atmospheric oxygen on stability:

and placed in darkshowed lessdegradation ofrifampicin ascompared to thosewhich were exposedto direct sunlight. Formaximum stability offormulation, it shouldbe stored in darkplace and in ambercoloured vials

Table 10

Effect of oxygen on stability of formulations OB-11 and OB-12

Percent residual drug in formulationFormulation

Time (days) Oxygen removed Oxygen presentcode (Flushed with (Not flushed

nitrogen) with nitrogen)0 100.0 100.07 99.3 98.4

14 98.7 97.1

OB-2 21 97.7 95.528 97.1 93.20 100.0 100.07 99.7 99.4

OB-3 14 98.9 97.221 97.9 96.228 96.4 95.1

From the table 10, it isevident that in case offormulation OB-2, thevials from whichoxygen was removedcontained moreresidual drug at end of28 days (97.1%) ascompared to vialswhich containedoxygen (93.2%), so itcan be concluded thatatmospheric oxygencause degradation ofdrug in formulation.

From the studyof formulation OB-3, itwas observed that theboth sets of vials i.e.flushed with nitrogenand not flushed withnitrogen contained

almostsameamount ofresidualdrug(96.4% incase offlushedvials and95.1% incase ofvials whichwere notflushed). Itcan beexplainedon thebasis oftheircomposition,formulation OB-2contained

oleic acid,phenol,benzylalcoholandethanol.Formulation OB-3containedphenol,thymoland oleicacid. Fromtheliterature itwasknownthatthymolhad someantioxidant

properties so therewas almost noeffect of oxygen onformulationcontaining thymol.

CONCLUSION

The resultsof solubility studiesrevealed that therewas appreciableenhancement insolubility of poorlysoluble drugrifampicin whenthe oilsoluble/miscibleadditives wereadded. Thesynergisticenhancementswere alsoobserved in the

blendseq. inblendOB-2 thesolubilityof drugwasfound tobe 20.10mg/mlwhile thecontributorysolubilitydue toindividualsolubilizerpresentin blendwasfound tobe 6.85mg/ml

thisshowedthesynergisticenhancement insolubility.In thisway, thetoxicityissuesrelatedto thesolubilizers usedwereminimized as theindividualsolubilizers

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concentration in blends was reduced. Thepharmaceutical industries have broadvarieties of safe chemicals and these canbe used to increase the solubility of poorlysoluble drug (may be in water/oil or in anyother liquid) by proper application of mixedsolvency concept. In such case, when theselected solubilizers were safe and used inless concentrations (made possible byapplication of mixed

solvency) thedesired solubility canbe achieved anddosage forms can bedeveloped which areexpected to be freeof toxicity issues orrarely may producevery low risk of anytoxicities. The resultsof stability studysupported that the

formulationsdeveloped by novelapplication of mixedsolvency conceptshad desirablestability also.

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