DOE for Extended Release

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PHARMAGENE Vol: 1 Issue: 2

Optimization of Formulation Variables of Ranolazine Extended-Release

Tablets by 32Full Factorial Design

Shah Pranav*, Naik Bhargavi, Zalak Chandarana

Maliba Pharmacy College, Bardoli, Gujarat

ABSTRACT

Ranolazine is antianginal drug, approved by US FDA in 2006. It is marketed as extended release tablets (Ranexa 500mg/1gm).

Ranolazine is extensively metabolized in the liver and its absorption is highly variable. The present study was aimed to applyexperimental design in the development and optimization of drug release from extended release matrix tablets of Ranolazine(antianginal drug) using two factor three level (32) full factorial design. The extended release matrix tablets of Ranolazine were

formulated using pH dependent polymer (Eudragit L 100-55), Sodium hydroxide, MCC, HPMC 5 cps and Magnesium stearate.

The amount of independent variables, Eudragit L100-55 (X1) and Sodium Hydroxide (X2) were optimized on the basis of drug

release profiles at 0.5, 4, 12, 24 hours (dependent variables ) of different tablets batches as per 32 full factorial design. Tabletswere prepared by wet granulation technique and evaluated for various physicochemical parameters and in vitro drug release.Polynomial equations and contour plots derived from the data obtained from 13 batches were used to predict the values of

independent variables and their effect on dependent variables for the formulation of optimized tablets with desired properties.

Optimized formulation from DOE had identical dissolution profile (f2 = 85.95 and f1 = 2.29) with innovators tablet. Stability

studies of optimized batch were conducted at accelerated conditions for three months and tablets were found to be stable. Thus

the study revealed that experimental design could efficiently be applied for optimization of amount of excipients affecting drug

release. Also, it is an economical way of obtaining the maximum amount of information in a short period of time and with the

few experiments.

KEY WORDS: Ranolazine extended release tablet, Experimental design, Full Factorial Design,

Received on 03-05-2013 Modified on 04-06-2013 Accepted on 10-06-2013

INTRODUCTION

Oral administration of drugs is strongly preferred because

of its convenience, relatively low production cost and the

high level of patient safety. However there are someproblems associated with the oral drug delivery such as

poor bioavailability , high first pass metabolism, frequent

drug administration etc. Extended-release systems allow

the drug to be released over prolonged time periods. Byextending the release profile of a drug, the frequency of

dosing can be reduced. Extended release can be achieved

using sustained or controlled release dosage forms [1].

*Address for correspondence:

Dr. Pranav Shah, Professor,

Maliba Pharmacy College, Bardoli, Gujarat, India

Email:pranav.shah@ut u.ac.in

The oral extended release system shows a typical pattern of

drug release in which the drug concentration can be

maintained in the therapeutic window for a prolongedperiod of time (extended release), thereby ensuring

controlled t herapeutic action.

Ranolazine is antianginal drug, approved by US FDA in2006. It is marketed as extended release tablets (Ranexa

500mg/1gm). Ranolazine is extensively metabolized in the

liver and its absorption is highly variable. The apparentterminal half-life of Ranolazine is 7 hrs. Ranolazine has

relatively high solubility (42.08 mg/ml in 0.1 N HCl) at low

pH in the stomach (pH 1.2 3). The high acid soluble

property of ranolazine results in rapid drug absorpt ion and

clearance, causing large and undesirable fluctuations in

PHARMAGENEVol: 1 Issue: 2

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ISSN-2321-0966 (Print) ISSN-2321-0974 (Online)

Research rticle


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plasma concentration of ranolazine and short duration of

action, thus necessitating frequent oral administration for

adequate treatment [2]. The present study was aimed to

develop a matrix tablet using pH-dependent polymer whichis insoluble at low pH and begins to dissolve at about pH >

5. The extended release tablets were formulated using pH

dependent polymer (Eudragit L 100-55), pH independent

binder (HPMC 5 cps) and sodium hydroxide as neutralizing

agent. Sodium hydroxide facilitates the conversion of the

Eudragit L 100-55 into the latex like film formed around

the individual granules which controls the drug release

from the formulation above pH 4.5 [3].Statistical experimental design methodologies are

powerful, efficient and systematic tools in the design of

pharmaceutical dosage forms, allowing a rationalistic study

of the influence of formulation and/or processing

parameters on the selected responses with short experiment

time and improvement in the research and development

work [4-6]. The main objective of the experimental design

strategies is to plan experiments in order to obtain themaximum information regarding the considered

experimental domain with the lowest number of

experiments [7]. Moreover, the multi-variant strategy of

experimental design enables the simultaneous evaluation of

the influence of the different variables involved in any

process, being therefore part icularly useful when, as in the

case of pre-formulation studies, multiple factors have to beevaluated simultaneously.

In particular, optimization by means of statistical

experimental design methodologies has been successfully

applied in the development of different kinds of modified

release dosage forms, allowing a quick and efficient

quantification and prediction of the effects of formulationchanges on t he considered crucial responses [8-13].

MATERIALS AND METHODS

Materials

Ranolazine was purchased from Virdev Intermediates,

Surat, India. Eudragit L 100-55 was obtained from Evonik

Industries, Germany. Microcrystalline cellulose was

purchased from FMC Biopolymer, India. HPMC 5cps was

purchased from Colorcon, Goa, India. Sodium hydroxidewas purchased from Cadila Pharmaceutical Ltd., Dholka,

India and Magnesium stearate was purchased from Skant

Healthcare Ltd., M umbai, India.

Experimental Design

Two factor three level (32) full factorial design was

employed for development of ranolazine extended release

matrix tablets. A translation of coded values of independentvariables and experimental design is executed as in t able 1.

Independent variables were as follow:

X1 : Amount of Eudragit L 100-55 (mg/tab)

X2 : Amount of Sodium hydroxide (mg/tab)

Dependent variables evaluated were as follows:

Y1 = % drug released in 0.5 hours

Y2 = % drug released in 4 hours



Preformulation studiesPreformulation studies were designed to identify

physicochemical properties of Ranolazine and excipients

that may influence formulation design and method of

manufacture.

Table 1: Execution of experimental design and coding

of actual values of independent variables for factorial

design

Batch Level of Factor

X1

Amount of

Eudragit L 100-55 (mg/tablet)

Level of Factor

X2

Amount of

Sodiumhydroxide

(mg/tablet)

F1 -1(67) -1(2.6)

F2 0(83.50) -1(2.6)

F3 +1(100) -1(2.6)

F4 -1(67) 0(3.9)

F5 0(83.50) 0(3.9)

F6 +1(100) 0(3.9)

F7 -1(67) +1(5.2)

F8 0(83.50) +1(5.2)

F9 +1(100) +1(5.2)

F10* 0(83.50) 0(3.9)

F11* 0(83.50) 0(3.9)

F12* 0(83.50) 0(3.9)

F13* 0(83.50) 0(3.9)

*Centre point batches

Analytical method development

HPLC method was developed to perform assay and

analysis of dissolution samples of Ranolazine. HPLCanalysis of samples were done using Phenomenex Luna

ODS 250 mm 4.6 mm, 5 microns column with mobile

phase flow rate 1.0 ml/min. Mobile phase consist of buffer

pH 7.5 and acetonitrile in the ratio of 40:60. Sample andstandards were dissolved in mobile phase and detected

using UV detector at wavelength 225nm. Fig. 1 shows the

HPLC chromatogram of standard ranolazine (100g/ml)

with retention time of 8.487 minutes.


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Preparation of tablets

Tablets were prepared by wet granulation technique. Each

batch of tablets (F1F13) (Table 2) has varied amount of

Eudragit L100-55 and sodium hydroxide. All ingredientswere weighed accurately in required quantity. Ranolazine,

Eudragit L 100-55, Avicel PH 101 and HPMC 5 cps were

sifted through 20# sieve. The materials were mixed in r apid

mixer granulator (RMG) at 75 rpm impeller speed. Binder

solution was prepared by dissolving sodium hydroxide in

sufficient amount of water. Granulation was done in RMG.

The wet mass was dried in FBD at 60C for 20 minutes and

the semi dried mass was passed through 16# and further

dried at the same temperature till LOD value below 2% wasobtained on moisture balance. The dried granules were

passed through 16# sieve. Sized granules were then mixed

with previously sifted magnesium stearate (60#) for 3

minutes. The tablets were compressed with 16.4 8 mm

capsule shaped, standard concave punches with break line

on one side and plain on other side (D tooling).

Table 2: Formulation of tablets batches

Ingredients

(mg)

Batches

F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12 F13

Ranolazine* 506 506 506 506 506 506 506 506 506 506 506 506 506

EudragitL 100-55

67 83.5 100 67 83.5 100 67 83.5 100 83.5 83.5 83.5 83.5

HPMC 5 cps 13 13 13 13 13 13 13 13 13 13 13 13 13

SodiumHydroxide

2.6 2.6 2.6 3.9 3.9 3.9 5.2 5.2 5.2 3.9 3.9 3.9 3.9

Magnesium

Stearate

13 13 13 13 13 13 13 13 13 13 13 13 13

MCC PH 101 58.4 41.9 25.4 57.1 40.6 24.1 55.8 39.3 22.8 40.6 40.6 40.6 40.6

Total tablet

weight

660 660 660 660 660 660 660 660 660 660 660 660 660

* The potency of Ranolazine was found to be 506 mg for actual dose of 500 mg/tablet; LOD: 0.29%; Assay: 99.1%

Figure 1: Chromatogram of standard Ranolazine (100g/mL) (Retention time: 8.487 min)

Assay

Assay of ranolazine was done using HPLC method.Standard solution was prepared by dissolving 50 mg of

Ranolazine standard in 50 ml mobile phase in volumetric

flask. Tablet powder equivalent to 50 mg of ranolazine was

accurately weighed and transferred into 50 ml volumetric

flask containing 25ml mobile phase (Buffer:Acetonitrile;

40:60), sonicated for 30 minutes, allowed to cool to room

temperature and diluted upto 50ml volume with mobilephase and mixed. Resulting solution was filtered through

0.45 m PVDF Millipore filter discarding first few ml of

the filtrate. 5.0 ml of clear filtrate was diluted to 50.0 ml

with mobile phase and mixed. 20L of sample and standard

preparation were injected into the column. Chromatogram

was recorded and the response was measured at 225nm.

(Figure: 1) Content of ranolazine per tablet was calculated.

I n vitro drug release study (I n vi tro dissolution study) [14]

In vitro drug release study was performed as per the

following specifications of OGD, 900 ml of 0.1 N HCl

medium at 50 rpm for 24 hours at 370.5 C. A 10 ml of

sample from dissolution medium was withdrawn at

predetermined time intervals (0.5, 2, 4, 8, 12, 20, 24 hours)

and replaced by an equal volume of dissolution medium.

The samples were filtered through 0.45m whatman filterpaper and 5.0 ml of filtrate was diluted to 20.0ml with

dissolution medium. Samples were analyzed using HPLC.

Mechanism of drug release [15-17]

To evaluate the mechanism of drug release from the dosage

form, data for the first 60% of drug release were plotted in

Korsmeyers equation as log cumulative percentage of drug


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Optimization of Formulation Variables of Ranolazine Extended-Release Tablets by 32Full Factorial Design

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released vs log time, and the exponent n was calculated

from the slope of the straight line.

/ = Where, Mt/M is the fractional solute release, t is the

release time, K is a kinetic constant characteristic of the

drug/ polymer system, and n is an exponent that

characterizes the mechanism of release.

Stability Study

The optimized formulation was subjected to short term

accelerated stability study (40C/75% RH) for the period of

three months as per ICH guidelines. Physical stability was

analyzed by recording the change in appearance, hardness,friability and chemical stability was analyzed by the change

in the assay and in vitro drug dissolution at the end of three

months.

RESULTS AND DISCUSSION

Preformulation studies

Ranolazine was found to have very poor compressibility

and flow properties (Carrs index: 36.67, Hausners ratio:

1.5789), hence wet granulation method was opted for better

compression and good flow property for the preparation of

the Ranolazine matrix tablet.

Precompression evaluation of granules exhibited good flow

property (Hausners ratio < 1.25) and good compress ibility

(Carrs index < 20%). Post compression evaluation of

tablets such as appearance, dimensions, weight variation,

hardness, friability, and assay were within thespecifications (Table 3).

Table 3: In process quality control of Tablets

Batch

Average

tablet weight

(mg)

n = 20

Hardness

(kg/cm2)

n = 10

Dimensions

n = 6 % Friabil ity Assay

n = 5Length

(mm)

Width

(mm)

Thickness

(mm)

F1 662.62.88 17.20.5 16.400.01 8.010.02 5.710.02 0.064 99.800.10

F2 659.22.38 17.50.2 16.420.01 8.020.01 5.720.01 0.073 98.320.20

F3 663.13.27 17.80.4 16.390.03 8.010.03 5.750.03 0.068 100.440.23

F4 661.42.25 17.40.3 16.410.01 7.990.03 5.840.01 0.066 99.600.33

F5 658.52.60 17.30.1 16.380.03 7.980.02 5.770.02 0.055 99.210.19

F6 660.32.96 17.30.1 16.410.03 8.010.03 5.850.01 0.062 98.680.22

F7 662.63.20 17.40.4 16.420.04 7.990.01 5.740.01 0.059 100.340.30

F8 659.82.49 17.30.2 16.380.02 8.030.01 5.720.03 0.053 100.810.36F9 658.22.31 17.10.4 16.410.03 8.020.02 5.810.01 0.056 99.480.20

F10 662.62.84 17.80.4 16.430.01 8.010.02 5.710.03 0.073 99.610.33

F11 659.22.58 17.40.3 16.420.02 8.010.01 5.730.01 0.068 99.210.19

F12 663.12.99 17.30.1 16.390.01 8.020.03 5.760.02 0.066 98.680.22

F13 661.42.34 17.10.1 16.410.03 7.980.01 5.790.01 0.055 100.340.30

I n vitro drug release study (I n vitro dissolution)

In v itrodrug release data (Figure 2) showed that the drug

release from all the formulated batches (F1-F13) (n = 3)

was extended upto 24 hours.

Figure 2: Comparative % cumulative drug release

profile of formulations (F1F13)


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(a)

(b)

(c)

(d)Figure 3: Linear correlation plots of dependent variables Y1-Y4 (a-d) between actual and predicted value

Drug Release kinetics

Dissolution data were fitted to zero order, first order,Higuchi and Korsmeyer kinetic treatment for all the

formulations and different kinetic equat ions were app lied to

interpret the release rate. The formulation with higher

correlation coefficient R2 was found with Higuchis Model

as shown in Table 4 indicating that release from gel

forming system is based on diffusion mechanism for allformulations. The value of release exponent was more than

0.45 and less than 0.798 indicating non-fickian anomalous

release from all the formulations except F1.

Statistical Analysis

The two factor three level full factorial design allowed the

development of mathematical equations, where predictedresults (Y) were assessed as a function of amount ofEudragit (X1) and amount of Sodium hydroxide (X2) and

calculated as the sum of a constant, two first-order effects

(terms in X1 and X2), one interaction effect (X12) and two

second-order effects (X12and X22).

The relationship between the two independent variables

(amount of Eudragit L 100-55 and sodium hydroxide) and

the four dependent variables (% drug release at 0.5, 4, 12

and 24 hour) were analyzed using response surfacemethodology

Data given in Table 5 depicts that all the models were

significant at the 5% confidence level since P values were

less than 0.05. The large P values for lack of fit (>0.05)

presented in T able 5 (PLOF) show that theF-statistic was

insignificant, implying significant model correlationbetween the variables and process responses. Adequate

Precision (AP) values higher than four (Table 5) for all the

responses confirmed that all predicted models can be used

to navigate the design space defined by the full factorial

design. For all the models % CV were not greater than 10%

(Table 5) which indicate that models are reproducible.

Model equation for the all the variables showed thenegative co-efficient terms for the first order effect,interaction term and second order effects which indicated

the negative effect on the response with respect to the

independent variable.

Contour Plots and Response Surface Analysis

Figure 4, 5, 6 and 7 (a and b) represents the response

surface plot and contour plot of dependent variables Y1, Y2,


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Y3 and Y4 respectively. For responses Y1, Y2, Y3 and Y4

drug release decreases rapidly with increase in amount of

one variable while other at low level. This showed that both

the variables (Eudragit L 100-55 and sodium hydroxide)had prominent negative effect on Y1, Y2, Y3 and Y4.These

results are in confirmation with mechanism.

As the concentration of pH dependent binder increases in

the formulation, there is decrease in the release rate of

ranolazine at pH below 4.5 as enteric coating formed by the

binder was less soluble in acidic pH. Partial neutralizingagent, sodium hydroxide facilitated the conversion of the

binder into the latex like film formed around the individual

granules which controled the drug release from the

formulation above pH 4.5.

Table 4: Release kinetic data for F1-F13 formulations

Batch no. Zero order

kinetic R2

First order

kinetic R2

Higuchi

kinetic R2

Korsmeyer Peppas

R n

F1 0.868 0.888 0.984 0.976 0.426

F2 0.928 0.954 0.993 0.997 0.452

F3 0.951 0.958 0.993 0.998 0.604

F4 0.882 0.885 0.991 0.997 0.453

F5 0.895 0.97 0.994 0.997 0.465

F6 0.972 0.936 0.981 0.996 0.707F7 0.92 0.959 0.997 0.998 0.485

F8 0.913 0.973 0.996 0.997 0.499

F9 0.99 0.939 0.95 0.998 0.798

F10 0.895 0.972 0.994 0.997 0.458

F11 0.891 0.932 0.993 0.997 0.458

F12 0.898 0.969 0.994 0.997 0.463

F13 0.895 0.964 0.994 0.997 0.455

Table 5: ANOVA analysis of data

ANOVA results for dependent variablesY Mathematical

model

P value PLOF R Adjusted

R2

Predicted

R2

AP S.D CV

%

PRES

S

Y1 Y1= +16.01-5.75X1-2.56X2 + 4.49X12-4.01X1

2-0.74X22


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Figure 4: Response surface plot (a) and Contour plot (b)

for response Y1


for response Y2


for response Y4


for response Y3


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Optimization

After generating the model polynomial equations to relate

the dependant and independent variables, the process wasoptimized for all four responses. The final optimal

experimental parameters were calculated using Design-

Expert V8 (8.071).

The optimized batch F14 contains:

Amount of Eudragit L 100-55 (X2) : 80 mg/tab

Amount of NaOH : 3.25 mg/tab

Dissolution profile of Ranexa (innovators formulation) and

optimized formulation F14 were compared using the FDA

recommended similarity factor (f2) (figure 8). The value of

f2 was found to be 85.95 which was above the critical value

(50) indicating an equivalence to the release profile of theoptimum formulation and the innovator p rofile.

Figure 8: Dissolution profile comparison of optimized

batch and innovators product

Figure 9: Overlay plot of optimized batch

Stability study

Stability study of the optimized formulation proved the

physical and chemical integrity of the developed ranolazine

extended release matrix tablet with no significant change in

the assay and dissolution profile.

Validation of Response Surface Methodology

Five check point batches were formulated for the validation

of response surface methodology. Actual experimentalresponses and predicted responses were then compared to

validate design (Table 6). For all the 5 checkpoint

formulations, the results of the dependent variables were

found to be within limits. For validation of RSM results,

the experimental values of the responses were compared

with the anticipated values and the prediction error was

found to vary between -5.62 and +5.17. These results

demonstrate the reliability of the optimization procedure inpredicting the effect of process variables on the dissolution

behavior of the ranolazine extended release tablet p rofile.

Table 6: Composition of check point batches and

comparison of experimental and predicted values of

response variables

Check pointFormulations

Response

Variabl

es

Experi

mental

values

Predict

ed

values

%predicti

on

ErrorX1 X2

67.83 2.96

Y1 19.14 19.65 -2.70

Y2 49.63 48.66 1.94

Y3 76.8 77.62 -1.07

Y4 98.48 97.09 1.40

87.62 3.12

Y1 16.37 15.52 5.17

Y2 44.03 42.57 -3.29

Y3 70.65 71.72 -1.51

Y4 90.57 95.66 -5.62

71.95 4.81

Y1 14.93 15.67 -4.99

Y2 43.61 42.31 2.96

Y3 70.99 70.14 1.19

Y4 95.55 93.29 2.35

76.90 4.55

Y1 15.88 16.10 -1.41

Y2 42.42 42.86 -1.03

Y3 72.35 71.04 1.79

Y4 96.06 94.08 2.05

83.50 2.60

Y1 17.56 17.83 -1.53

Y2 45.18 45.90 -1.57

Y3 76.36 75.37 1.31

Y4 94.30 96.80 -2.59

CONCLUSION

Ranolazine extended release tablets were manufactured by

wet granulation technique. The tablets exhibited drugrelease for a period of 24 hours and followed Higuchi

kinetics. The amount of Eudragit L100-55 and Sodium

hydroxide was optimized by 32 full factorial design based

on the drug release. The contour plots represented the

influence of the amount of the independent variable on the


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drug release. The design was also validated by the check

point batches. The optimized formulation exhibited drug

release similar to the innovator (f2= 85.95). The accelerated

stability studies suggested no significant change in the drugcontent, physical properties and drug release.

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