Research Article Optimization of Glipizide sustained release matrix tablet formulation by central composite design- response surface methodology Parasuram Rajam Radhika* 1, Tapan kumar Pal 1, Thangavel Sivakumar 2. *1 Bioequivalence Study Centre, Department of Pharmaceutical Technology, Jadavpur University, Kolkata, India-700 03 2 Nandha College of Pharmacy and Research Institute, Koorapalayam Pirivu, Erode, Tamilnadu, India- 638052. For correspondence:parasuram Rajam Radhika,Bioequivalence Study Centre, Department of Pharmaceutical Technology, Jadavpur University, Kolkata, India-700 03 E-mail:radhi_kannan2005@yahoo.co.in Received on:14-09-2008; Accepted on :08-12-2008 ABSTRACT The aim of the present study was to design an oral sustained release matrix tablet of Glipizide and to optimize the drug release profile using response surface methodology. Tablets were prepared by wet granulation method using HPMC K 100 and Eudragit L 100 as matrix forming polymers. A Central composite design for 2 factors at 3 levels each was employed to systematically optimize drug release profile. HPMC K 100 and Eudragit L 100 were taken as the independent variables. The dependent variables selected were % of drug released in 2 hrs (rel 2 hrs), % of drug released in 8 hrs (rel 8 hrs), and % of drug released in 12 hrs (rel 12hrs). Contour plots were drawn and optimum formulations were selected by feasibility and grid searches. The formulated tablets exhibited Non fickian drug release kinetics approaching Zero order as the value of release rate exponent (n) varied between 0.6024 and0.7354, resulting in regulated and complete release until 24 hrs. The polymer HPMC K 100 and Eudragit L 100 had significant effect on the drug release from the tablets (P<0.05). Polynomial mathematical models, generated for various response variables using multiple linear regression analysis, were found to be statistically significant (P<0.05).Validation of optimization study performed using 8 confirmatory runs indicated very high degree of prognostic ability to response surface methodology, with percentage error varied between -0.0132 and 0.7566. Besides unveiling the effect of the 2 factors on the various response variables, the study helped in finding the optimum formulation with sustained drug release. Key words: Sustained Release: Matrix Tablet, Hydroxy propyl methyl cellulose (HPMC K 100), Eudragit L 100, and Central Composite Design. INTRODUCTION Sustained or controlled release delivery systems can achieve predictable and reproducible release rates, extended duration of activity for short half life drugs, decreased toxicity, and reduction of required dose, optimized therapy and better patient compliance. Matrix type sustained delivery systems are popular because of their ease of manufactures. It excludes complex production procedure such as coating and pellitization during manufacturing and drug release from the dosage form is controlled mainly by the type and proportion of the polymers used in the preparation. Hydrophilic polymer matrix is widely used for formulating a sustained release dosage form (1-4). Hydrophilic polymer matrix system are widely used for designing oral sustained release delivery systems because of their flexibility to provide a desirable drug release profile, cost effectiveness, and broad regulatory acceptance. The hydrophilic polymer selected for the present study was HPMC K- 100. HPMC K 100 forms transparent tough and flexible films from aqueous solution. The films dissolve completely in the gastrointestinal tract at any biological ph and provide good bioavailability of the active ingredient.eudragit L 100 was also used along with the HPMC K-100 to get the required sus- 94
tained release of the drug. Glipizide is widely used sulphonyl urea antidiabetic agent, adjunct to diet to the management of type 2 (Non insulin dependent) diabetes mellitus in patients whose hyperglycemia cannot be controlled by diet and exercise alone. Glipizide stimulates insulin secretion from the β cells of pancreatic islets tissue, increases the concentration of insulin in the pancreatic vein and may increase the number of insulin receptors (5). It is a weak acid (pka = 5.9) practically insoluble in water and acidic environment but highly permeable (class 2) according to the Biopharmaceutical Classification System (BCS) (6). The oral absorption is uniform, rapid and complete with a bioavailability of nearly 100% and an elimination half-life of 2 4 h (6). Glipizide is reported to have a short biological half-life (3.4 ± 0.7 h) requiring it to be administered in 2 to 3 doses of 2.5 to 10 mg per day (7). Sustained release formulations that would maintain plasma levels of drug for 8 to 12 hrs might be sufficient for once a day dosing for Glipizide. SR products are needed for Glipizide to prolong its duration of action and to improve patient compliance. In development of a sustain release tablet dosage form, an important issue is to design an optimized formulation with an appropriate dissolution rate in a short time period and minimum number of trials. For this purpose, a computer based optimization technique with a response surface methodology (RSM) is widely practiced in the development and optimization of drug delivery devices. Based on the principal of design of experiments, the methodology encompasses the use of various types of experimental designs, generation of polynomial equations, and mapping of the response over the experimental domain to determine the optimum formulations. The technique requires minimum experimentation and time, thus proving to be far more effective and cost effective than the conventional methods of formulating dosage forms. The current study aims at developing and optimizing a sustained release matrix tablet of Glipizide using HPMC K-100 and Eudragit L 100 by wet granulation method and optimizes the formulation using RSM. Use of the response surface methodology has been proved to be a useful tool in the development and optimization (8). Different steps involved in response surface methodology include experimental design, regression analysis, constraint optimization and validation. MATERIALS AND METHODS MATERIALS: Glipizide, HPMC K-100, Eudragit L-100, were received as Gift sample from Aravind Remedies (AR), Chennai. Graph. Lactose, Povidone, Iso Propyl Alcohol (IPA), Aerosil, Magnesium Stearate, was of AR Grade. METHODS: Preparation of Sustained Release Matrix Tablets Table1enlists the composition of different sustain release formulations prepared using varying amounts of the polymers (HPMC K 100 and Eudragit l 100) and granulated using Povidone in Iso- propyl alcohol along with the fixed quantity of magnesium stearate as the lubricant. Drug and the excipient were homogeneously blended and subsequently compressed using double punch tabletting machine, equipped with beveled flat punch 8/32 mm, diameter (Cad mach Machinery Co: Ahemedabad, India) Experimental Design: A central composite design (CCD) with a= 1 was employed as per the standard protocol(10, 11).The amounts of HPMC K 100 ( ) and Eudragit L 100 ( ) were selected as the factors, studied at 3 levels each. The central point (0, 0) was studied in quintuplicate. All ot6her formulation and processing variables were kept invariant throughout the study. Table 2 summarizes an account of the 13 experimental runs studied, their factor combination and the translation of the coded levels to the experiment units employed during the study. % of drug released in 2hrs ( rel 2 hrs ) ( Y 1 ), % of drug released in 8 hrs ( rel 8hrs ) ( Y 2 ), % of drug released in 12 hrs ( rel 12 hrs ) ( Y 3 ) were taken as the response variables. Tablet assay and Physical Examination 10 tablets were taken and the drug was extracted using methanol and the samples were analyzed spectrophotometrically (Shimadzu Model 1601) at 276 nm. Tablets were also evaluated for hardness (n=10), Friability (n=10), Weight Variation (n=10) and thickness (n=10). Invitro Drug Release Studies Dissolution studies were performed for all the formulation combinations, in triplicate, determined using USP 22 type I dissolution apparatus ( Electro lab, TDT- 08 L ) where 900 ml of 0.1 N HCl and phosphate buffer of ph 6.8 were used as dissolution media maintained at 37 o C ( ± 0.5 o c ) at 50 rpm. The release rates from the tablets were conducted in the dissolution medium of 0.1 N HCL for 2 hours and thereafter in phosphate buffer of ph 6.8. 5 ml of aliquot were withdrawn at 2, 4, 8, and 12 hours with replacement of fresh media. Solution samples were analyzed by using UV- Spectrophotometer (Shimadzu Model 16010) at 276 nm. Drug release profiles were drawn using MS-Excel Software and the values were obtained by interpolation from Excel 95
Table 1 Composition of 10 mg Glipizide Sustained Release Matrix Tablets Ingredients Amount (mg) Glipizide 10 HPMC K-100 50-70 Eudragit L 100 50-70 Povidone 10 Aerosil 1 Iso Propyl Alcohol 100 Magnesium Stearate 2 Lactose q.s to 173 mg Table 2 Factor combination as per the chosen experimental design Trial No: Coded factor levels. I II III IV V VI VII VIII IX X XI XII XIII Translation of coded levels in actual units Coded level -1 0 1 HPMC K 100 (mg) 50 60 70 Eudragit L 100 (mg) 50 60 70 Table 3: Drug Release Parameters of Various Trial Formulations Prepared as per the Experimental Design Trial No Factor amount (mg) rel 2hrs(%) rel 8hrs(%) rel 12hrs (%) n r2 1 60 60 14.74 56.23 85.56 0.6889 0.9962 2 50 70 16.54 68.95 95.37 0.6024 0.9735 3 50 50 17.18 78.46 98.45 0.7037 0.9943 4 70 70 21.45 68.85 99.65 0.6947 0.9946 5 70 50 20.54 81.24 98.56 0.6282 0.9769 6 60 60 14.75 55.54 82.25 0.7354 0.9822 7 60 50 14.76 54.52 84.34 0.6273 0.9527 8 70 60 20.54 58.59 100.20 0.6414 0.9639 9. 60 60 14.75 56.38 82.54 0.6984 0.9918 10 60 60 14.75 55.54 85.56 0.6980 0.9918 11 60 70 14.78 55.29 84.34 0.6806 0.9786 12 50. 60 17.18 78.98 98.40 0.6935 0.9934 13 60 60 14.76 56.38 84.35 0.7000 0.9927 =HPMC K100, = Eudragit L 100, rel 2 hrs = Release in 2 hours, rel 8 hrs =Release in 8 hrs, rel 12 hrs = Release in 12 hrs, n= Release component obtained from Koresmeyer Equation, r 2 = regression coefficient. 96
Table 4: Analysis of variance (ANOVA) for all three Responses rel 2hrs (Y 1 ) rel 8 hrs (Y 2 ) rel 12 hrs (Y 3 ) Source F p-value F p-value F p- value Model 11.28 3213 179.69 28.33 96.20 40.45 A 16072.58 <01 32.77 23 0.68 0.4468 B 0.57 0.4845 0.047 0.8374 0 0 AB 710.17 <01 0.33 0.5922 1.83 0.2343 A 2 1.343 <01 111.54 01 243.63 <01 B 2 14.49 0.0125 1.94 0.2198 0.26 0.630 A 2 B 12.55 0.0165 7.22 0.0435 0.14 0.7248 AB 2 570.06 <01 24.82 42 0.022 0.8882 Significant effect (p value < 0.5) of factors on individual responses is shown in bold, rel 2hrs: Release in 2 hrs, rel 8hrs: Release in 8 hrs, rel 12 hrs: Release in 12 hrs, A- HPMC K 100, B- Eudragit L 100. Table 5:Composition of the Checkpoint Formulations, the Predicted and Experimental Values of Response Variables, and Percentage Prediction Error S. No. 1. 2. 3. 4. 5. 6. 7. 8. Composition HPMCK100 : Eudragit L100 60:50 60:70 50:50 50 : 60 70:50 50:70 60:60 70:70 Response Variable Experimental value Predicted value Residual Rel 2 hrs Rel 8 hrs Rel 12 hrs 14.74 56.23 85.56 14.54 68.95 85.37 14.28 78.46 88.45 14.76 56.38 84.35 14.54 71.24 88.56 14.75 55.54 82.25 14.76 54.52 84.34 14.75 55.54 85.56 14.71 55.34 84.22 14.52 69.12 85.54 14.25 78.95 87.93 14.74 56.45 84.60 14.49 71.76 88.54 14.89 55.75 83.03 14.84 54.86 84.71 14.83 55.49 85.47 0.2039-0.1952 0.1866 0.1377-0.2459-0.1987 0.2105-0.6206 0.5913 0.1356-0.124-0.2955 0.3450-0.6360 0.0225-0.9402-0.3766 0.2682 0.4219-0.6197-0.4368-0.5394 0.0901 0.1053 97
Cumulative Percentage Release 100 90 80 70 60 50 40 30 20 10 0 0 2 4 6 8 10 12 Time in Hours 60:60 55:55 65:55 65:65 55:65 12.1:37.4 1.95:9.90 1.10:33.15 37.95:32.4 32.4:49.20 Fig 1 Cumulative Glipizide Release (%) verses Time profiles for glipizide matrix formulation prepared as per the experimental design. Each value represents the mean ±S.D, n= 13 Rel 2 hrs Design Points 21.45 14.74 Rel 2 hrs Rel 2 hrs Design points above predicted value Design points below predicted value 21.45 14.74 21.5 X2 = 16.7719 19.1069 15.6045 5 15.6045 17.9394 X2 = Rel 2 hrs 19.725 17.95 16.175 14.4 - - - - Fig- 2 Response surface plot and corresponding contour plot showing the relationship between various levels of polymer AA (HPMC K 15) and BB (Eudragit L 100) on drug release in 2 Hrs 98
Rel 8 hrs Design Points 81.24 54.52 Rel 8 hrs 62.9508 Rel 8 hrs Design points above predicted value Design points below predicted value 81.24 54.52 82 X2 = 67.6973 62.9508 58.2044 72.4437 5 58.2044 X2 = Rel 8 hrs 74.75 67.5 60.25-62.9508 67.6973 53 72.4437 - - - Figure 3. Response surface plot and corresponding contour plot showing the relationship between various levels of polymer AA (HPMC K 15) and BB (Eudragit L 100) on drug release in 8 Hrs Rel 12 hrs Design Points 100.2 82.25 X2 = - Rel 12 hrs 91.8179 86.4147 89.1163 5 94.5194 94.5194 86.4147 91.8179 89.1163 Rel 12 hrs Design points above predicted value Design points below predicted value 100.2 82.25 X2 = Rel 12 hrs 101 96.25 91.5 86.75 82 - - - Fig 4: Response surface plot and corresponding contour plot showing the relationship between various levels of polymer AA (HPMC K 15) and BB (Eudragit L 100) on drug release in 12 Hrs. 99
(A) (B) 2 hr 2 hr predicted value 25 20 15 10 5 0 0 5 10 15 20 25 experimental value Residual value - 0 10 20 30-1.50 Experimental value (C) (D) 8 hr 8 hr Predicted released in 8 hrs (%) 80 60 40 20 0 0 20 40 60 80 Experimental release in 8 hrs (%) Residual value - 0 50 100 Experimental value (E) (F) 12 hr 12 hr 120 100 80 60 40 20 0 0 10 20 30 40 50 60 70 80 90 100 110 experimental value Residual value 0.60 0.40 0.20-0.20-0.40-0.60 0 50 100 150 Experimental value Fig 5. Linear Correlation Plots (A, C, E) between Experimental and Predicted Values and the Corresponding Residual Plots (B, D, F) for various variables. Drug Release Kinetics In order to investigate the model of release from tablets, the drug release data of the formulation was analyzed with the following models, Q = K o t ( Zero Order kinetics ), ln (100 q ) = ln Q o K t ( first order kinetics ), Q= K t ( Higuchi Model ) and Koresmeyer etal s equation(12) Log ( Mt/ M& ) = log K + nlog t. where Mt is the amount of the drug release at time t, M& is the amount of drug release after infinite time, K is a release rate constant and n is the diffusion exponent indications of the drug release mechanism. Optimum Release Profile Optimum release profile for once daily SR formulation was calculated by the following equation (13) using available pharmacokinetic data (14) Dt= Dose (1+ 0.693 t/t 1/2 where Dt = Total dose of drug Dose= Dose of the immediate release 100
part t= Time during which the sustained release is desired (24 hrs) t 1/2 = Half life of the drug ( 3hrs) The optimum formulation was selected on the above equation so that it could attain complete and controlled drug release upon trading off various response variables; the following maximizing criteria were adopted. rel 2hrs =14.74 rel 8hrs =52.24 rel 12 hrs =82.24 Optimization of Data Analysis and validation of optimization Model Various RSM computations for the current optimization study were performed employing Design Expert Software (Design Expert Version 7.1.3, Stat- Ease Inc, and Minneapolis, MN). Polynomial models including interaction and quadratic terms were generated for all the response variables using multiple linear regression analysis (MLRA) approach. The general form of the MLRA model is represented as the following equation: 2 2 Y= B o + B 1 + B 2 +B 3 + B 4 + B 5 + B 6 2 2 + B 7 Where B 0 is the intercept representing the arithmetic average of all quantitative outcomes of 13 runs. B 1 to B 7 are the coefficients computed from the observed experimental response values of Y: and & are the coded levels of the independent variables. The terms and 2 (i = 1to 2) represent the interaction and quadratic terms respectively. Statistical validity of the polynomials was established on the basis of ANOVA provision in the Design Expert Software. Subsequently, the feasibility and grid searches were performed to locate the composition of optimum formulations (15). Two dimensional (2D) contour plots were constructed based on the model polynomial functions using Design Expert Software. These plots are very useful to see interactions effects on the factors on the responses. Eight optimum checkpoints were selected based on the criteria from optimum formulation described earlier by intensive grid search, performed over the entire experimental domain, to validate the chosen experimental design and polynomial equations. The formulations corresponding to these checkpoints were prepared and evaluated for various response properties. Subsequently, the resultant experimental data of response properties were quantitatively compared with that of their predicted values. Also, linear regression plots between observed and predicted values of the response properties of the Eudragit L 100 and HPMC K 100. were drawn using MS-Excel, forcing the line through origin. RESULTS AND DISCUSSION Drug content and Physical Evaluation The assayed content of drug in various formulations varied between 98.3 ± 0.43 to 99.5 ± 0.3 (mean 98.9 %). Tablet weight varied between 0.250 ± 0.031 to 0.251± 0.032 mg, Thickness between 2.45 to 2.59 mm, Hardness between 6.0-6.3 Kg/ cm2, and friability ranged between 0.079-0.081 percent. Thus all the physical parameters of the matrices were practically within control. In-Vitro drug release studies The In-Vitro dissolution studies ere performed using USP-22 type I dissolution apparatus at 50 rpm and analyzed by UV- visible spectrophotometer. In the current study, the values of release rate exponent (n), calculated as per the Koresmeyer model ranged between 0.6184 and 0.7280 and Zero order release were found to be 0.9867 and 0.9959 (Table - 3) For matrix tablets n value of near 0.5 indicates diffusion control and n value of near 1.0 indicates erosion or relaxation control. Intermediate values suggest that diffusion and erosion contribute to the overall release mechanism. In our experiment the results of n clearly indicated that the diffusion and erosion are the dominant mechanism of drug release from these formulations. Diffusion is related to transport of drug from the dosage matrix into the Invitro study fluid depending on the concentration of the hydrophilic polymer. As gradient varies, the drug is released, and the distance for diffusion increases. This could explain why the drug diffuses at a comparatively slower rate as the distance for diffusion increases. Total amount of Glipizide released from all the formulations up to 8 hrs ranged between 55.24% and 78.46 % indicating in complete drug release at higher concentration of Eudragit L 100 as well as HPMC K 100. Rate of drug release tended to decrease with increase in the content of either Eudragit L 1000 or HPMC K 100. Thereby the viscosity of the gel layer around the tablet increases with increase in the hydro gel concentration, thus limiting the release of active ingredient (16, 17). The gel formed during the penetration of dissolution media into the matrix structure; consist of closely packed swollen particles. With further increase in polymer amount, thicker gel forms inhibiting dissolution media penetration more strongly, resulting in significant reduction in the values of rel 8 hr indicates slower drug release. The values of rel 8hrs enhanced markedly from 55.24-78.46 % and rel 12 hrs from 82.24-98.43, observed at high levels of both the variables. This indicated considerable release retarding potential 101
rel 12 hrs.figure 2 exhibits that rel 2 hrs vary in a non linear to circular fashion, but in a descending pattern with an increase in the amount of HPMC K 15 and Eudragit L 100. In contrast to the results of drug release in 2 hr contour plot for drug release in 8 hrs (Fig 3) reveal that rel 8 hrs varies in somewhat linear with increase in polymers. Fig 4 exhibits an inverted curve, but in an ascending pattern with an increase in the amount of HPMC K 15 and Eudragit L 100. Fig 5 shows the Linear Correlation Plots (A, C, E) between Experimental and Predicted Values and the Corresponding Residual Plots (B, D, F) for various variables. Validation of RSM Results For all of the 8 check point formulations, the results of the physical evaluation and tablet assay were found to be within limits. Table 5 lists the composition of the check points, their predicted and experimental values of all the response variables, and the percentage error in prognosis. Upon comparison of the observed responses with that of the anticipated responses, the prediction error varied between -0.2222 and +0.3287 CONCLUSION Controlled drug release following Koresmeyer Model attained in the current study indicates that the hydrophobic matrix tablet of Glipizide, prepared using HPMC K 15 and Eudragit L 100, can successfully be employed as once a day oral controlled release drug delivery system. Both the polymers play an important role for the sustained release of Glipizide. However, appropriate balancing between various levels of the polymers HPMC K 15 and Eudragit L 100may contribute better results. High degree of prognosis obtained using RSM signifies that a 2 factor CCD is quite efficient in optimizing drug delivery systems. REFERANCES 1. Vidyadhara S, Rao P.R, Prasad J.A, Indian J Pharm Sci; (2004): 66,188-192. 2. Reddy K.R, Mutalik. AAPS Pharm Sci Tech; (2003):4, 1-9. 3. Mohammed A.D, James L.F,Micheal H.R, John E.H, Raabi- Siahboomi A.R, Pharm Dev Tech ; (1999): 4, 313-324. 4. Lee B.J, Ryu S.G, Cui J.H, Drug Dev Ind Pharm, 25, 493-501 (1999) 5. R.K.Varma and S.Garg. Developmental and Evaluation of Osmotic ally controlled oral drug delivery system of Glipizide, Eur J.Pharm.Biopharm57 (2004) 513-525. 6. S. Jamzad and R. Fassihi, Development of Controlled Release Low Dose Class II drug Glipizide Int. J.Pharm,312 (2006) 24-32. 7. Martindale, The complete drug Referance (ed S.C. Sweetman), 34 th ed, Pharmaceutical Press, London 2005, pp 324-348. 8. J.K. Patel, R.P Patel, A.F Amin and M.M Patel, Formulation and Evaluation of Glipizide. 9. K.P.R. Chowdrary and Y.S Rao, Design and Invitro and In vivo Evaluation of Mucoadhesive microcapsules of Glipizide for oral controlled release, AAPS, Pharm sci, Tech 4 (2003). 10. Singh,B, Kumar R, Ahuja N, Crit Rev Ther Drug Carrier Syst 22, 27-105 (2005). 11. Singh B, Mehta G, Kumar R, Bhatia A, Ahuja N, Katare O.P, Curr, Drug Deliv,2, 143-153 (2005). 12. Koresmeyer R W, Gurny R, Doelker E.M Buri P, Peppas N A, Int J Pharm, 15,25 (1983). 13. Rawlins EA Bentleys TextBook of Pharmaceutics, Cassell and Collier Macmillian London, 1977 14. Defang O, Shufang N, Wei L, Drug Dev Ind Pharm, 2005, 31,(677-685). 15. Singh B, Ahuja N, Drug Dev Ind Pharm., 28, 431-442, 2002. 16. Ford JL, Rubinstein MH, Hogan JE, Formulation of Sustained Release Promethazine Hydrocholide Tablets using HPMC matrices Int. J.Pharm 1985,24,327-33/8. 17. Vazques MJ, Perez- Marcos B, Gomez Amoza JL, Martmez- Pachero R, Souto C, Concheiro A. Influence of technological variables on release of drugs from hydrophilic matrices Drug. Dev.Ind. Pharm, 1992:18, 1355-1375. Source of support: Nandha College of Pharmacy, Erode -52, Tamilnadu., Conflict of interest: None Declared 102