Design and Evaluation of Sustained Release Bilayer Tablets of Oxcarbazepine

Objective The aim of the present study is to modify the release profile of oxcarbazepine by formulating it as a bilayer tablet using direct compression method with dual compression. Methods In the bilayer system, the immediate release layer was formulated using four types of disintegrants, sodium starch glycolate (SSG), croscarmellose sodium (CCS), cross-linked polyvinylpyrrollidone (crospovidone), and starch. It was found that immediate release layer containing sodium starch glycolate gave faster disintegration time. Therefore, sodium starch glycolate was utilized in the preparation of bilayer tablets in this study. The sustained release layer was prepared utilizing three hydrophobic polymers, two of them are acrylics (Eudragit RS (R), Eudragit RL (R)) and the third one is ethyl cellulose. The prepared bilayer tablets were evaluated for hardness, friability, weight variation, content uniformity, and dissolution profile. Results The results showed that combination of Eudragit RL (R) with Eudragit RS (R) in ratio of 2:1 gave the best modified release profile. Also, using di calcium phosphate as a binder and microcrystalline cellulose (Avicel PH 101) as a diluent resulted in a slower release profile comparing with other formulas. Based on the integral 2 similarity factor value comparing with reference standard curve, F15, which contains Eudragit RL (R) and RS (R) in ratio of 2:1 with mannitol as a diluent and Avicel 102 as a binder, was selected as the best optimized formula. Drug release followed diffusion mechanism rather than erosion mechanism. Furthermore, FTIR spectra showed no possibility of chemical interaction between the drug and polymers, which were used in preparation of bilayer tablet. Stability studies of bilayer tablets under accelerated conditions indicated that the shelf life of the prepared tablets was 3 years and 5 months at 25 degrees C. However, stability of optimized formula in day light at room temperature revealed that the shelf life of oxcarbazepine is 1 year and 9 months. Conclusion The results of this study clearly demonstrate that oxcarbazepine can be successfully prepared as a bilayer modified release tablet.