Colon Targeted Press Coated Tablets of Venlafaxine Hydrochloride for Treatment of Depression

Objective: The aim of this study was to develop a colon targeted press coated tablet of venlafaxine hydrochloride (VH) for the chronotherapy of depression. The press coating technique for colon targeting can overcome the limitations associated with the solvent coating technique. Methodology: The core tablets were prepared by direct compression using different ratios of VH:HPMC K100M (1:1, 1:2, 1:3). Core tablets were evaluated for various parameters such as average weight, thickness, hardness, friability, swelling index and in vitro drug release. A coating layer of guar gum and ethylcellulose in different ratio (1:0.25, 1:0.5, 1:1, 0.5:1, 0.25:1) was applied on the core tablet by press coating technique. Press coated tablets were evaluated for various parameters such as average weight, thickness, hardness, friability and in vitro drug release. Results: The drug release from the core tablets decreased with increased amount of HPMC K100M. F3 was selected as an optimized formulation for core tablets due to sustained drug release upto 3 hours. The drug release from optimized formulation followed Higuchi matrix kinetics and mechanism of release was found to be Fickian diffusion. The coating layer was soft and friable with formulation containing a higher proportion of guar gum as compared to ethylcellulose. The in vitro release from optimized press coated tablet PC3 followed the first order kinetics. Conclusion: The formulation (PC3) coated with granules containing guar gum and ethylcellulose (1:1) showed the desired average lag time of 5 h for the chronotherapy of depression by colon targeting.