The Release Behavior and Kinetic Evaluation of Diltiazem HCl from Various Hydrophilic and Plastic Based Matrices

In this study, the effects of various hydrophilic (HPMC and Carbopol 971) and plastic (Ethylcellulose and Eudragit RL100) polymers on the release profile of diltiazem HCl from matrix tablets were evaluated in-vitro. For this purpose, tablets containing 60 mg of diltiazem HCl along with various amounts of the aforementioned polymers were prepared using the wet granulation technique. Tablets prepared were placed in a USP apparatus I dissolution tester containing a pH-1.5 HCl solution for the first 2 h and a pH-6.8 phosphate buffer for the next 10 h of the study. The amount of drug released was determined at 237 nm by a UV-visible spectrophotometer. The results showed that all the polymers used in this study could slow down the release of diltiazem HCl from the matrices prepared. This effect, except for HPMC, generally increased proportionately with the amount of polymer. HPMC imparted the best control over drug release and could sustain it for approximately 6 h. All the matrices prepared had a burst release initially; however, it was minimum with HPMC-containing formulations. Fitting of release data to different kinetic models showed that HPMC-matrices conformed best to Hixson-Crowell model, ethylcellulose-matrices to Higuchi and both Eudragit RL100 and Carbopol 971-formulations to either of Hixson-Crowell, Higuchi and first-order kinetics. Release exponent (n) derived from Korsmeyer-Peppas equation for the studied formulations implied that the release of diltiazem HCl from HPMC-matrices was non-Fickian (0.62-0.66) and that of ethylcellulose-formulations was Fickian (n~0.4). The values of n for Eudragit RL100 and Carbopol 971-matrices ranged from 0.46-0.59, indicating that the drug release was mainly governed by diffusion. Briefly, HPMC was found to be suitable for sustaining the release of diltiazem HCl from matrix-type tablets. Nevertheless, to achieve better results with this polymer, further investigations seem to be necessary.