Design and study of lamivudine oral controlled release tablets

The objective of this study was to design oral controlled release matrix tablets of lamivudine using hydroxypropyl methylcellulose (HPMC) as the retardant polymer and to study the effect of various formulation factors such as polymer proportion, polymer viscosity, and compression force on the in vitro release of drug. In vitro release studies were performed using US Pharmacopeia type 1 apparatus (basket method) in 900 mL of pH 6.8 phosphate buffer at 100 rpm. The release kinetics were analyzed using the zero-order model equation, Higuchi's square-root equation, and the Ritger-Peppas empirical equation. Compatibility of the drug with various excipients was studied. In vitro release studies revealed that the release rate decreased with increase in polymer proportion and viscosity grade. Increase in compression force was found to decrease the rate of drug release. Matrix tablets containing 60% HPMC 4000 cps were found to show good initial release (26% in first hour) and extended the release up to 16 hours. Matrix tablets containing 80% HPMC 4000 cps and 60% HPMC 15,000 cps showed a first-hour release of 22% but extended the release up to 20 hours. Mathematical analysis of the release kinetics indicated that the nature of drug release from the matrix tablets was dependent on drug diffusion and polymer relaxation and therefore followed non-Fickian or anomalous release. No incompatibility was observed between the drug and excipients used in the formulation of matrix tablets. The developed controlled release matrix tablets of lamivudine, with good initial release (20%-25% in first hour) and extension of release up to 16 to 20 hours, can overcome the disadvantages of conventional tablets of lamivudine.