Design and in vitro evaluation of zidovudine oral controlled release tablets prepared using hydroxypropyl methylcellulose.

Oral controlled release matrix tablets of zidovudine were prepared using different proportions and different viscosity grades of hydroxypropyl methylcellulose. The effect of various formulation factors like polymer proportion, polymer viscosity and compression force on the in vitro release of drug were studied. In vitro release studies were carried out using United States Pharmacopeia (USP) type 1 apparatus (basket method) in 900 ml of pH 6.8 phosphate buffer at 100 rpm. The release kinetics were analyzed using Zero-order model equation, Higuchi's square-root equation and Ritger-Peppas' empirical equation. Compatibility of drug with various formulations excipients used 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 10% hydroxypropyl methylcellulose (HPMC) 4000 cps were found to show a good initial drug release of 21% in the first hour and extended the release upto 16 h. Matrix tablets containing 20% HPMC 4000 cps and 10% HPMC 15000 cps showed a first hour release of 18% and extended the release upto 20 h. Mathematical analysis of the release kinetics indicated that the nature of drug release from the matrix tablets 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 zidovudine, with good initial release (17-25% in first hour) and which extend the release upto 16-20 h, can overcome the disadvantages of conventional tablets of zidovudine.