Background Sustained-release dosage forms provide an immediate dose required for the therapeutic response followed by the gradual release of drug in amounts sufficient to maintain the therapeutic response for a specific extended period of time.

Zidovudine (AZT) was the first anti-HIV compound approved for clinical use. After oral administration it’s rapidly adsorbed from the gastrointestinal tract and the biological half-life is 4 h, necessitating frequent administrations to maintain constant therapeutic drug levels.

Purpose To formulate an extended-release tablet of AZT using hydrophilic polymers (Eudragit) and hydrophobic ethylcellulose.

Materials and methods AZT, Eudragit and hydrophobic ethylcellulose were provided from Sigma. All chemicals and reagents used were of analytical grade. The in vitro dissolution measurements were performed using Italian Pharmacopoeia dissolution apparatus. The dissolution medium consisted of 0.1N hydrochloric acid for 2 h and phosphate buffer (pH 7.4) for 3 to 10 h, maintained at 37°C ± 0.5°C. Spectrophotometer measurements were performed at 266 nm with a Perkin Elmer Lambda 45 UV-vis spectrophotometer in a Helma 10 mm quartz cell. Tablets were prepared granulating 500 mg of AZT with polymers. Data was subjected to ANOVA followed by t-test using ‘Statistica’ software. A confidence limit of p <0.05 was fixed for interpretation of the results.

Results The drug release was slower from tablets containing Eudragit than that from conventional tablets. Drug release decreased significantly when 30% of Eudragit was used in tablet formulation. Further increase in concentration didn’t affect the release rate. The conventional formulation showed complete dissolution in one hour, tablets containing Eudragit in about six hours, batches containing Eudragit and ethylcellulose in 12 h.

Conclusions Results demonstrated that combination of Eudragit and ethylcellulose could be successfully employed for formulating sustained-release tablets. This can reduce the frequency of administration and decrease dose-dependent side effects associated with repeated administration of conventional tablets.

No conflict of interest.