Captopril an ACE inhibitor has been used widely for the treatment of hypertension and congestive heart failure. The drug is freely water soluble and has elimination half life after an oral dose of 1.7 to 2 hr. It is stable at pH 1.2 and as the pH increases the drug becomes unstable and undergoes a degradation reaction. Two viscosity grades of Hydroxy propyl methyl cellulose (HPMC4000 and 15000 cps) and carbopol 934p were used to prepare captopril floating capsules. In vitro dissolution was carried out in 0.1 N hydrochloric acid at 37°C ± 0.5°C using USP apparatus method. Compared to conventional tablets, release of captopril from these floating capsules was apparently prolonged; as a result, an 8hr controlled-release dosage form for captopril was achieved. Drug release best fit both the Higuchi model and the Korsmeyer and Peppas model, followed by zero order kinetics. Fitting of the release data to the Korsmeyer and Peppas equation was found that, the drug release rate at 6hr (%) ranges from 29.49 ± 3.58 to 57.34 ± 1.842, the diffusion coefficient (n) ranges from 0.24 ± 0.037 to 0.62 ± 0.069. These results indicated that, the release mechanism is by diffusion. Higuchi release model also indicated that the mechanism of drug release is by diffusion.
