Abstract

The aim of this study was to assess the dissolution properties of twelve sustained release (SR) nifedipine tablet brands, including 20 mg and 30 mg innovator brands, for possible generic substitution. The tablet brands were purchased from retail pharmacies in the Kumasi Metropolis, Ghana. The weight uniformity, drug content and in vitro dissolution of the tablets in phosphate buffer pH 6.8 were evaluated. The dissolution data were compared using the similarity (f2) and difference (f1) factors, and the USP acceptance criteria for SR tablets. The kinetics of drug release from the tablets was also evaluated. All the brands passed the weight uniformity test. Nine brands (75 %) passed the drug content test while three brands (25 %) failed. The two innovator nifedipine SR brands passed all the tests undertaken. Comparison of the dissolution data using f1 and f2 showed that all three 30 mg nifedipine SR brands were dissimilar to the innovator brand. Also, two 20 mg nifedipine SR brands (28.6 %) were similar or bioequivalent with the innovator 20 mg brand while five brands (71. 4 %) were dissimilar. Three (75 %) 30 mg and four (50 %) 20 mg nifedipine SR brands exhibited appropriate drug release profiles based on the USP acceptance criteria. Drug release from the twelve tablet brands mostly followed the Higuchi kinetic model (58.3 %) followed by the Hixson-Crowell model (16.7 %). Only one brand (N7) exhibited constant drug release kinetics. Results from the study have shown that switching or substituting brands of SR nifedipine for patients should be guided by a critical assessment of the dissolution data using appropriate evaluation techniques.

Key words: Nifedipine; sustained release; in vitro dissolution; drug substitution; similarity factor; difference factor