Evaluation of the Physicochemical and in vitro Dissolution Properties of Metformin Hydrochloride Tablet Brands Marketed in Five Cities in Ghana

Aim: A comparative evaluation of the physicochemical and in vitro dissolution properties of metformin hydrochloride tablet brands sampled in five cities in Ghana was undertaken to assess their pharmaceutical equivalence.

Place and Duration of Study: Department of Pharmaceutics, KNUST, Kumasi, Ghana, between August 2012 and December 2012

Methodology: Fourteen brands of metformin tablets plus the innovator brand, Glucophage, purchased from retail pharmacies were studied. The genuineness of the samples was determined using Fourier transform infra-red (FTIR) spectroscopy and thin layer chromatography (TLC). Pharmacopoeia tests such as uniformity of weight, hardness, friability, disintegration and assay were used to assess the physicochemical equivalence of the tablet brands. In vitro dissolution testing was conducted and the dissolution data subjected to analysis involving dissolution efficiency (DE), similarity factor (f2) and Biopharmaceutics classification system (BCS)-based biowaiver conditions, as a surrogate for bioequivalence studies.

Results: All the tablet brands complied with the official specifications for identification, uniformity of weight hardness and disintegration. Brand M9 failed the friability test while brands M5, M9 and M12 failed the assay test. Dissolution efficiency (DE) and similarity factor (f2) of the brands varied with pH of dissolution media with M4 (in 0.1 M HCl) having the highest DE and M9 (in phosphate buffer pH 6.8) the lowest.

Conclusion: Eleven of the fifteen tablet brands passed all the official tests and could be regarded as pharmaceutically equivalent but f2 analysis showed only six brands were similar to the reference brand (with f2 values ≥50 in the three dissolution media used). None of the metformin brands satisfied the criteria for BCS-based biowaiver for rapidly dissolving tablets. The study has shown that not all the metformin tablet brands sampled in five cities in Ghana are pharmaceutically equivalent.