The comparative evaluation of the physicochemical properties and in vitro dissolution of some expired and unexpired brands of metformin tablets, six brands of expired (serial 1)and also unexpired (serial 2) of the same brand were used. The samples were determined using thin layer chromatography (TLC). Pharmacopoeia tests such as uniformity of weight, hardness, friability and assay were used to assess the physicochemical equivalence of the expired and unexpired metformin tablet brands. In vitro dissolution testing was conducted for both the expired and the unexpired tablets. All the brands (expired-serial 1) and (unexpired-serial 2) conformed to the British pharmacopoeia standard. All brands complied except C1 and F1 (within the range of not more than 1% (BP 2013) therefore brand C1 and F1 failed the friability test, the unexpired brand has higher crushing strength than the expired brands. Also for the assay content the unexpired brands has higher percentage content than the expired. The Dissolution test carried out, all the unexpired brands met the 70% drug released in 45 min (BP 2013) specification. The expired brands A1, D1, E1, F1 has lower percentage of drug released at 45 min, the unexpired brands has higher percentage of drug released at 45min compared to the unexpired. The thin layer chromatography (TLC) shows higher Rf value for the expired and there was an additional spot for the expired brands as compared to the unexpired brands.
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