Abstract
Objective: The objective of this work was to evaluate the in vitro release performance of metformin hydrochloride formulations (500-mg tablets) using the hydrodynamic environment of the flow-through cell method. Results were compared with those generated by the official dissolution test (USP basket apparatus).
 Methods: The reference drug product and three generic formulations were tested with phosphate buffer pH 6.8 as dissolution medium. Dissolution profiles were carried out with an automated flow-through cell apparatus using laminar flow at 16 ml/min. Drug was quantified at 233 nm during 45 min. Dissolution profiles were compared with the calculation of f2 similarity factor, mean dissolution time, dissolution efficiency, t50% and t63.2%. Dissolution data were adjusted to several mathematical models such as Makoid-Banakar, Peppas-Sahlin, Weibull and Logistic.
 Results: With the flow-through cell method and at 45 min less than 60% of metformin hydrochloride dissolved was found, while with the USP basket apparatus, less than 75% of the drug was found. Some generic formulations showed f2>50 with both USP apparatuses, but statistical comparisons of parameters indicated significant differences between their dissolution profiles and reference. Due to variability obtained no dissolution profiles were compared by model-dependent approach.
 Conclusion: To demonstrate safe interchangeability between metformin hydrochloride generic formulations and reference bioequivalence studies should be performed. It is important post-marketing monitoring of the commercial formulations because health regulatory agencies of each country must ensure drug products with quality, safety, and efficacy at the lowest possible cost.
Highlights
Generics are off-patent formulations that contain the same active pharmaceutical ingredient, and the same dose, as reference drug product [1]
Metformin hydrochloride is manufactured as generic drug products and by the results reported by other authors there is a need to evaluate generics even after going on sale with the aim of offering the population safe and quality medicines
Results of content uniformity and assay tests made to metformin hydrochloride formulations are shown in table 2
Summary
Generics are off-patent formulations that contain the same active pharmaceutical ingredient, and the same dose, as reference drug product [1]. Many generic formulations have shown significant differences from their branded counterparts. Metformin is a member of the biguanide class of drugs and is used in the treatment of type 2 diabetes mellitus [2]. This type of diabetes is characterized by abnormally high levels of glucose in the blood due to either insulin resistance of the cells or too much glucose production in the liver or a combination of both situations [3]. Molecular structure of metformin hydrochloride is shown in fig. Molecular structure of metformin hydrochloride is shown in fig. 1
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