Metformin is key in the management of type 2 diabetes mellitus but also represents additional financial burden, particularly with the use of branded products. The availability of generic products permits generic substitution with a much-reduced cost of treatment. However, only generic products that offer similar bioavailability with the innovator should be considered. This study was designed to assess the bioequivalence of generic metformin tablets within Nigeria.
Metformin tablets selected from the Nigerian market were appraised for quality following British and United States Pharmacopoeia guidelines. In vivo bioequivalence study in healthy volunteers was applied for a generic and the innovator brand in an open-label, 2-arm, 2-treatment crossover fashion with a 1-week washout period. Blood samples were collected at 0, 0.5, 1, 1.5, 2, 3, 4, 6, 8, 10 and 24 h post-dose. Plasma concentrations of metformin were analysed using a validated high-performance liquid chromatography method, and pharmacokinetic parameters were obtained using the non-compartmental approach. The formulations were considered bioequivalent based on the guidelines by United States Food and Drug Administration, Centre for Drug Evaluation and Research.
Nine generic products met the quality assessment standards, and the in vivo bioequivalence study was carried out in 17 healthy volunteers. The mean values for Cmax, Tmax, AUC0–24, and AUC0–∞ for the innovator brand of metformin were 0.43 ± 0.14 µg/mL, 1.35 ± 0.46 h, 2.03 ± 0.68 µg/mL* h and 2.63 ± 1.11 µg/mL* h respectively; for the generic product, the values were 0.44 ± 0.13 µg/mL, 1.41 ± 0.59 h, 2.04 ± 0.68 µg/mL* h and 2.85 ± 1.37 µg/mL*h. The 90% confidence intervals for the test formulation/reference formulation ratio for Log Cmax, Log AUC0–10 hr and AUC0–∞ were within the bioequivalence limits of 80% to 125% (95.8–106.8, 94.8–105.5 and 96.3–108.4 respectively).
The bioavailability of the test product was not inferior to innovator metformin.
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