Bioequivalence assessment of metformin hydrochloride using a limited sampling strategy

The aim of this study was to develop a limited sampling strategy (LSS) that can be used to assess the bioequivalence of two metformin hydrochloride preparations.

Healthy subjects (n = 20) enrolled in the bioequivalence study received a single oral tablet of 1,000 mg metformin reference formulation or test formulation. The plasma concentration of metformin was determined using a validated HPLC method. A multiple linear regression analysis of the observed metformin Cmax and AUC0-24 versus the concentration of reference formulation was performed to develop LSS models for estimating these parameters. The models were internally validated by the Jackknife method. The best models were employed to assess the bioequivalence of the two metformin formulations.

The linear relationship between pharmacokinetic parameters and a single concentration point was poor. Several models for the estimation of these parameters met the predefined criteria (r2 > 0.9). The Jackknife validation procedure revealed that LSS models based on two sampling times - C1.5 and C2 for Cmax; C4.0 and C10.0 for AUC0-24 - were accurate predictor of Cmax and AUC0-24. Prediction errors (PE) were less than 2%, and absolute prediction errors (AE) were less than 10%. PEs beyond 15% occurred in less than 5% of total samples. The bioequivalence assessment of the two metformin formulations, based on the best LSS models, provided results similar to those obtained using all the observed concentration-time data points, and indicated that the two metformin formulations were bioequivalent.

A LSS method for assessing the bioequivalence of metformin formulations was established and proved to be applicable and accurate. This LSS method could be considered appropriate for a metformin bioequivalence study, providing an inexpensive cost of sampling acquisition and analysis.