Incurred sample stability of metformin hydrochloride in plasma of six healthy subjects using high-performance liquid chromatography

Objective: This study aimed to measure metformin levels and evaluates the incurred stability in plasma of six healthy subjects after administration 850 mg metformin hydrochloride tablet using high-performance liquid chromatography. Methods: Samples were collected from six healthy subjects who were administered 850 mg metformin hydrochloride tablet. Blood was collected from the subjects at up to 12-time points throughout a 12 h period. Sample stability was analyzed on days 7, 14, and 30. The analysis was conducted using C-18 columns, a column temperature of 40°C, a mobile phase consisting of acetonitrile-phosphate buffer (pH 7.0; 40:60 v/v), a flow rate of 1 mL/min, the photodiode array detector set at a wavelength of 234 nm, and calcium atorvastatin as the internal standard. Results: All metformin HCl samples collected on days 7, 14, and 30 from subjects 1 to 6 met stability requirement based on the European Medicines Agency Bioanalytical Guideline (2011), which state that the percentage difference value not >20%. In addition, the developed method for analyzing metformin HCl in plasma was linear in the concentration range of 20.0-5000.0 ng/mL (r=0.9999). Conclusion: The incurred sample of metformin hydrochloride in plasma of six healthy subjects was stable until 30 days after drug administration.