HPLC-MS/MS Method for the Quantitative Determination of Metformin in Rat Plasma and Its Application to Comparative Bioavailability Assessment

Background:: Metformin is a biguanide derivative utilized as a first-line treatment for type 2 diabetes for people over 60 years. However, it faces certain limitations due to its incomplete absorption, resulting in a 50-60% bioavailability. In addition to its blood glucose-lowering effect, the antiproliferative effect of metformin has been demonstrated in vitro. Therefore, it is necessary to consider alternative administration routes that can enhance the bioavailability of metformin, expanding its clinical use beyond its role as an antidiabetic agent. Objective:: The aim of the study was to develop a reliable bioanalytical method for the quantitation of metformin in male Sprague-Dawley rat plasma and explore the promising alternative administration route for metformin use. Methods:: A robust, high-performance liquid chromatography-tandem mass spectrometry method for the quantification of metformin in rat plasma was developed and validated according to the latest regulatory guidance for bioanalysis. Results:: Based on the area under the curves obtained from the rat pharmacokinetic study, subcutaneous injection increased the systemic exposure of metformin by 1.79-fold compared to oral administration in rats. Conclusion:: Subcutaneous administration of metformin enhances its bioavailability compared to oral administration, leading to increased antidiabetic effects and potential antitumor activity.