Simultaneous determination of metformin, captopril, lisinopril, and enalapril by RP-HPLC: its applications in dosage formulations and in human serum

A simple, rapid, isocratic, high-performance liquid chromatography (HPLC) method has been developed for the first time for simultaneous determination of Metformin and ACE inhibitors (lisinopril, captopril, enalapril, and its degradable product) in bulk drugs, pharmaceutical products and in human serum. The separation was performed on a Purospher(A (R)) Star RP-18 endcapped (250 mm x 4.6 mm id) column using methanol-water as mobile phase 50:50 (v/v) and 60:40 (v/v) as diluent. The pH of mobile phase was adjusted to 3.2 with ortho-phosphoric acid, flow rate was adjusted to 1 mLmin(-1) at room temperature (25 A degrees C) and analytes peaks were observed using UV detector at 218 nm. The retention times and LOD of lisinopril, enalapril, enalapril diketopiperazine, and captopril were 2.24, 2.63, 3.82, 4.28, and 4.78 min and were 0.028, 0.044, 0.20, 0.016, and 0.145 mu gmL(-1) respectively. The method was validated according to ICH guidelines. The linearity of the method was studied over the concentration range of 5-50 mu gmL(-1) for metformin and 2.5-250 mu gmL(-1) for the ACE inhibitors, where it demonstrated good linearity with r = 0.9998, 0.9979, 0.9997, and 0.9987 (n = 6), respectively. The developed method was successfully applied to quantitate metformin, lisinopril, captopril, and enalapril in pharmaceutical formulations and human serum.