An improved high performance liquid chromatographic method for determination of cimetidine and its major metabolite in plasma.

An improved HPLC method for the measurement of cimetidine and its major metabolite-cimetidine sulfoxide-is described. The mobile phase was a mixture of methanol-ammonium phosphate (20:80), and methanol was used to elute the drug avoiding the use of acetonitrile, a very hazardous solvent. A device has been developed to wash simultaneously ten or more cartridges and to reduce the time of analysis. With this procedure a plasma sample could be analyzed in less than 30 min. The limit of detection was 0.125 micrograms/ml for cimetidine and 1.00 micrograms/ml for cimetidine sulfoxide. The absolute recovery for cimetidine was 83% and 40% for its major metabolite; is greater than that reported by previous studies. The proposed method is rapid, accurate and precise, and it should be useful for clinical, bioavailability and pharmacokinetic studies of cimetidine.