Abstract: AIM: To develop a HPLC-MS method for determining the concentration of lomerizine hydrochloride in human plasma.METHODS: Lomerizine was determined by LC-ESI-MS selection ion measurement.Separation was performed on a Lichrospher C₁₈ with a mobile phase of 0.01mol/L ammonium acetate (pH 3.5):methanol (22:78).RESULTS: Calibration curves were linear in the concentration range of 0.10-10.02 ng/mL (r =0.9993).The quantitative detection limit in plasma was 0.10 ng/mL.RSD of intra-batch and inter-batch assays were all less than 8.59 %.The relative recovery ranged from 100.2 %to 105.9 %and the absolute recovery ranged from 85.58 % to 92.03 %.A single oral dose 10 mg lomerizine hydrochloride capsule or tablet was given to 20 healthy volunteers according to an open randomized crossover study.The concentration of lomerizine hydrochloride in plasma was determined by HPLC-MS method, and the relative bioavailability of AUC_{0 ～ 24} was 103.4 % ±15.6 %.CONCLUSION: This method is rapid, simple, sensitive and accurate for the determination of lomerizine hydrochloride in human plasma.

Key words: lomerizine hydrochloride, HPLC-MS, blood drug level, bioequiavailability