Abstract: AIM: To establish an HPLC-MS-MS method for determination of ritodrine in human plasma and to study the pharmacokinetics for two preparations in health volunteers.METHODS: The plasma was extracted with ethyl acetate. Separation was obtained on BDS Hypersil C₁₈(3 μm,2.1 mm×50 mm)column with the mobile phase of water( 1‰ formic acid)- methanol (20∶80) at the flow rate of 0.20 mL/min. Electrospray ionization source was operated in positive ion mode. Selected reaction monitoring mode with the transitions of m/z 288/270 and m/z 373.4/305.3 were used to quantify ritodrine and the internal standard, respectively.RESULTS: The calibration curve of ritodrine was linear in the range of 0.13-8 ng/mL and detection limit was 0.13 g/L. The intra and inter-day precision (RSD) were less than 12.5% . The absolute recoveries were above 75.4%. To study the pharmacokinetics and the relative bioavailability of two preparations of ritodrine, tablets were given to 18 healthy volunteers. The pharmacokinetics parameters were reported: C_max were (6.1±1.9) and (5.8±2.1) ng/mL;t_max were (1.1±0.4) h and (1.2±0.4) h;t_1/2 were (10±4) h and (9±5) h;AUC_0-36 were (22±9) ng·mL^-1·h and (21±8) ng·mL^-1·h;AUC_0-∞ were (25±10) ng·mL^-1·h and (23±8) ng·mL^-1·h.CONCLUSION: This method is convenient, sensitive, specific and suitable for pharmacokinetics and relative bioavailability study.

Key words: PLC-MS-MS, Ritodrine, Pharmacokinetic, Plasma concentration