Abstract: AIM: To establish an LC-MS method for determining the concentrations of loratadine (LOR)in human plasma and to evaluate its pharmacokinetic characteristics.METHODS: A ZORBAX Eclipse XDB-C8 (5μm , 150 mm ×4.6 mm)column was used , atmospheric pressure electronic spray ionization (AP-ESI) and ion mass spectrum (m/z)of 388.2 (M+H)⁺were selected to quantify LOR , and 275.1 (M +H)⁺for ropivacaine(internal standard , IS).RESULTS: The linear range of LOR standard curve was 0.5 -50 ng·ml^-1 , and the determination limit was 0.5 ng·ml^-1.The pharmacokinetic parameters of LOR after a single dose of 20 mg tablet(T1), capsule (T2)and reference (R)were as follows ,the half life (t_1/2)13.52 ±1.35 , 13.14 ±0.98 and 14.00 ±1.25 h , the time to peak concentration (Tmax) 1.24 ±0.06 , 1.18 ±0.12 and 1.17 ±0.12 h , the peak concentration (Cmax)21.72 ±7.70 , 21.49 ±8.34 and 20.50 ±8.65 ng·ml^-1 , the area under time-concentration curve (AUC_{0 -48} and AUC_{0 -∞})137.24 ±47.84 and 146.61 ±51.03 ng·ml^-1·h , 139.65 ±45.69 and 148.04 ±48.10 ng·ml^-1·h , 134.19 ±49.03 and 143.70 ±52.08 ng·ml^-1·h , the relative bioavailability of LOR tablet and capsule were (105.49 ±8.08)% and(102.90 ±10.02)%, respectively.CONCLUSION: The LC-MS method for determining the concentration of LOR in human plasma is sensitive and accurate and can be used for LOR bioavailability and pharmacokinetic studies.LOR tests and reference are bioequivalent.

Key words: loratadine, LC-MS, pharmacokinetics, bioequivalence, Clarityne