Abstract: AIM: To determine the concentration of escitalopram in human plasma by HPLC-MS MS and investigate the pharmacokinetics of escitalopram.METHODS: The method involved protein precipitation with methanol.The chromatographic separation was achieved within 6.0 min by using methanol-water with 15 mmol·L^-1ammonium acetate-formic acid (72 ∶28 ∶0.1, v/v/v) as mobile phase and a Lichrospher CN 150 mm ×4.6 mm analytical column.The analytes were detected using an electrospray ionization tandem mass spectrometry in SRM mode.Detection of the ions was performed by monitoring the transitions of m/z 325.0 to 234.0 for escitalopram and m/z 409.1 to 238.1 for amlodipine(internal standard) , respectively.RESULTS: The standard curve was linear (r =0.999) over the concentration range of 0.20 -50.00 ng·ml^-1.Accuracy and precision were below the acceptance limits of 15%.The recoveries of escitalopram ranged from 96.0% to 103.6%.The lower limit of quantification for escitalopram was 0.20 ng·ml^-1 using 200 μl plasma sample.The pharmacokinetic parameters of escitalopram after a single oral dosing of escitalopram oxalate tablet (10 mg)to ten healthy male volunteers were achieved.The C_max ,T_max , AUC_{0 -t} , AUC_{0 -∞}, t_{1 2}and K e of escitalopram were 9.21 ±2.10 ng·ml^-1 , 3.75 ±1.04 h, 514.6 ±152.3 ng·h·ml^-1 , 540.5 ±162.3 ng·h·ml^-1 , 34.06 ±7.71 h and 0.021 ±0.004 h^-1 , respectively.CONCLUSION: The determination of concentration of escitalopram in human plasma by HPLC-MS MS method was rapid, sensitive and reliable.It can be used for clinical pharmacokinetic study of escitalopram.

Key words: escitalopram, HPLC-MS/MS, human plasma, pharmacokinetics