An HPLC-MS/MS method for simultaneous determination of the active metabolites of febuxostat (67M-1, 67M-2 and 67M-4) in human plasma

An HPLC-MS/MS method for simultaneously determination of the active metabolites (67M-1, 67M-2 and 67M-4) in human plasma using clopidogrel as the internal standard was developed and validated. The compounds were extracted by protein precipitation using acetonitrile and separated using a C8 column by a gradient elution with the mobile phase consisting of acetonitrile (containing 0.1% formic acid) and 0.1% formic acid. Quantification was performed using multiple reaction monitoring in positive mode with m/z transitions of 333.1-261.0, 333.1-261.0, 347.0-261.0 and 322.2-184.1 for 67M-1, 67M-2, 67M-4 and clopidogrel (Internal Standard), respectively. This method was validated in terms of specificity, linearity, precision, accuracy, and stability. The lower limit of quantification of this method was 0.5 ng/mL and the calibration curve was linear over the concentration range of 0.5-150 ng/mL. The intra- and inter-run precision was less than 11.67% and 8.64%, respectively, with the accuracy between 98.33% and 108.38%. The samples were stable under all the tested conditions. This method has been successfully applied to the pharmacokinetic study of febuxostat in healthy Chinese volunteers following oral administration of 40 mg and 80 mg febuxostat.