Determination of ketoconazole in human plasma by high-performance liquid chromatography-tandem mass spectrometry

A simple, rapid and specific high-performance liquid chromatography coupled with tandem mass spectrometry (LC-MS-MS) has been developed and validated for the determination of ketoconazole in human plasma. The method used diethyl ether to extract the ketoconazole and the internal standard (I.S.) R51012 from alkalinized plasma sample. The LC separation was on a C(18) column (50 x 3 mm, 5 microm) using acetonitrile-water-formic acid (75:25:1, v/v/v) mobile phase. The retention times were approximately 1.8 min for both ketoconazole and the I.S. The MS-MS detection was by monitoring 531.2-->82.1 (m/z) for ketoconazole, and 733.5-->460.2 (m/z) for the I.S. The dynamic range was from 20.0 to 10000 ng/ml based on 0.1 ml plasma, with linear correlation coefficient of > or =0.9985. The run time was 2.5 min/injection. The recoveries of ketoconazole and the I.S. were 102 and 106%, respectively. The precision and accuracy of the control samples were with the relative standard deviations (RSDs) of < or =4.4% (n=6) and the relative errors (REs) from -0.6 to 1.4% for intra-day assay, and < or =8.6% RSD (n=18) and -1.4 to 0.9% RE for inter-day assay. The partial volume tests demonstrated good dilution integrity. Three freeze-thaw cycles, keeping plasma samples at ambient for 24 h, storing extracted samples at ambient for 24 h, and storing frozen plasma samples at approximately -20 degrees C for up to 2 months did not show substantial effects.