Simultaneous determination of piroxicam, meloxicam and tenoxicam in human plasma by liquid chromatography with tandem mass spectrometry.

A rapid, sensitive and selective liquid chromatography-tandem mass spectrometric (LC-MS/MS) method for the determination of piroxicam, meloxicam and tenoxicam in human plasma was developed. Piroxicam, meloxicam, tenoxicam and isoxicam (internal standard) were extracted from human plasma with ethyl acetate at acidic pH and analyzed on a Sunfire column with the mobile phase of methanol:ammonium formate (15 mM, pH 3.0) (60:40, v/v). The analytes were detected using a mass spectrometer, equipped with electrospray ion source. The instrument was set in the multiple-reaction-monitoring (MRM) mode. The standard curve was linear (r=1.000) over the concentration range of 0.50-200 ng/ml. The coefficient of variation (CV) and relative error (RE) for intra- and inter-assay statistics at three QC levels were 1.0-5.4% and -5.9 to 2.8%, respectively. The recoveries of piroxicam, meloxicam and tenoxicam ranged from 78.3 to 87.1%, with that of isoxicam being 59.7%. The lower limit of quantification for piroxicam, meloxicam and tenoxicam was 0.50 ng/ml using a 100 microl plasma sample. This method was successfully applied to a pharmacokinetic study of piroxicam after application of transdermal piroxicam patches to humans.