Determination of parecoxib and valdecoxib in rat plasma by UPLC-MS/MS and its application to pharmacokinetics studies.

BACKGROUND: The present study aimed to develop and validate a rapid, selective, and reproducible ultra-performance liquid chromatography-tandem mass spectrometry separation method for the simultaneous determination of the levels of parecoxib and its main metabolite valdecoxib in rat plasma. Moreover, this method was applied to investigate the pharmacokinetics of parecoxib and valdecoxib in rats. METHODS: Following the addition of celecoxib as an internal standard, one-step protein precipitation by acetonitrile was used for sample preparation. The effective chromatographic separation was carried out using an ACQUITY UPLC(R)BEH C18 reversed phase column (2.1 mm x 50 mm, 1.7 mum particle size) with acetonitrile and water (containing 0.1% formic acid) as the mobile phase. The procedure was performed in less than 3 min with a gradient elution pumped at a flow rate of 0.4 ml/min. The electrospray ionization source was applied and operated in the positive ion mode and multiple reaction monitoring mode was used for quantification using the following: target fragment ions: m/z 371 --> 234 for parecoxib, m/z 315 --> 132 for valdecoxib and m/z 382 --> 362 for celecoxib. RESULTS: The method validation demonstrated optimal linearity over the range of 50-10,000 ng/ml (r(2) >/= 0.9996) and 2.5-500 ng/ml (r(2) >/= 0.9991) for parecoxib and valdecoxib in rat plasma, respectively. CONCLUSIONS: The present study demonstrated a simple, sensitive and applicable method for the quantification of parecoxib and its main pharmacologically active metabolite valdecoxib following sublingual vein administration of 5 mg/kg parecoxib in rats.