Determination of vitacoxib, a novel COX-2 inhibitor, in equine plasma using UPLC-MS/MS detection: Development and validation of new methodology.

Vitacoxib is an imidazole derivative and the novel COX-2 selective inhibitor to be marketed for veterinary use as nonsteroidal anti-inflammatory drugs. No analytical assay to quantify vitacoxib in equine plasma samples has been published to date. In the current study, we aim to develop and validate a brief, quick and sensitive UPLC-MS/MS method for quantification of vitacoxib in equine plasma samples. Plasma samples were precipitated with methyl tert-butyl ether. The Phenomenex column (Kinetex 50×2.1mm i.d. particle size=2.6μm, C18, 100Å) at 25°C was used in chromatographic separation with mobile phase consisting of acetonitrile and water (containing 0.1% formic acid) at flow rate of 0.4mL/min. Vitacoxib and internal standard (IS, celecoxib) were detected under the multiple-reaction monitoring mode by mass spectrometer with ESI+ (m/z 347.9/269.03 for vitacoxib and m/z 382.0/362.0 for IS, respectively). The curve concentration range of was 0.5-500ng/mL with a lower limit of quantification 0.5ng/mL (r2=0.996309) in equine plasma samples. The selectivity, precision, recovery, accuracy, matrix effect and stability under various conditions were conformed to the acceptance requirements. Pharmacokinetic studies of vitacoxib in horses via oral administration (0.1mg/kg) demonstrated that the procedure was fully validated and successfully. A meaningful basis for assessing the vitacoxib or clinical applications of vitacoxib to horse is provided in the present study.