Evaluation of pharmacokinetic properties of vitacoxib in fasted and fed horses.

The pharmacokinetic properties of vitacoxib have not been established completely; current dosage recommendations are based on clinical experiences. The primary objective of this study was to describe plasma concentrations and characterize the pharmacokinetics of vitacoxib formulation following oral administrations in horses. Also, the effect of the state of stomach contents on the absorption of vitacoxib was investigated in fed/fasted horses. Blood samples were collected prior to and at various times up to 72 hr post-administration. Drug concentrations were measured using ultra high-performance liquid chromatography-tandem mass spectrometry. Pharmacokinetic parameters were calculated using Non-Compartmental Analysis Model 200 in WinNonlin (TM) software. No complications resulting from the vitacoxib administration were noted. All procedures were tolerated well by the horses throughout the study. C-max was 17.5 +/- 9.36 ng/ml (fasted) and 9.47 +/- 3.53 ng/ml (fed) following oral administrations. AUC(last) was 173.7 +/- 137.9 ng hr/ml (fasted) and 113.2 +/- 70.8 ng h/ml (fed). No significant differences in pharmacokinetic parameters were noted and the results from the pharmacokinetic analysis were similar between the studies, regardless of precision of dosage and fasted and fed conditions. The study extends previous studies describing the pharmacokinetics of vitacoxib following p.o. administration to the horses. Further studies investigating the pharmacokinetics/pharmacodynamics of vitacoxib are necessary to establish adequate therapeutic protocols (optimal dosage and frequency of administration) in horses.