Pharmacokinetics of intravenous and intramuscular parecoxib in healthy Beagles

Parecoxib is an inactive pro-drug that is rapidly converted to valdecoxib, a selective cyclooxygenase (COX)-2 inhibitor registered for the management of post-operative pain in humans. Recent studies have suggested that parecoxib has excellent clinical efficacy and safety in veterinary species. The aim of the current study was to assess the pharmacokinetics of parecoxib and valdecoxib after intravenous (IV) and intramuscular (IM) administration. Seven healthy male Beagle dogs received 2.5 mg/kg parecoxib by either the IV or IM route in a cross-over design, with the alternative route of administration used 1 week later. The plasma concentrations of both analytes were detected according to a previously validated method using high performance liquid chromatography with fluorescence detection (HPLC-FL).No adverse effects were observed in any animal during the study. For both routes of administration, parecoxib was rapidly and almost completely converted to valdecoxib. The parecoxib/valdecoxib area under the curve (AUC) ratio for both routes of administration was 1.4. The half-life of valdecoxib was about 2 h, which was shorter than reported for humans, although the plasma concentrations following both routes of administration were likely to be effective for analgesia. The absolute bioavailability of parecoxib was 66%. The pharmacokinetic features of parecoxib make it suitable for treatment of acute pain in the canine species.