Pharmacokinetics, metabolism and excretion of celecoxib, a selective cyclooxygenase-2 inhibitor, in horses

Celecoxib, a nonsteroidal anti-inflammatory drug, is frequently used to treat arthritis in humans with minimal gastrointestinal side effect compared to traditional NSAIDs. The primary aim of this study was to determine the pharmacokinetic profile of celecoxib-a selective cyclooxygenase-2 (COX-2) inhibitor in horses. Six horses were administered a single oral dose of celecoxib at 2 mg/kg (body weight). After oral dosing, the drug reached a maximum concentration (mean +/- SD) in blood of 1,088 +/- 324 ng/ml in 4.58 hr. The elimination half-life was 13.60 +/- 3.18 hr, and the area under the curve was 24,142 +/- 1,096 ng hr ml(-1). The metabolism of celecoxib in horses was via a single oxidative pathway in which the methyl group of celecoxib is oxidized to a hydroxymethyl metabolite and is further oxidized to form a carboxylic acid metabolite. Celecoxib is eliminated mainly through faeces as unchanged drug and as metabolites in urine. Therefore, instructions for a detection time following therapeutic dosing of celecoxib can be set by the racing practitioner and veterinarians to control illegal use in horse racing based on the results of this study.