Ketoprofen in horses: Metabolism, pharmacokinetics, and effects on inflammatory biomarkers

Ketoprofen is an anti-inflammatory drug that is commonly administered to racehorses for the alleviation of musculoskeletal pain and inflammation. This study represents a comprehensive examination of the metabolism (in vivo and in vitro), pharmacokinetics and ex vivo pharmacodynamics, of ketoprofen in horses. The in vitro metabolism as well as specific enzymes responsible for metabolism was determined by incubating liver microsomes and recombinant CYP450 and UGT enzymes with ketoprofen. For the in vivo portion, 15 horses were administered a single intravenous dose of 2.2-mg/kg ketoprofen. Blood and urine samples were collected prior to and up to 120 h post-drug administration. Additional blood samples were collected at select time points and were stimulated with calcium ionophore or lipopolysaccharide, ex vivo, to induce eicosanoid production. Drug, metabolite, and eicosanoid concentrations were determined using LC-MS/MS. Incubation of ketoprofen with equine liver microsomes generated 3-hydroxy ketoprofen, an unidentified hydroxylated metabolite, and ketoprofen glucuronide. Recombinant equine CYP2C23 produced the greatest amount of hydroxylated ketoprofen and recombinant equine UGT1A2 generated ketoprofen glucuronide. Dihydro, 3-hydroxy, and glucuronide metabolites were identified in blood and urine samples. The Vd_ss was 0.280, 0.385, and 0.319 L/kg for total ketoprofen, S (+) ketoprofen, and R (-) ketoprofen, respectively. The mean half-life was 6.01 h for total ketoprofen, 2.22 h for S (+) ketoprofen, and 1.72 h for R (-) ketoprofen. Stimulation of ketoprofen-treated blood with lipopolysaccharide and calcium ionophore resulted in an inhibition of TXB₂ , PGE₂ , PGF_2alpha , LTB₄ , and 15(s)-HETE production for up to 120 h post-drug administration.