Objective: To determine the plasma pharmacokinetics and synovial fluid concentrations after oral administration of single and multiple doses of celecoxib in Greyhounds.
Animals: 7 adult Greyhounds.
Procedures: Dogs received celecoxib (median dose, 11.8 mg/kg [range, 11.5 to 13.6 mg/kg], PO, q 24 h) for 10 days. Blood samples were collected prior to administration of celecoxib and serially for 24 hours after the 1st and 10th doses were administered. A synovial joint catheter was placed into a stifle joint in each dog for collection of synovial fluid samples. Concentrations of celecoxib in plasma and synovial fluid were quantified by use of a validated liquid chromatography/mass spectrometry method. Identification of hydroxy- and carboxyl-celecoxib in plasma and synovial fluid was also performed. Pharmacokinetic parameters were determined by use of noncompartmental analysis.
Results: Administration of multiple doses of celecoxib resulted in a significant decrease (40%) in median area under the curve (AUC) values and a corresponding decrease in median maximum concentrations (Cmax; 2,620 to 2,032 ng/mL) between the 1st and 10th doses. Synovial fluid concentrations were less than the corresponding plasma concentrations at all times except 24 hours after administration of the 10th dose of celecoxib.
Conclusions and clinical relevance: Celecoxib distributes into the synovial fluid of Greyhounds. Although the exact mechanism for the decreases in AUC and Cmax is not known, results suggested that the plasma pharmacokinetics of celecoxib are different after administration of multiple doses in Greyhounds. These findings warrant further investigation on the absorption, distribution, metabolism, and elimination of celecoxib in Greyhounds and other breeds of dogs.