Pharmacokinetics of firocoxib in preweaned calves after oral and intravenous administration.

The objective of this study was to determine the pharmacokinetics of intravenous and oral firocoxib in 10 healthy preweaned calves. Firocoxib (0.5 mg/kg) was initially administered i.v. to calves, and following a 14-day washout period, animals received firocoxib orally prior to cautery dehorning. Firocoxib concentrations were determined by liquid chromatography-tandem mass spectrometry. Changes in hematology and plasma chemistry were determined using automated methods. Computer software was used to estimate pharmacokinetic parameters best described with a two-compartment model for i.v. administration and a one-compartment model for p.o. administration. Following i.v. dosing, the geometric mean (range) T1/2K10 and T1/2β were 6.7 (4.6-9.7) and 37.2 (23.5-160.4) h, respectively, Vss was 3.10 (2.10-7.22) L/kg, and CL was 121.7 (100.1-156.7) mL/h/kg. Following oral administration, geometric mean (range) Cmax was 127.9 (102.5-151.3) ng/mL, Tmax was 4.0 (2.6-5.6) h, and T1/2K10 was 18.8 (14.2-25.5) h. Bioavailability of oral firocoxib was calculated using the AUC derived from both study populations to be 98.4% (83.1-117.6%). No adverse clinical effects were evident following firocoxib administration. Pharmacokinetic analysis of i.v. and p.o. firocoxib indicates high bioavailability and a prolonged terminal half-life in preweaned calves.