Pharmacokinetics of oral firocoxib in un-weaned calves.
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abstract
The objective of this study was to determine the pharmacokinetics of firocoxib after oral administration in un-weaned calves. Eight Holstein calves with a mean age of 36days and a mean weight of 55kg were administered a single oral dose of 227mg firocoxib. The resulting mean dosage was 4.2mg/kg (range 3.5-5.0mg/kg). Blood was collected prior to drug administration and at 2, 4, 6, 8, 24, 48, 72, and 96h after treatment. Firocoxib concentrations in plasma were determined using liquid chromatography-tandem mass spectrometry. Using computer software, pharmacokinetic parameters were found to fit best with a one-compartment model. Mean Cmax was 0.9g/ml (range 0.570-1.254), and Tmax was estimated to be 7h (range 4-8h). The estimated T1/2 was 15.3h. The pharmacokinetics of firocoxib after oral dosing are similar to those in dogs, with the exception of a T1/2 that is approximately twice as long. Based on the similar pharmacokinetics, it is possible that a dose of 227mg firocoxib orally could provide an analgesic effect in un-weaned calves.