The pharmacokinetics of flunixin meglumine in the sheep

Flunixin meglumine was administered intravenously and intramuscularly in sheep and the pharmacokinetics of the drug studied. Plasma concentrations of flunixin were measured by high performance liquid chromatography. The decline in plasma flunixin concentration with time was best fitted by a triexponential equation. The pharmacokinetics following intravenous administration of 1.0 mg/kg indicate that flunixin has a rapid distribution half-life (t1/2 pi = 2.3 min), a slow body clearance rate (Clb = 0.6 ml/kg/min) and an elimination half-life of 229 min. Similarly, at 2.0 mg/kg, flunixin is rapidly distributed from the plasma, t1/2 pi = 2.7 min, has a slow body clearance rate (Clb = 0.7 ml/kg/min) and an elimination half-life of 205 min. Following intramuscular injection flunixin is rapidly and well absorbed from the injection site. It had a mean maximum concentration (Cmax) of > or = 5.9 micrograms/ml when administered at a dose rate of 1.1 mg/kg, and a relative bioavailability of 70%. Plasma concentrations increase proportionally to dose over the range 1.1 mg/kg-2.2 mg/kg when administered by the intramuscular route.