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 concentr ations of flunixin were measured by high performance liquid chromatogr aphy. The decline in plasma, flunixin concentration with time was best fitted by a triexponential equation. The pharmacokinetics following i ntravenous administration of 1.0 mg/kg indicate that flunixin has a ra pid distribution half-life (t1/2pi = 2.3 min), a slow body clearance r ate (Cl(b) = 0.6 ml/kg/min) and an elimination half-life of 229 min. S imilarly, at 2.0 mg/kg, flunixin is rapidly distributed from the plasm a, t1/2pi = 2.7 min, has a slow body clearance rate (Cl(b) = 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 si te. It had a mean maximum concentration (C(max)) of greater-than-or-eq ual-to 5.9 mug/ml when administered at a dose rate of 1.1 mg/kg, and a relative bioavailability of 70%. Plasma concentrations increase propo rtionally to dose over the range 1.1 mg/kg-2.2 mg/kg when administered by the intramuscular route.