Pharmacokinetics of diclofenac in sheep following intravenous and intramuscular administration

The aim of this work was to examine the pharmacokinetics of diclofenac (DCLF) in sheep after intravenous (IV) and intramuscular (IM) dosing. Healthy male Najdi sheep. Diclofenac (1 mg kg−1) was administered to ten clinically healthy-male Najdi sheep IV or IM (n = 5 each). Blood samples (5 mL) were collected and serum was separated for drug analysis by high-performance liquid chromatography with UV detection. Diclofenac pharmacokinetic parameters were determined by noncompartmental analysis. Diclofenac is quickly eliminated from sheep with a terminal T1/2λ of 2–3 hours for both routes of administration. Total DCLF clearance after IV and IM administration was 87.86 ± 24.10 and 85.69 ± 40.76 mL kg−1 hour−1 respectively. The absolute bioavailability of IM DCLF appears to be approximately 100%. The drug should be administered two to three times daily in sheep by IM or IV injection to maintain therapeutic concentrations. Additional studies are needed to evaluate the route of elimination of DCLF in sheep including metabolites formation and the significance of enterohepatic circulation.