Pharmacokinetics of flunixin meglumine in mature swine after intravenous, intramuscular and oral administration

BACKGROUND The purpose of this study was to determine intravenous (IV), intramuscular (IM) and oral (PO) FM PK in mature swine. Appropriate pain management for lameness in swine is a critical control point for veterinarians and producers, but science-based guidance on optimal housing, management and treatment of lameness is deficient. Six mature swine (121-168 kg) were administered an IV, IM, or PO dose of flunixin meglumine at a target dose of 2.2 mg/kg in a cross-over design with a 10 day washout period between treatments. Plasma samples collected up to 48 hours post-administration were analyzed by high pressure liquid chromatography and mass spectrometry (HPLC-MS) followed by non-compartmental pharmacokinetic analysis. RESULTS No adverse effects were observed with flunixin meglumine administration for all routes. Flunixin meglumine was administered at an actual mean dose of 2.21 mg/kg (range: 2.05-2.48 mg/kg) IV, IM and PO. A mean peak plasma concentration (CMAX) for IM and PO administration was 3748 ng/ml (range: 2749-6004 ng/ml) and 946 ng/ml (range: 554-1593 ng/ml), respectively. TMAX was recorded at 1.00 hour (range: 0.50-2.00 hours) and 0.61 hours (range: 0.17-2.00 hours) after PO and IM administration. Half-life (T ½ λz) for IV, IM and PO administration was 6.29 hours (range: 4.84-8.34 hours), 7.49 hours (range: 5.55-12.98 hours) and 7.08 hours (range: 5.29-9.15 hours) respectively. In comparison, bioavailability (F) for PO administration was 22% (range: 11-44%) compared to IM F at 76% (range: 54-92%). CONCLUSIONS The results of the present study suggest that FM oral administration is not the most effective administration route for mature swine when compared to IV and IM. Lower F and Cmax of PO-FM in comparison to IM-FM suggest that PO-FM is less likely to be an effective therapeutic administration route.