Pharmacokinetics of flunixin meglumine in donkeys, mules, and horses

Abstract

Objective - To compare serum disposition of flunixin meglumine after IV administration of a bolus to horses, donkeys, and mules. Animals - 3 clinically normal horses, 5 clinically normal donkeys, and 5 clinically normal mules. Procedure - Blood samples were collected at time zero (before) and 5, 10, 15, 30, and 45 minutes, and at 1, 1.25, 1.5, 1.75, 2, 2.5, 2.75, 3, 3.5, 4, 4.5, 5, 5.5, 6, and 8 hours after IV administration of a bolus of flunixin meglumine (1.1 mg/kg of body weight). Serum was analyzed in duplicate by the use of high-performance liquid chromatography for determination of flunixin meglumine concentrations. The serum concentration- time curve for each horse, donkey, and mule were analyzed separately to estimate noncompartmental pharmacokinetic variables. Results - Mean (± SD) area under the curve for donkeys (646 ± 148 minute · μg/ml) was significantly less than for horses (976 ± 168 minute · μg/ml) or for mules (860 ± 343 minute · μg/ml). Mean residence time for donkeys (54.6 ± 7 minutes) was significantly less than for horses (110 ± 24 minutes) or for mules (93 ± 30 minutes). Mean total body clearance for donkeys (1.78 ± 0.5 ml/kg/h) was significantly different from that for horses (1.14 ± 0.18 ml/kg/h) but not from that for mules (1.4 ± 0.5 ml/kg/h). Significant differences were not found between horses and mules for any pharmacokinetic variable. Conclusion and Clinical Relevance - Significant differences exist with regard to serum disposition of flunixin meglumine in donkeys, compared with that for horses and mules. Consequently, flunixin meglumine dosing regimens used in horses may be inappropriate for use in donkeys.