Pharmacokinetics of Intravenous and Transdermal Flunixin Meglumine in Wool and Hair Sheep (Ovis aries).

The objective of the study was to evaluate the pharmacokinetics of flunixin meglumine of intravenous (IV) and transdermal (TD) flunixin meglumine administration on different coat types (wool vs. hair) in 12 healthy sheep. Polled dorset (wool) sheep (n = 6) and katahdin (hair) sheep (n = 6) received 2.2 mg/kg IV and 3.3 mg/kg TD with a 10-day washout period between treatments. Plasma samples were obtained for 96 h following both IV and TD administration, respectively. Flunixin concentrations were quantified by use of high-performance liquid chromatography with mass spectrometry, and PK parameters were derived using different modeling techniques. A population non-linear mixed effect model showed that coat type has a significant effect on the absorption rate following TD administration. The mean bioavailability of TD flunixin was not significantly different (48.76% ± 17.49% and 36.61% ± 4.33%; p = 0.093) in wool and hair sheep, respectively. Maximum plasma concentrations following TD administration were higher in wool sheep (1.57 μg/mL; range, 0.6-3.41 μg/mL) compared to hair sheep (0.57 μg/mL; range, 0.36-0.83 μg/mL). The PK results provide further support for clinical studies to examine the efficacy of TD flunixin in different breeds of sheep.