Background: Ectoparasites including ticks, mites, and lice represent a significant source of irritation and dermatologic disease in the horse. Fluralaner, a long-acting ectoparasiticide in the isoxazoline class, is currently used in small animals but the absorption and safety is not well established in horses. Hypothesis/
Objectives: The objective of this study was to describe the pharmacokinetics of fluralaner in horses when administered orally. Animals: Six healthy adult horses from a university teaching herd (3 mares, 3 geldings).
Methods: Fasted horses received a single dose of 10 mg/kg oral fluralaner and were followed for 84 days. Plasma were sampled at 20 predetermined time points. Skin biopsies from the dorsal metacarpal region were collected 1 day after oral administration. Fluralaner concentrations were measured by LC-MS/MS. Neurologic examinations, complete blood counts and serum biochemistries were performed at predetermined time points. Non-compartmental analysis was used to determine pharmacokinetic parameters.
Results: The maximum concentration of fluralaner was 162.1±21.6 ng/ml at 0.42±0.14 days. The terminal half-life was 6.33±4.13 days. Area under the curve was 485.1±151.6 day*ng/ml. Plasma fluralaner was detectable for 21 to 48 days, and in one horse up to 70 days. Skin concentrations were 0.85±0.77 ng/mL at 1 day post administration. No adverse neurologic events were noted throughout the 3 month monitoring period and there were no clinically relevant alterations in blood parameters. Conclusions and clinical importance: Oral fluralaner was well tolerated at 10 mg/kg in healthy adult horses. Plasma half-life in horses is shorter than that reported in dogs at similar doses.
