Enhanced plasma availability of moxidectin in fasted horses

The influence of fasting prior to treatment on plasma availability and kinetic disposition of moxidectin was studied in horses. Eight adult crossbred saddle horses were allocated to two experimental groups of four horses. One group was fasted for 24 hours before treatment and the other group received their usual feed. Both groups were treated with an oral gel formulation of moxidectin at the manufacturers recommended therapeutic dose of 0.4 mg/kg. Blood samples were collected by jugular puncture at different times between 0.5 and 50 days. After plasma extraction and derivatization, samples were analyzed by HPLC with fluorescence detection. Computerized pharmacokinetic analyses were done. Fasting induced marked modifications in the pharmacokinetic behavior of moxidectin in the horse. An extended absorption process, and significantly higher area under the curve (AUC) values were obtained in the fasted animals compared to those fed their usual rations. It is suggested that fasting decreases intestinal transit time, and may have prolonged time for absorption of moxidectin. Since, biliary excretion and intestinal secretion are major routes of moxidectin elimination, fasting may have reduced bile flow and intestinal secretion. Fasting before treatment may be a useful tool for improved anthelmintic treatment in horses.