Pharmacokinetics of rafoxanide in suckling and weaned lambs following oral administration.

The pharmacokinetics of rafoxanide administered orally at 15 mg kg-1 were compared in suckling lambs (n = 8), aged 5-8 weeks and weaned lambs (n = 8), aged 21-22 weeks. A significant difference (p < 0.0001) in area under the curve (AUC) and maximum plasma concentrations (Cmax) were observed between the different age groups. The bioavailability, as measured by AUC and Cmax, was 2.5-3 times greater in the suckling lambs compared to the weaned lambs. No significant differences (p > 0.05) in time to maximum plasma concentrations (Tmax), distribution half-life (T1/2 alpha), elimination half-life (T1/2 beta) and mean residence time (MRT) were observed. It was concluded that the pharmacokinetic differences observed between suckling and weaned lambs may result in an increased susceptibility of suckling lambs to the toxic effects of rafoxanide. Lambs younger than 8 weeks, should preferably not be treated with rafoxanide, or the dose must be reduced.