Eprinomectin in dairy goats: dose influence on plasma levels and excretion in milk

The plasma levels and milk excretion of eprinomectin were determined in goats following topical application at doses of 0.5 mg kg(-1) and 1.0 mg kg(-1). The area under the concentration-time curve (AUC) was 2 times lower for 0.5 mg kg(-1) (8.24 +/- 3.50 ng day(-1) ml(-1)) than for 1.0 mg kg(-1) (15.68 +/- 8.84 ng day(-1) ml(-1)), suggesting that the pharmacokinetics of eprinomectin in goats is dose independent. The bioavailability of eprinomectin in lactating compared with non-lactating goats is low. This is probably due to the physiological status of dairy animals, which present a marked decrease in body fat. Comparison of the eprinomectin concentrations in the milk and plasma demonstrated a parallel disposition of the drug with a milk-to-plasma ratio of 0.10-0.25. The amount of drug recovered in the milk was 0.3-0.5% of the total administered dose. In all cases, the maximum level of residue in milk remained below the maximum acceptable level of 30 ng ml(-1) permitted in lactating cattle.