Ivermectin in goat plasma and milk after subcutaneous injection.

The pharmacokinetics and mammary excretion of ivermectin were determined in goats following a single sc administration (0.2 mg/kg). Kinetic analysis of plasma and milk levels was performed using a 1-compartment model. The maximum plasma concentration of 6.12 ng/ml occurred at 2.85 d; the half-life of 4.03 d was similar to the value in sheep (3.68 d). Ivermectin was detected in the milk at the first sampling time and thereafter for at least 25 d. Comparison of the milk and plasma data shows the parallel disposition of the drug in milk and plasma with a milk-plasma concentration ratio of 1.08 +/- 0.23. In conclusion, the persistence of the drug in plasma is reflected in the duration of the presence of ivermectin in milk.