Plasma profile study of moxidectin in a cow and its suckling calf.

The plasma concentration of moxidectin, a macrocyclic lactone endectocide, was investigated in a cow and its suckling calf, using a new chemical assay, following subcutaneous injection (0.2 mg/kg) in the cow. The most striking result was the persistence of moxidectin in the plasma of the cow (mean residence time: 25.66 days). Moxidectin was also detected in the plasma of the calf as a result of the excretion of the drug in the cow's milk and its ingestion by the calf. The cow and calf plasma concentrations and pharmacokinetic parameters showed parallel disposition of the drug. The suckling calf received about 5% of the dose from the cow via the milk.