Pharmacokinetics of tilmicosin in serum and milk of goats.

Tilmicosin was administered to goats intravenously and subcutaneously to determine its concentration in blood and milk and its kinetic behaviour. After a slow intravenous injection, the serum concentration-time curve indicated a two compartment open model with a mean (SEM) elimination half-life (t1/2 beta S) of 4.36 (0.04) hours. After a subcutaneous injection the drug was eliminated more slowly from serum and milk, with t1/2 beta S of 29.3 and 41.4 hours, respectively. The apparent volume of distribution of tilmicosin was more than 1 litre kg-1. The peak serum tilmicosin concentration was 1.56 micrograms ml-1 6.39 hours after a subcutaneous injection of 10 mg kg-1. Tilmicosin was extensively secreted into milk, reaching a maximum concentration of 11.6 micrograms ml-1 and having a large AUCmilk/AUCserum ratio of approximately 12:1. Tilmicosin was detectable in milk for 11 days after a single subcutaneous dose.