Pharmacokinetics of tulathromycin in nonpregnant adult ewes.

The objectives of this study were to determine plasma concentrations and pharmacokinetic parameters of tulathromycin after a single subcutaneous administration in the cervical region in sheep using the cattle labeled dose of 2.5 mg/kg. Six adult healthy ewes were administered tulathromycin on day 0. Blood samples were collected just prior to dosing and at selected time points for 360 h. Plasma samples were analyzed to determine tulathromycin concentrations, and noncompartmental analysis was performed for pharmacokinetic parameters. The mean maximum plasma concentration was 3598 ng/mL, the mean time to maximum concentration was 1.6 h, and the apparent elimination half-life ranged from 68.1 to 233.1 h (mean 118 h). When comparing our results to goats and cattle, it appears sheep are more similar to cattle in regard to the concentrations observed and pharmacokinetic parameters. In summary, the pharmacokinetics of tulathromycin in sheep appear to be similar enough to those in goats and cattle to recommend similar dosing (2.5 mg/kg SC), assuming that the target pathogens have similar inhibitory concentrations.