Tulathromycin assay validation and tissue residues after single and multiple subcutaneous injections in domestic goats (Capra aegagrus hircus)

Tulathromycin is a macrolide antimicrobial labeled for treatment of bacterial pneumonia in cattle and swine. The purpose of the present research was to evaluate tissue concentrations of tulathromycin in the caprine species. A tandem mass spectrometry regulatory analytical method that detects the common fragment of tulathromycin in cattle and swine was validated with goat tissues. The method was used to study tulathromycin depletion in goat tissues (liver, kidney, muscle, fat, injection site, and lung) over time. In two different studies, six juvenile and 25 market-age goats received a single injection of 2.5mg/kg of tulathromycin subcutaneously; in a third study, 18 juvenile goats were treated with 2.5, 7.5, or 12.5mg/kg tulathromycin weekly with three subcutaneous injections. Mean tulathromycin tissue concentrations were highest at injection site samples in all studies and all doses. Lung tissue concentrations were greatest at day 5 in market-age goats while in the multi-dose animals concentrations demonstrated dose-dependent increases. Concentrations were below limit of quantification in injection site and lung by day 18 and in liver, kidney, muscle, and fat at all time points. This study demonstrated that tissue levels in goats are very similar to those seen in swine and cattle.