Pharmacokinetics of oxytetracycline and tulathromycin in plasma and semen of beef bulls

Abstract

Objectives were to evaluate the pharmacokinetic parameters of tulathromycin and long-acting oxytetracycline in bulls’ plasma and
semen. In the first experiment, long-acting oxytetracycline (10 or 20 mg/kg) were given to bulls either subcutaneously or intramuscularly.
In the second experiment, tulathromycin (2.5 mg/kg) was given subcutaneously. Liquid chromatography coupled with tandem mass
spectrometry was used to measure antibiotic concentrations in plasma and semen samples. Plasma maximum concentration (Cmax) for
10 mg/kg oxytetracycline was 2,841 ng/ml at 12 hours (Tmax) with a half-life of 20.1 ± 5.9 hours. Semen Cmax was 11,515 ng/ml at 24
hours (Tmax) with a half-life of 23.7 ± 4.1 hours. For 20 mg/kg, the plasma Cmax was 5,269 ng/ml at 12 hours (Tmax) with a half-life of 18.1
± 0.4 hours. Semen Cmax was 55,040 ng/ml at 24 hours (Tmax) with a half-life of 15.7 ± 1.2 hours. Plasma Cmax of tulathromycin was 160
ng/ml at 21 ± 6 hours (Tmax). Semen Cmax was 1,539 ng/ml at 33.0 ± 18.0 hours (Tmax). The Cmax between plasma and semen was different
(p = 0.008). Plasma terminal half-life (81.4 ± 27.6 hours) of tulathromycin had a tendency (p = 0.10) to be shorter than semen (114.7
± 21.7). It was concluded that for genital infections of bulls either tulathromycin or long-acting oxytetracycline are adequate antibiotics
based on their pharmacokinetic properties.