Pharmacokinetics of doxycycline in sheep after intravenous and oral administration

The pharmacokinetics of doxycycline were investigated in sheep after oral (PO) and intravenous (IV) administration. The IV data were best described using a 2- (n = 5) or 3- (n = 6) compartmental open model. Mean pharmacokinetic parameters obtained using a 2-compartmental model included a volume of distribution at steady-state (Vss) of 1.759 ± 0.3149 L/kg, a total clearance (Cl) of 3.045 ± 0.5264 mL/kg/min and an elimination half-life (t1/2β) of 7.027 ± 1.128 h. Comparative values obtained from the 3-compartmental mean values were: Vss of 1.801 ± 0.3429 L/kg, a Cl of 2.634 ± 0.6376 mL/kg/min and a t1/2β of 12.11 ± 2.060 h. Mean residence time (MRT0−∞) was 11.18 ± 3.152 h. After PO administration, the data were best described by a 2-compartment open model. The pharmacokinetic parameter mean values were: maximum plasma concentration (Cmax), 2.130 ± 0.950 μg/mL; time to reach Cmax (tmax), 3.595 ± 3.348 h, and absorption half-life ( t 1 / 2 k 01 ), 36.28 ± 14.57 h. Non-compartmental parameter values were: Cmax, 2.182 ± 0.9117 μg/mL; tmax, 3.432 ± 3.307 h; F, 35.77 ± 10.20%, and mean absorption time (MAT0–∞), 25.55 ± 15.27 h. These results suggest that PO administration of doxycycline could be useful as an antimicrobial drug in sheep.