Comparative pharmacokinetics of difloxacin in goat kids and lambs

The purpose of this study was to investigate the comparative pharmacokinetics of difloxacin in male goat kids and lambs. Difloxacin was administered in a crossover as a single dose of 5 mg kg−1 b.wt. by the intravenous (i.v.) and intramuscular (i.m.) routes in kids and lamb. The concentrations of the drug in the plasma were measured using high-performance liquid chromatography (HPLC) with fluorescence detection. Following i.v. injection, the elimination half-life (t1/2β) in goat kids (3.57 ± 0.39 h) was higher than in lambs (2.63 ± 0.29 h). The apparent volume of distribution (Vdss) and the total body clearance (Cltot) in goat kids were 0.48 ± 0.03 l kg−1 and 0.12 ± 0.01 l kg−1 h−1, respectively. The corresponding values in lambs were 0.49 ± 0.04 l kg−1 and 0.11 ± 0.01 l kg−1 h−1, respectively. After i.m. administration, difloxacin reached a peak plasma concentration (Cmax) of 4.95 ± 0.53 and 4.25 ± 0.47 μg ml−1 at a post-injection time (Tmax) of 1.85 ± 0.23 and 1.31 ± 0.2 h in goat kids and lambs, respectively. The mean bioavailability (F) in both goat kids and lambs were 97.5 ± 20.61% and 97.1 ± 21.5%, respectively. The in vitro plasma protein binding % of difloxacin were 10.31 and 12.98 for goat kids and lambs, respectively. Using the surrogate marker Cmax/MIC and AUC24/MIC90, difloxacin could be effective by the i.m. route at 5 mg kg−1 against isolates with MIC ≤ 0.5 and 0.4 μg ml−1 for goat kids and lambs, respectively, after i.m. dosing.