Disposition kinetics of moxifloxacin in lactating ewes

The present study was planned to investigate the plasma disposition kinetics and the pattern of moxifloxacin elimination in the milk of lactating ewes (n = 6) following a single intravenous (IV) bolus or intramuscular (IM) injections at a dosage of 5 mg/kg in all animals. A crossover study was carried out in two phases separated by 21 days. Plasma and milk samples were collected serially for 72 h and moxifloxacin concentrations were assayed using high performance liquid chromatography with fluorescence detection. A two-compartment open model best described the decrease of moxifloxacin concentration in the plasma after IV injection. The disposition after IM administration moxifloxacin was best described by a one-compartment model. Following IV administration, the distribution half-life (t1/2α) was 0.22 ± 0.02 h. The elimination half-life was 1.77 ± 0.23 h. The volume of distribution at steady state (Vdss) was 0.84 ± 0.12 L/kg, the total body clearance (Cltot) was 0.34 ± 0.04 L/h/kg and the area under the curve (AUC) was 14.74 ± 2.16 μg h/mL. Following IM administration, the mean Tmax, Cmax, t1/2el and AUC values for plasma data were 1.45 ± 0.02 h, 2.21 ± 0.27 μg/mL, 2.68 ± 0.19 h and 14.21 ± 2.35 μg h/mL. The IM bioavailability was 96.35 ± 17.23% and the in vitro protein binding of moxifloxacin ranged from 32–37%. Penetration of moxifloxacin from the blood into milk was rapid and extensive, and the moxifloxacin concentrations in milk exceeded those in plasma from 1 h after administration. The kinetic values AUCmilk/AUCplasma and Cmax milk/Cmax plasma ratios indicated a wide penetration of moxifloxacin from the bloodstream to the mammary gland. The in vitro minimum inhibitory concentration (MIC) of moxifloxacin for Mannheimia haemolytica was found to be 0.035 μg/mL.