Some pharmacokinetic parameters of pefloxacin in lactating goats

The aim of this study was to elucidate some of the pharmacokinetic parameters of pefloxacin in lactating goats (n = 5) following intravenous (i.v.) or intramuscular (i.m.) injections of 10 mg/kg bw. Serially obtained serum, milk and urine samples were collected at precise time intervals, and the drug concentrations were assayed using a microbiological assay. A two-compartment open model best described the decrease of pefloxacin concentration in the serum after intravenous administration. The maximum serum concentration (C0(p)) was 8.4 +/- 0.48 microg/ml; elimination half-life (t 1/2 beta) was 1.6 +/- 0.3 h; total body clearance (Cl(tot) was 3.6 +/- 0.3 L/kg/h; steady-state volume of distribution (V(dss)) was 5.14 +/- 0.21 L/kg; and the area under the curve (AUC) was 2.78 +/- 0.22 microg.ml/h. Pefloxacin was absorbed rapidly after i.m. injection with an absorption half-life (t 1/2 ab) of 0.32 +/- 0.02 h. The peak serum concentration (Cmax) of 0.86 +/- 0.08 microg/ml was attained at 0.75 h (Tmax). The absolute bioavailability after i.m. administration was 70.63 +/- 1.13% and the serum protein-bound fraction ranged from 7.2% to 14.3%, with an average value of 9.8 +/- 1.6%. Penetration of pefloxacin from the blood into the milk was rapid and extensive, and the pefloxacin concentration in milk exceeded that in serum from 1 h after administration. The drug was detected in milk and urine for 10 and 72 h, respectively; no samples were taken after 72 h.