Pharmacokinetics of Enrofloxacin and Its Metabolite Ciprofloxacin after Intramuscular Administration of Enrofloxacin in Goats

The pharmacokinetics of enrofloxacin and its active metabolite ciprofloxacin were investigated in goats after a single intramuscular administration of enrofloxacin at 2.5 mg/kg body weight. The plasma concentrations of enrofloxacin and ciprofloxacin were determined simultaneously by a HPLC method. The peak concentrations (Cmax) of enrofloxacin (1.13 μg/ml) and ciprofloxacin (0.24 μg/ml) were observed at 0.8 and 1.2 h, respectively. The elimination half-life (t1/2β), volume of distribution (Vd(area)), total body clearance (ClB) and mean residence time (MRT) of enrofloxacin were 0.74 h, 1.42 L/kg, 1329 ml/h per kg and 1.54 h, respectively. The t1/2β, area under the plasma concentration–time curve (AUC) and the MRT of ciprofloxacin were 1.38 h, 0.74 μg h/ml and 2.73 h, respectively. The metabolic conversion of enrofloxacin to ciprofloxacin was appreciable (36%) and the sum of the plasma concentrations of enrofloxacin and ciprofloxacin was maintained at or above 0.1 μg/ml for up to 4 h. Enrofloxacin appears to be useful for the treatment of goat diseases associated with pathogens sensitive to this drug.