Pharmacokinetics of enrofloxacin and its metabolite ciprofloxacin after intramuscular administration of enrofloxacin in goats

The pharmacokinetics of enrofloxacin and its active metabolite ciprofloxaci n were investigated in goats after a single intramuscular administration of enrofloxacin at 2.5 mg/kg body weight. The plasma concentrations of enrofl oxacin and ciprofloxacin were determined simultaneously by a HPLC method. T he peak concentrations (C-max) of enrofloxacin (1.13 mug/ml) and ciprofloxa cin (0.24 mug/ml) were observed at 0.8 and 1.2 h, respectively. The elimina tion half-life (t(1/2)beta), volume of distribution (V-d(area)), total body clearance (Cl-B) 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 t(1/2)beta, are a under the plasma concentration-time curve (AUC) and the MRT of ciprofloxa cin were 1.38 h, 0.74 mug h/ml and 2.73 h, respectively. The metabolic conv ersion of enrofloxacin to ciprofloxacin was appreciable (36%) and the sum o f the plasma concentrations of enrofloxacin and ciprofloxacin was maintaine d at or above 0.1 mug/ml for up to 4 h. Enrofloxacin appears to be useful f or the treatment of goat diseases associated with pathogens sensitive to th is drug.