The plasma kinetics and tissue distribution of enrofloxacin and its metabolite ciprofloxacin in the Muscovy duck.

The disposition and tissue distribution of enrofloxacin and of its main metabolite ciprofloxacin were investigated in ducks after oral or intramuscular administration of a single dose of 10 mg/kg enrofloxacin. Plasma and tissue concentrations were determined by a HPLC method. The peak concentrations of enrofloxacin after intramuscular administration (1.67 micrograms/ml at 0.9 h) were higher than after an oral dose (0.99 microgram/ml at 1.38 h). The relative bioavailability of enrofloxacin after administration directly into the crop was 68%, while the metabolic conversion of enrofloxacin to ciprofloxacin was quite low (< 10%) with both routes of administration. High tissue concentrations and high tissue:plasma concentration ratios were demonstrated for enrofloxacin and ciprofloxacin 24 h after treatment. It was concluded that a dose of 10 mg/kg per day provides serum and tissue concentrations sufficiently high to be effective in the control of many infectious diseases of ducks.