The plasma kinetics and tissue distribution of enrofloxacin (EF) were investigated in the seabass (Dicentrarchus labrax) after administration by oral gavage and by bath. Plasma and tissue concentrations of EF and of its metabolite ciprofloxacin (CF) were determined by HPLC, After oral treatment (5 mg/kg bw), EF was slowly absorbed and eliminated (C-max = 1.39 +/- 0.67 mu g/ml at 8 h; T-1/2 = 25 h). EF was distributed efficiently to the extravascular compartment, with concentrations in liver constantly higher than in muscle and skin. Bath treatment (5, 10 or 50 ppm for 4, 8 or 24 h) resulted in plasma and tissue levels that significantly correlated with water drug concentration or time of exposure to medicated water. CF was detected constantly in liver, occasionally in plasma, but never in muscle and skin, suggesting a low degree of metabolic conversion of EF in the seabass. After oral treatment at 5 mg/kg and bath treatment at 50 ppm for 4 h or at 5 ppm for 24 h, ratios between EF peak concentrations in plasma and tissues and MICs of EF against the most common fish pathogens exceeded those indicated as optimal to ensure the bactericidal efficacy of the drug. These dosages of EF are proposed for performing therapeutic trials in the seabass.
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