Pharmacokinetics and tissue distribution of enrofloxacin and its metabolite ciprofloxacin in Scylla serrata following oral gavage at two salinities

The pharmacokinetics of enrofloxacin and its metabolite ciprofloxacin were investigated in the mud crab (Scylla serrata) kept at two salinities of 4 ppt and 33 ppt after a single oral gavage of 30 mg enrofloxacin per kg body weight. The concentrations of enrofloxacin and ciprofloxacin in the main tissues (hemolymph, muscle and hepatopancreas) were simultaneously detected by HPLC. The parameters in hemolymph and tissues were calculated by non-compartment model based on statistic moment theory. Area under the concentration-time curve from 0 to ∞ h (AUC0-∞), apparent volume of distribution (Vz), half-life (t1/2z), body clearance (CLz) and mean residue time from 0 to ∞ h (MRT0-∞) in hemolymph were 1628.6 μgh/ml, 1.73 L/kg, 65.09 h, 0.018 L/h/kg and 83.72 h, respectively, at 4 ppt, and 3251.4 μgh/ml, 1.547 L/kg, 116.22 h, 0.009 L/h/kg and 160.66 h, respectively, at 33 ppt. Peak levels of enrofloxacin in hepatopancreas were much higher than those in the hemolymph and muscle, at both salinities. Comparative pharmacokinetics in hemolymph, muscle and hepatopancreas showed slower elimination of enrofloxacin at 33 ppt than at 4 ppt. The AUC ratios of ciprofloxacin and enrofloxacin in mud crab hemolymph at 4 ppt and 33 ppt were only 4.0% and 3.8%, respectively. Mean residue time (MRT) and body clearance (CLz), deriving from statistical moment theory, indicated that ciprofloxacin eliminated slower at 33 ppt than at 4 ppt, the same as enrofloxacin.