Abstract
Turbot (Scophthalmus maximus) is a traditionally farmed species in Europe. Although it was introduced to China in 1992, it has become an important aquaculture species in coastal areas of northern China, especially in the Jiaodong Peninsula, Shandong Province. Recently, more and more epizootic diseases of farmed turbot in China occurred because of high density stocking and improper management. Enrofloxacin, a “third-generation” member of the quinolone family, it has been also used widely to prevent or treat bacterial diseases in fish farming in many countries. And it has previously been studied in Seabass (Dicentrarchus labrax), fingerling Rainbow Trout (Oncorhynchus mykiss), Atlantic Salmon (Salmo salar), Red Pacu (Colossoma brachypomum) and Koi Carp (Cyprinus carpio), ect. However, to our knowledge, there are no studies concerning the pharmacokinetics of enrofloxacin in turbot. So the purpose of this study was to compare the pharmacokinetics of enrofloxacin in plasma of turbot after intramuscular and oral administration to establish the scheme of enrofloxacin, at the water temperature of (16±0.6)℃, and generate data in muscle, liver and kidney to establish a reasonable withdrawal period for enrofloxacin in farmed turbot. Six turbot were randomly selected from the tank and sampled at 5, 15, 30min and 1, 2, 4, 6, 8, 12, 16, 24, 36, 48, 72 and 96h after the last intramuscular and oral administration, respectively. The concentration of enrofloxacin were determined by the High Performance Liquid Chromatography, the isocratic mobile phase consisted of a phosphoric acid (0.01mol/L)-acetonitrile (80:20 v:v), adjusted to pH 3.42 with triethylamine, at a flow-rate of 1mL/min. The agilent Tc-C18 (5μm, 4.6×25mm) was used and the fluorescence detector was set at 278 nm and 460 nm as excitation and emission wavelengths, respectively. The percentage recoveries of enrofloxacin were all higher than 81.16% for plasma, liver, kidney and muscle, the intra-day precision of the analytical method for samples (three replications) was 0.29%-2.03%, the inter-day precision was 2.06%-5.10%, the detection limits of enrofloxacin was 0.01μg/g (μg/mL). The data were analyzed with the pharmacokinetic program DAS2.0. The results showed that the plasma concentration-time data for enrofloxacin were best described as a two-compartment open model with first-order absorption and elimination after intramuscular and oral administration, the pharmacokinetic equation was: Cim=10.237e-0.702t+6.151e-0.01t-16.388e-25.796t and Cpo=3.701e-0.072t+3.534e-0.007t-7.235e-0.364t, respectively. After administration by intramuscular and oral, the main pharmacokinetic parameters were as follows: t1/2Ka 0.027h and 1.904, tmax 0.5h and 4h, t1/2α0.987h and 9.621h, Cmax 21.7172μg/mL and 5.3594μg/mL, F 88.57% and 66.42%, t1/2β 68.003h and 99.137h, respectively. It indicated that more quickly absorption, higher peak plasma concentration, higher bioavailability and faster elimination after intramuscular administration than by oral administration. It was found that those two routes of enrofloxacin administration to turbot were effective since the concentrations of drug in plasma were greater than minimal inhibitory concentration of most fish bacterial pathogens, under this experiment condition. The scheme of enrofloxacin was established to fish bacterial diseases, with the dose of 19.05mg/kg at the interval of 2d, by intramuscular; and 13.92mg/kg at the interval of 1d, by oral administration. As an edible tissue, muscle was selected as target tissue in the experiment, the withdrawal periods, which should not be less than 30d and 45d flowing intramuscular and oral administration, respectively, was established according to the MRL by using elimination parameters and equations.
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