Pharmacokinetic Disposition of Streptomycin Sulfate in Japanese Eel (Anguilla japonica) after Oral and Intramuscular Administrations

Pharmacokinetics and residue elimination of streptomycin sulfate (STR) are important in the determination of optimal dosage regimens and in establishing safe withdrawal periods in farmed fishes. The pharmacokinetics of STR was studied after a single dose (50 mg/kg) of intramuscular (i.m.) or oral gavage (p.o.) administration to Japanese eel (Anguilla japonica) in freshwater at 25°C. Eight fish per sampling point were examined after treatment. Plasma and muscle were collected and analyzed by high-performance liquid chromatography (HPLC) method with 0.05 μg/ml detection limit. The data of pharmacokinetics conformed to the two-compartment open model for intramuscular and one-compartment open model for oral administrations. After intramuscular administration, the elimination half-life (t1/2β) was calculated to be 11.346 h, the maximum plasma concentration (Cmax) to be 29.524 μg/ml, the time to peak plasma streptomycin concentration (Tmax) to be 0.218 h, and the area under the plasma concentration-time curve (AUC) to be 90.206 μg/ml?h. Following p.o. administration, the corresponding estimates were 13.239 h, 0.346 μg/ml, 11.960 h, and 12.356 μg/ml?h. After intramuscular administration, a therapeutic concentration of the drug was maintained for 12 hours in the plasma, however, a therapeutic level could not be achieved after oral administration, and the results suggest that the drug can be used clinically by intramuscular administration against streptomycin susceptible systemic infections in Japanese eel.