Erythromycin (ERY) is a drug active against Gram-positive bacteria such as Lactococcus garvieae, a pathogen responsible for an important disease that may cause a substantial decrease in rainbow trout Oncorhynchus mykiss (Walbaum) production, the species of fish most commonly produced in Italy. In the literature, studies on the kinetics behaviour of ERY in fish are limited. Therefore, the aim of the present study was to evaluate the pharmacokinetics of ERY in rainbow trout after a single oral treatment with 75 mg kg⁻¹ body weight (b.w.) of ERY and the residue depletion after multiple oral administration of 75 mg kg⁻¹ b.w. day⁻¹ of ERY for 10 days. Blood concentrations of ERY increased up to 20.24 ± 13.32 μg mL⁻¹ at 6 h, then decreased to 5.97 ± 3.89 μg mL⁻¹ at 24 h. The time during which the antibiotic remains in the bloodstream at concentrations exceeding the MIC (T > MIC) and the area under the serum concentration-time curve (AUC)/MIC are both pharmacokinetic-pharmacodynamic (PK/PD) predictors of ERY efficacy, and the data obtained allowed us to hypothesize that a dosage of 75 mg kg⁻¹ b.w. day⁻¹ of ERY could treat the lactococcosis in trout. Regarding the study of ERY depletion, rapid elimination was observed in tissue (muscle plus adherent skin); in fact the concentrations were below the limit of quantification in all samples (except two) by day 10 post-treatment. ERY is not licensed in Europe for use in aquaculture, and its use is possible only by off-label prescription with a precautionary withdrawal time of 500 degree-days, as established by Directive 2004/28/EC. From the data obtained in this study, a withdrawal time of 8.90 days was calculated, corresponding, in our experimental conditions, to 117.5 degree-days, a value significantly lower than that established by the European directive.
Keywords: erythromycin; pharmacokinetics; rainbow trout; residue depletion; withdrawal time.
© 2013 John Wiley & Sons Ltd.