Residue depletion of erythromycin in rainbow trout and sea bream tissues

INTRODUCTION Erythromycin (ERY) is a chemotherapeutic agent proved to be active against Renibacterium salmoninarum, Lactococcus garvieae, Streptococcus iniae, Chlamydia spp. and Piscirickettsia spp. Notwithstanding it’s use is allowed in food producing animals by Regulation (EU) No 37/2010 (that establishes for fin fish tissues a maximum residue limit of 200 lg kg-1), ERY is not registered for the use in aquaculture in Europe. European legislation (Directive 2004/28/EC) allows the off-label use of drugs with a set MRL in production animals, with a precautionary withdrawal time in fish of 500C day. The aim of this study was to determine the residue depletion of ERY in tissue of trout (Oncorhynchus Mykiss) and sea bream (Sparus Aurata) after oral treatment at real field conditions, in order to calculate its effective withdrawal time in the two species. MATERIALS AND METHODS One hundred sixty five trout and 165 sea bream were treated for 10 consecutive days with medicated feed containing ERY in such amount that dispensed at the rate of 1% of the biomass a nominal dose of 75 mg kg-1 b.w. was provided. Throughout the experimental period, trout and sea bream were farmed at 13.2 and 26.5C respectively. Samples of tissue plus adherent skin (from 15 fish at each scheduled sample time) were taken at 8 h, 1, 2, 3, 5, 7, 10, 15, 20, 25 and 30 days after the last treatment. After extraction from tissues, performed following a published analytical method (Lucchetti, 2005) the quantitative analysis of ERY was performed by an Agilent 6540 UHD accurate mass Q-TOF LC/MS. The withdrawal time was calculated using the Withdrawal Time Calculation Program WT1.4 (EMEA, London, UK). RESULTS The concentrations-time profiles of ERY in trout and sea bream tissues are reported below. For the calculation of withdrawal time, concentrations below the LOQ (50 ppb) were considered equal to LOQ/2. For trout, withdrawal time was calculated using six sample times: the 10th and 15th day were not considered, since ERY concentrations in 12 and 13 of the 15 fish in the respective sample times were below LOQ. The rapid depletion of ERY from sea bream tissues did not allowus to plot data in theWT1.4 program.For trout, awithdrawal time of 8.90 dayswas calculated, corresponding with a temperature of 13.2–117.5C day. CONCLUSIONS The rapid drop of ERY concentration below the MRL in sea bream is probably due to its rapid absorption and elimination from fish, as experienced by the same Authors in a previous pharmacokinetic study. The withdrawal time obtained for trout, far lower than 500C day, renders ERY extremely safe for human consumers after its off-label use in this fish species. REFERENCES 1. Lucchetti,D.,Fabrizi,L.,Esposito,A.,Guandalini,E.,DiPasquale, M. & Coni, E. (2005) Simple confirmatory method for the determination of erythromycin residues in trout: A fast liquidliquid extraction followed by liquid chromatography-tandem mass spectrometry. J. Agric. Food Chem., 53, 9689–9694.