Residues of Oxytetracycline and Its 4′-Epimer in Edible Tissues from Turkeys

Abstract

Abstract Residues of oxytetracycline (OTC) in edible tissues (muscle, liver, and kidney) of 18 turkeys were determined after continuous administration of the drug for 3 days in drinking water at the maximum recommended concentration of 400 mg/L. The European Union (EU) maximum residue limits (MRLs) set for OTC are 100 μg/kg in muscle tissues, 300 μg/kg in liver, and 600 μg/kg in kidney, as the sum of the parent compound and its derivative 4′-epi-oxytetracycline (4-epi-OTC). Cleanup of tissue samples was performed by metal chelate affinity chromatography (MCAC), but the original technique was miniaturized by the adoption of a mini solid-phase extraction column, allowing reduction of solvents, time, and hazardous waste. OTC and its 4′-epimer were quantitated by an isocratic liquid chromatography elution with UV detection. After 1 day of withdrawal, OTC plus 4-epi-OTC residues were greater than MRL values in muscle and liver; 3 days after the end of treatment, all tissue residues were far lower than the MRL values. At the first day after the end of treatment, 4-epi-OTC was detected at very low concentrations only in muscle, in liver after 1 and 3 days of withdrawal, and in kidney at all sampling times. The withdrawal time was calculated according to EU recommendations and was set at 5 days.