Liquid chromatographic determination of fenbendazole residues in pig tissues after treatment with medicated feed

Fenbendazole (FBZ) is an anthelmintic widely used in farm animals to treat parasitic infestations. In pigs, it is administered in the food. The aim of this study was to validate an analytical method for the determination of F BZ and its metabolites in pig tissues. This method is based on oxidation of FBZ and its sulfoxide metabolite to the sulfone metabolite (FBZSO(2)), The limit of quantitation for this method is 20 ng FBZSO(2)/g for all tissues. The maximum residue limits (MRLs) established for FBZ and its metabolites in pig tissues are 50 ng/g for muscle, fat, and kidney and 500 ng/g for liv er. This method is based on a liquid-liquid extraction followed by an oxida tion with peracetic acid and a cleanup procedure based on a liquid-liquid e xtractions. Determination is achieved by highperformance liquid chromatogra phy with ultraviolet detection. The present method is adjusted to the MRL e stablished for FBZ and its metabolite residues. The analysis of the residue s shows that after 72 h posttreatment, no FBZSO(2) was detected in muscle, fat, and kidney and that liver levels were below the MRL.