Flubendazole residues in eggs after oral administration to laying hens: determination with reversed phase liquid chromatography

Flubendazole residues in eggs were experimentally induced by providing grou ps of 8 laying hens feed with approximately 3, 10 and 30 mg kg(-1) flubenda zole for 21 days. Eggs were sampled during this period and one week after t he administration. Samples of both whole egg and egg white/yolk were analys ed separately. Flubendazole analysis was performed by reversed phase HPLC a nd UV detection at 250 nm (eggs) or 320 nm (feed). The limit of detection ( LOD) for flubendazole in feed was 0.3 mg kg(-1) and in whole egg 0.012 mg k g(-1). Both the hydrolysed and reduced metabolites of flubendazole were als o determined quantitatively. The eggs of control hens housed in the same ro om during the study period did not contain any detectable flubendazole or m etabolite residue. The eggs from the lowest dosed group (3 mg kg(-1) feed) did contain residues, but most of them were only slightly higher than the L OD. Residues in eggs collected from the laying hens that obtained feed with 10 and 30 mg kg(-1) flubendazole reached a plateau level after some 10 day s and there was a good dose response relation between levels in feed and th ose in eggs. The residues of parent compound and metabolites almost exclusi vely occurred in yolk, the metabolites accounting for some 60-65% of the to tal residue. The residues of the parent compound and its metabolites declin ed below 100 mu g kg(-1) 5 days after the administration of dosed feed had ended.