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 groups of 8 laying hens feed with approximately 3, 10 and 30 mg kg-1 flubendazole for 21 days. Eggs were sampled during this period and one week after the administration. Samples of both whole egg and egg white/yolk were analysed separately. Flubendazole analysis was performed by reversed phase HPLC and 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 kg-1. Both the hydrolysed and reduced metabolites of flubendazole were also determined quantitatively. The eggs of control hens housed in the same room during the study period did not contain any detectable flubendazole or metabolite 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 LOD. 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 days and there was a good dose response relation between levels in feed and those in eggs. The residues of parent compound and metabolites almost exclusively occurred in yolk, the metabolites accounting for some 60-65% of the total residue. The residues of the parent compound and its metabolites declined below 100 micrograms kg-1 5 days after the administration of dosed feed had ended.