Estimation of the Withdrawal Time of Levamisole in Eggs after Oral Administration to Laying Hens.

This study was conducted to evaluate withdrawal time of levamisole in eggs after oral administration in laying hens at different doses. Sampling of eggs was conducted for 37 days after the end of treatment, and levamisole concentrations were measured by liquid chromatography-tandem mass spectrometry validated according to the Commission Decision 2002/657/EC. Estimated validation parameters were as follows: decision limit, 0.54 μg/kg; detection capability, 0.56 μg/kg; limit of detection, 0.04 μg/kg; limit of quantification, 0.15 μg/kg; accuracy (recovery), between 92.9 and 102.3%; precision (relative standard deviation), ≤4.62%; and within-laboratory precision (relative standard deviation), ≤5.19%. Levamisole residue levels were significantly higher in egg yolks than in egg whites. The highest levels of levamisole were detected on day 2 posttreatment in groups receiving 50 mg/kg of body weight (556.2 μg/kg in egg yolks and 166.5 μg/kg in egg whites). Significant elimination occurred within 5 days after the cessation of treatment in all groups, with an elimination half-life of 1.3 days. Levamisole was still detectable on day 30 after the end of treatment in egg whites (0.06 μg/kg) and on day 37 in egg yolks (0.06 μg/kg). The longest withdrawal time for levamisole in eggs (14.9 days) was determined in a group treated with 25 mg of levamisole per kg of body weight for two consecutive days. According to the results, oral treatment of laying hens with levamisole may result in noncompliant egg samples even 14 days after treatment.