Ivermectin Pharmacokinetics, Metabolism, and Tissue/Egg Residue Profiles in Laying Hens.

The goals were to determine the ivermectin (IVM) plasma pharmacokinetics, tissue and egg residue profiles, and in vitro metabolism in laying hens. Experiments conducted were (1) 8 hens were intravenously treated with IVM and blood samples taken; (2) 88 hens were treated with IVM administered daily in water (5 days) (40 were kept and their daily eggs collected; 48 were sacrificed in groups (n = 8) at different times and tissue samples taken and analyzed); (3) IVM biotransformation was studied in liver microsomes. Pharmacokinetic parameters were AUC = 85.1 ng·day/mL, Vdss = 4.43 L/kg, and T1/2el = 1.73 days. Low IVM tissue residues were quantified with the highest measured in liver and skin+fat. IVM residues were not found in egg white, but significant amounts were quantified in yolk. Residues measured in eggs were greater than some MRL values, suggesting that a withdrawal period would be necessary for eggs after IVM use in laying hens.