Relationship between ivermectin concentrations at the injection site, muscle and fat of steers treated with traditional and long-acting preparations

Abstract

Ivermectin (IVM) is broad-spectrum compound active against endo and ecto-parasites of clinical relevance in veterinary and human medicine. It is commercially available to use in livestock animals as injectable formulations containing 1% IVM and also as a concentrated (3.15%) long-acting (LA) preparation. The potential risk of the presence of high concentrations of drug residues in muscle tissue at the injection site is therefore a concern. The aim of this study was to determine the relationship between the IVM residual concentrations at the injection site, in comparison to the untreated contralateral neck (control muscle) and in fat from cattle treated with different preparations. Healthy steers received one of the following subcutaneous treatments in the neck area: Group A: IVM-LA 3.15% preparation and Group B: IVM 1%. After a withdrawal period for each formulation the animals were sent to the slaughterhouse. IVM concentrations at the injection site were detected among animals treated with the LA formulation, with high residual concentrations of IVM (between 15 and 141 μg/kg) in the injection site of two steers. However, the residual concentrations of IVM at the injection site obtained after the subcutaneous administration of the LA preparation do not represent a toxicological risk to consumers.