Pharmacokinetics of ivermectin administered intravenously to cattle.

Ivermectin, a macrocyclic lactone disaccharide antiparasitic agent, was administered intravenously to six young calves (one bull, five steers) as a bolus dose of 200 micrograms/kg. The disposition kinetics of ivermectin in cattle can be described by a three-compartment open model with elimination from the central compartment. Compartmental analysis yielded mean parameters as follows: terminal elimination rate constant (beta) = 0.258 d-1, biological half-life (t 1/2 beta) = 2.7 d; apparent volume of distribution of the central compartment (Vd1) = 0.45 L/kg; apparent volume of distribution at steady state (Vdss) = 2.4 L/kg. The area under the plasma concentration-time curve (AUC) was 254 ng X d/mL. Noncompartmental parameters, obtained by utilizing statistical moment theory, mean residence time (MRT), clearance (CL), and Vdss were calculated to be 2.8 d, 0.79 L/kg X d, and 2.2 L/kg, respectively.