EFFICACY OF IVERMECTIN IN A BEEF-BASED CHEWABLE FORMULATION AGAINST ANCYLOSTOMA-CANINUM AND UNCINARIA-STENOCEPHALA IN DOGS

The effective dosage of a chewable formulation of ivermectin was deter mined in 35 young dogs with induced infections of Ancylostoma caninum and Uncinaria stenocephala. Dogs were inoculated with these parasites and held until the infections were patent. Within each of 7 replicates , dogs were allocated randomly to 1 of 5 treatment groups: vehicle con trol, or ivermectin at 6, 12, 18, or 24 mug/kg. Chewable treatments we re tailored to body weight. Seven or 8 days after treatment, parasites were recovered using standard techniques. All 7 controls had adult A. caninum (geometric mean = 35.5) and U. stenocephala (geometric mean = 82.6). Against A. caninum, the efficacy of ivermectin was 52%, 98%, 9 5%, and 97% at 6, 12, 18, and 24 mug/kg, respectively. The statistical model that best described the dose response was linear to 42 mug/kg w ith a plateau thereafter. Using this model, the estimated reduction fr om the predicted control mean was 97.2%; the estimated dose to elimina te 90% of the worms (ED90) was 8.4 mug/kg, and the ED95 was 10.5 mug/k g. Against U. stenocephala. the dose response was linear in the range studied, with an ED90 of 20.8 mug/kg; at 24 mug/kg, it was estimated t hat 93.2% of the worms would be eliminated.