Anthelmintic efficacy of ivermectin in naturally parasitized cats

Ivermectin was administered per os [( PO]; n = 15) or subcutaneously [( SC]; n = 3) to naturally parasitized cats at 10 (n = 6), 100 (n = 6), or 300 (n = 6) micrograms/kg of body weight. Nontreated control cats were given sterile isotonic saline solution PO (n = 5) or SC (n = 1). Qualitative fecal examinations were performed on each cat 1 day before treatment and 14 days after treatment. Cats were euthanatized 14 days after treatment, at which time parasites from the gastrointestinal tracts were recovered, identified, and enumerated. Lungs and urinary bladders were examined histologically or by digestion (lungs only) for Capillaria spp and/or Aelurostrongylus abstrusus. Ivermectin was effective in removing Ancylostoma spp at all doses, but removal of Toxocara cati required 300 micrograms of ivermectin/kg. Efficacies against A abstrusus, Capillaria spp, and Physaloptera spp could not be determined definitively. Ivermectin had no effect on Dipylidium caninum, Hydatigera taeniaeformis, Spirometra mansonoides, or Isospora spp. Adverse reactions were not observed in cats given ivermectin PO; however, 3 cats given ivermectin SC reacted as though they experienced pain at the injection site.