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Ivermectin / Heartgard®

Updated: Dec 9, 2021

In dogs, ivermectin is FDA-approved only for use as a preventative for heartworm. In cats, it is FDA-approved for heartworm prevention and control of hookworms. It has also been used as a microfilaricide, ectoparasiticide, and endoparasiticide. Ivermectin and doxycycline individually suppress embryogenesis and weaken adult heartworms and when used together provide more rapid adulticidal activity than either drug alone. The American Heartworm Society does not recommend using macrocyclic lactones at prophylactic doses as a slow-kill adulticide method for D. immitis


Ivermectin is not recommended for use in puppies less than 6 weeks old. After receiving heartworm prophylaxis doses, the manufacturer recommends observing Collie-type breeds for at least 8 hours after administration. Secondary to a defective blood-brain barrier, ABCB1-1Δ (MDR1-allele) mutant/mutant dogs can show adverse neurologic signs after a single doses >120 micrograms/kg and develop life-threatening neurologic toxicity at doses of 300 micrograms/kg (Mealey 2013). When used at extra-label dosages in dogs, most clinicians feel that ivermectin should not be used in breeds susceptible (Collies, Shelties, Australian shepherds, etc.) to the ABCB1-1Δmutation unless the patient has been tested and found not to have the gene defect. A specific test for identifying dogs that have the gene defect is available; contact the veterinary clinical pharmacology lab at At higher dosages, neurotoxicity can occur rarely in dogs tested normal/normal so it is advised to continually monitor for adverse effects. When used at labeled heartworm preventative dosages, toxicity is rarely observed. It is recommended that should they occur, ivermectin be discontinued.


As a preventative for heartworm

As adjunctive treatment for heartworm disease

As an ectoparasiticide

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