How Does Ivermectin Work on a Dog?

Ivermectin kills the heartworm larvae that mosquitoes spread.
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Ivermectin is an anti-parasitic medication used to treat a broad spectrum of parasites, including Demodex mites and heartworm larvae. Ivermectin works by causing neurological damage to the parasites, results in their paralysis or death. Unfortunately, Ivermectin does not come without considerations. Certain breeds should not take the medication.

Demodex Mites

Demodex mites are normal on the skin of most dogs. Typically, these mites live and feed off the natural oils in the skin but never cause problems for the canine host. Occasionally, a mite population can result in demodectic mange. In this case, Ivermectin offers relief from the increased population by killing the mites.


Heartworm is caused by the parasitic worm Dirofilaria immitis. Female mosquitos transfer the larvae into dogs, and they migrate into the blood vessels and heart. Heartworm medications offer a preventative treatment for heartworm that works by killing the larvae. Heartworm medications come in four different varieties, with Ivermectin-based products being one option.


Certain breeds have an apparent sensitivity to Ivermectin that allows the medication to pass the blood-brain barrier and enter the central nervous system, often proving fatal. Large doses, such as needed for Demodex treatments, should be avoided in sheepdogs, shepherds, collies, Skye terriers, silken windhounds and long-haired whippets. The amount used in heartworm medications is typically safe enough for any breed.