Ivermectin toxicity in dogs and cats.

General Information Ivermectin is a combination of avermectins. These medications increase the activity of certain types of receptor cells in the CNS in mammals (and in the peripheral nervous system in nematodes and arthropods). This alteration of the CNS is the cause of the symptoms seen in overdose cases. Avermectins are found in the body after oral or parenteral exposure. Signs may appear within hours or may take up to 24 hours. Several breeds are more likely to be affected by avermectins including collies and collie crosses. The Old English Sheepdog, Australian Shepherds, and Shetland Sheepdogs have also been mentioned as susceptible breeds. This increased susceptibility is due to a difference in the blood-brain barrier in these breeds. Younger animals also appear more susceptible to intoxication.