Parasite Drug (Ivermectin) Poisoning in Dogs

Ivermectin toxicosis is uncommon in dogs overall. Some dogs have a multidrug resistance mutation (MDR1) that makes them highly sensitive to ivermectin toxicosis. The MDR1 mutation is common in collies, but any dog can be affected. Most commercially available canine genetic tests screen for the MDR1 mutation, allowing for early identification of sensitive dogs. Ivermectin toxicosis is much more common in dogs with the MDR1 mutation because they become sick at lower doses. Dogs showing symptoms of ivermectin toxicosis require emergency veterinary care, as the toxicosis can lead to respiratory failure, loss of consciousness, or death.

Ivermectin toxicosis primarily varies in the amount of drug consumed, with higher doses producing more severe intoxication. Dogs with severe ivermectin toxicosis may experience additional symptoms.

Ivermectin is a common active ingredient in heartworm preventives. The dose of ivermectin in these products is very low and safe for use in dogs with the MDR1 gene mutation. These products are usually formulated into flavored chewables, however, so a small dog who comes across a large supply of heartworm pills could potentially end up experiencing toxicosis.

Ivermectin toxicosis occurs as a result of exposure to a toxic dose of ivermectin, usually via oral administration or injection. Another common route of exposure is the ingestion of livestock feces after the large animal has been treated with ivermectin.

Ivermectin toxicosis is more likely to occur in dogs with the MDR1 mutation because they develop toxicosis at much lower doses.

Recommended doses of ivermectin vary widely depending on the intended use. Veterinary direction and oversight is critical for appropriate use of this potentially lethal medication.

Ivermectin toxicosis arises from the drug crossing into the nervous system, particularly affecting the brain.

Diagnosis of ivermectin toxicosis primarily relies on a history of receiving or having access to an ivermectin-containing product, combined with the symptoms identified on a physical exam. There is no specific test to identify ivermectin toxicosis.

Treatment primarily relies on supportive care until the drug is removed from the body.

Note: Induction of vomiting or administration of activated charcoal should only be performed by a veterinarian. There is no safe way to induce vomiting or administer activated charcoal at home.

Supportive care may involve:

• Activated charcoal to bind the drug and prevent further absorption
• IV fluids with electrolytes
• Medications to increase heart rate
• Anti-seizure medications
• Nutritional support
• Rotating the patient frequently if they are unable to stand or sit on their own
• Eye lubricants in dogs unable to blink
• Mechanical ventilation in dogs that stop breathing

The prognosis of ivermectin toxicosis depends on the amount of drug ingested, the individual sensitivity of the affected dog, the overall health of the dog prior to ingestion, and whether symptoms respond to treatment. Overall, the prognosis is fair to good with appropriate supportive care. In some cases, dogs require several weeks of hospitalization and supportive care to recover. Dogs that recover have no long-term effects from the toxicosis.

Ivermectin toxicosis can be prevented by consulting a veterinarian prior to giving any ivermectin-containing product to a dog. Consultation ensures that an appropriate medication with an appropriate dose is being used for the individual dog requiring treatment. Storing ivermectin-containing products to prevent pet access is also beneficial.

Most commercially available canine genetic tests screen for the multidrug resistance-1 gene mutation (MDR-1). This allows for identification of ivermectin sensitivity in dogs.

Ivermectin-sensitive dogs who reside on farms where animals are treated with ivermectin can develop toxicosis after ingesting herbivore feces. Restricting access to herbivore feces after the animals are treated with ivermectin can help prevent toxicosis. Ivermectin toxicosis is uncommon in dogs, however is significantly more common in ivermectin-sensitive breeds such as Collies.

Ivermectin toxicosis is uncommon in dogs, however is significantly more common in ivermectin-sensitive breeds such as Collies.

Supportive care