Ivermectin Toxicity in Dogs and Cats
Veterinary & Aquatic Services Department, Drs. Foster & Smith

Ivermectin and avermectin.

Anthelmintics and heartworm preventives such as Heartgard, Heartgard Plus, Ivomec, Milbemycin, and Zimectrin.

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.

The most important aspect of intoxication with avermectins is the prolonged recovery time (weeks to months).

Toxic Dose
Varies depending on age and breed.

Dogs: Ataxia, abnormal behavior, depression, vomiting, dilated pupils, and drooling. Other signs include disorientation, hyperesthesia, restlessness, stiffness, sleepiness, whining, groaning, head pressing or bobbing, aggression, chewing fits, apprehension, decrease in heart rate, seizures, hyperthermia, weakness, breathing difficulties, and cyanosis. Severe intoxication results in signs of shock, pulmonary edema, breathing difficulties, increase in heart rate, muscle tremors, coma, and death. In dogs, where ivermectin has caused death of microfilarias (immature heartworms), anaphylactic reactions may be the cause of the signs noted.

Cats: Ataxia, vocalization, disorientation, dementia, whole body tremors, dilated pupils, apparent blindness, circling, head pressing, slowed heart rate, hypothermia, coma, and death.

Immediate Action
Seek veterinary attention.

Veterinary Care
General treatment: For oral exposures, the induction of vomiting may be continued, gastric lavage is performed, and activated charcoal is administered.

Supportive treatment: IV fluids and parenteral nutrition (feeding tube or IV nutrition) are given to maintain hydration and meet caloric needs. To prevent decubital ulcers (bed sores), soft bedding (mattress) is provided, the pet is turned every few hours, and any sores that form are treated. If anaphylaxis occurs, appropriate treatment is given. Seizures and hyperthermia are controlled as necessary.

Specific treatment: Physostigmine may be administered in severe poisoning cases.

Guarded and variable.

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Keep this and all other medications out of the reach of children and pets.

If you think your pet has been poisoned...

Contact your veterinarian or one of the Animal Poison Hotlines (listed below) if you think your pet may have accidentally received or been given an overdose of the medication.

**ASPCA Animal Poison Control Center - 24-hour service available throughout North America.

1-888-4ANI-HELP (1-888-426-4435). $65.00 per case, billed to caller's credit card.

Follow-up calls can be made for no additional charge by dialing 888-299-2973.

There is no charge when the call involves a product covered by the Animal Product Safety Service.

**Pet Poison Helpline - 24-hour service available throughout North America for pet owners and veterinary professionals who require assistance with treating a potentially poisoned pet.

1-800-213-6680 ($59.00 per incident). Staffed 24-hours a day.

Updated 6/20/17

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Reprinted from PetEducation.com.