Pet Medication 101: Ivermectin

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Pet Medication 101: Ivermectin

It’s important to understand a medication’s uses and side effects before giving it to your pet. This medication info sheet is meant to give you a good understanding of what ivermectin is used for, how it works, and potential side effects in cats and dogs. Always consult a veterinarian before giving your pet any medication.

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1. Drug Name:


2. Brand Names:

Ivomec, Heartgard, Iverhart, Tri-Heart, Pet Trust, and Acarexx

3. How Dispensed:

Prescription and over the counter

4. Forms:

  • For heartworm prevention: tablets and chewables
  • For ear mite treatment: topical solution
  • For other parasitic treatments: oral and injectable solution

5. Drug Type/Class:

Anthelmintics (dewormer)

6. Uses in Dogs and Cats:

Monthly heartworm prevention, clearing microfilaria during active heartworm infection, ear mites, sarcoptic mange, demodectic mange, hookworms, and roundworms

7. How it Works:

Ivermectin binds to chloride channels in the nerve and muscle cells of parasites, which forces them to stay open, causing paralysis of the affected tissue and killing the parasite.

8. Side Effects and/or Signs of Overdose:

Dilated pupils and stumbling that can rapidly progress to respiratory paralysis and death if the medication is not stopped and supportive care initiated, especially in dogs with an MDR1 mutation.

MDR1 mutation: Collies, Shetland Sheepdogs, Australian Shepherds, Old English Sheepdogs, merle-colored Pomeranians, and long-haired Whippets often have a mutation in the gene that makes P-glycoprotein. This mutation allows ivermectin to cross the blood-brain barrier and can result in life-threatening complications. Normal heartworm preventatives do not use high enough doses for this to become a problem, but if a higher dose of ivermectin is being used, a commercial test kit should be used to determine if a dog has this particular mutation.

9. Drug Interactions:

Spinosad (Comfortis or Trifexis), Ketoconazole, Itraconazole, Cyclosporine, Erythromycin, Amlodipine, and Nifedipine

10. Cautionary Statements:

  • Use with extreme caution in Collies and Collie-related breeds, especially at higher doses (see MDR1 mutation notes above).
  • Ivermectin has a very bitter taste, and some animals may object or salivate excessively.
  • Oral and injectable ivermectin is not recommended for use in patients less than 6 weeks of age.
  • Never buy large animal ivermectin for use in dogs and cats without close veterinary supervision due to the potential to easily give a toxic dose with incorrect use.
  • Although ivermectin side effects usually resolve after 24 hours, side effects may persist longer in patients with liver or kidney disease.

Read more:

Heartworm Disease in Dogs and Cats

Deworming Your Dog - Q&A

Common Intestinal Parasites in Cats

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