Ivermectin for Cats: Overview, Dosage & Side Effects

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Ivermectin is a prescription-only drug used to treat parasites in cats and other animals. You are most likely to use ivermectin in your cat to prevent heartworm infection, using a monthly tablet (Heartgard). But your veterinarian might also prescribe ivermectin for a variety of other parasites, including ear mites and scabies.

Ivermectin comes in tablet, liquid (for use in the ear), and injectable forms. Ivermectin is quite safe for cats when used at recommended doses but can have serious side effects at high doses.

Ivermectin for Cats Overview

Medication Type:
Medication Form:
Tablets and topical liquid (ear drops); injectable forms licensed for use in farm animals.
Brand Names:
Heartgard and Acarexx otic suspension licensed for use in cats. Various products licensed for use in farm animals.
Licensed for preventing heartworm and treating ear mites in cats in the United States. Also effective against other internal and external parasites off-label, including scabies.
Available Dosages:
Heartgard tablets 55 micrograms (up to 5 pounds) and 165 micrograms (5 to 15 pounds). Acarexx otic suspension 0.01% solution. Injectable 10 milligrams/milliliter various products licensed for use in farm animals.
Potential Side Effects:
Few when used at appropriate doses. Vomiting (less than 0.2% of cats) and diarrhea (less than 0.3% of cats).
Do not use in kittens younger than 6 weeks of age.
Avoid using alongside benzodiazepines, ketamine, erythromycin, spinosad, or certain anti-fungal treatments.

About Ivermectin for Cats

Ivermectin is most commonly used in cats to prevent heartworm infection. Heartworm is a serious disease caused by worms called Dirofilaria immitis. Your cat can be infected after being bitten by an infected mosquito. Heartworm infection can cause coughing, breathing problems, and non-specific signs such as weight loss or vomiting. Sadly, in severe cases, it can cause sudden death.

Heartworm infection is difficult to treat, so it is better to prevent your cat from being infected. To prevent heartworm, you can give your cat an ivermectin tablet (Heartgard) at home every month.

Ivermectin can also be used to treat other internal and external parasites in cats, such as ear mites and scabies. It is not effective against fleas or tapeworms.

Ivermectin Dose for Cats

Ivermectin is approved by the FDA in cats for preventing heartworm, using Heartgard tablets. They recommend a minimum dose of 12 micrograms/pound once a month. However, you should speak to your veterinarian about testing your cat for active heartworm infection before starting preventative treatment.

Cat Weight Tablets per month Strength
Up to 5 pounds 1 55 micrograms
5 to 15 pounds 1 165 micrograms

The FDA has also approved an ivermectin solution for treating ear mites in cats, called Acarexx otic suspension.

Heartgard Oral Tablets

Heartgard tablets are the licensed product for preventing heartworm in cats older than 6 weeks old. They come in two tablet sizes: 55 micrograms (for cats up to 5 pounds) and 165 micrograms (for cats 5 to 15 pounds). Give your cat one tablet a month year round.

You must give the first dose within 30 days of your cat’s first possible exposure to mosquitoes. The last dose should be given no later than 30 days after their last possible exposure. Try to give Heartgard on the same day each month to make sure they are effective.

Monthly treatment with Heartgard will also protect your cat against infection with hookworm.

Acarexx Otic Suspension

Acarexx otic suspension contains 0.01% ivermectin and is used to treat adult ear mites in cats and kittens older than 4 weeks of age. Your vet will administer 0.5 milliliters of liquid into your cat’s ear canal. Usually, one dose is effective. But your vet might repeat the treatment once more if needed.

Off-Label Use of Ivermectin

Your vet may also use ivermectin “off-label” at differing doses and formulations to treat other parasites in your cat, such as scabies. This means they are using it in a way that is not what the FDA originally approved it for. For example, your veterinarian might use an injection of ivermectin that is licensed in farm animals to treat ear mites or scabies in your cat.

How To Administer Ivermectin to Cats

Cute cat eating from bowl

Heartgard (ivermectin) comes as a chewable tablet that can be given to your cat as a treat or mixed into food.

If you are administering ivermectin to your cat at home, this will most likely be Heartgard tablets. As Heartgard tablets are chewable, you can offer the tablet to your cat in your hand or mixed with a small amount of their food.

However, if your cat will not eat the tablet, you can break it into pieces and give it directly into their mouth. Take care to ensure your cat has eaten the whole tablet. If you think they haven’t, it is best to give them a new one.

Side Effects of Ivermectin for Cats

When used at appropriate doses, ivermectin is very safe for cats. There is a small chance your cat might experience vomiting or diarrhea. However, in clinical trials, this was only seen in less than 0.3% and less than 0.2% of cats respectively.

If you think your cat does experience a side effect from ivermectin, contact your veterinarian for advice. You should also report the suspected reaction to the manufacturer, Boehringer Ingelheim Animal Health USA.

Overdose and Emergencies

Ivermectin has a wide safety margin in cats, meaning overdoses with heartworm prevention tablets are rare. Of course, if your cat does ingest more than the recommended amount you should contact your veterinarian for advice.

However, ivermectin is often used off-label in cats using formulations designed for much larger animals such as cattle, sheep, and horses. Unfortunately, it is not uncommon that cats are overdosed when these products are used at an inappropriate dose, as they contain such high concentrations. Cats can also suffer from ivermectin overdose by accidentally ingesting these large animal formulations. For instance, licking unused horse wormer from the syringe.

If your cat ingests an overdose of ivermectin they might show signs within two to three hours. But symptoms can also develop more slowly in less serious cases. Symptoms of ivermectin toxicosis include:

Cats suffering from ivermectin toxicosis need immediate and intensive veterinary treatment.

Potential Drug Interactions With Ivermectin

veterinary giving the vaccine to the cat

Cats should not use ivermectin if they are also taking benzodiazepines, ketamine, erythromycin, spinosad, or certain anti-fungal treatments.

Ivermectin is used safely in cats receiving common vaccinations, antibiotics, steroids, and other antiparasitics. However, it is important to let your veterinarian know about any treatment (including herbal or nutritional supplements) that your cat is taking before they prescribe ivermectin.

In particular, avoid using ivermectin in your cat if they are being treated with benzodiazepines, ketamine, erythromycin, spinosad, or certain anti-fungal treatments.

How To Store Ivermectin

Store ivermectin products at room temperature away from direct sunlight. Always return the remaining tablets in their blister-backed foil into the package after use to protect them from light.

Related Conditions

Frequently Asked Questions

Is ivermectin safe for cats?

When used at an appropriate dose, ivermectin is very safe to use in cats. The FDA has approved ivermectin to prevent heartworm in cats at a minimum dose of 12 micrograms/pound once a month. Ivermectin has a wide safety margin in cats, with single-dose tolerance studies showing a 30-fold safety margin over the minimum recommended dosage.

Why is ivermectin given to cats?

Ivermectin is most commonly given to cats to prevent heartworm infection. It can also be used to treat a variety of other internal and external parasites, including ear mites and cat scabies. This use is often "off-label," meaning it is being used to treat something other than what the FDA approved it for.

Is ivermectin good for deworming cats?

Ivermectin is mostly used to prevent heartworm in cats. Although it can be used to prevent other types of worms (such as roundworms), other types of wormers are more commonly used. Ivermectin is not effective against tapeworms.

How much ivermectin can you give a cat?

The FDA has approved ivermectin to prevent heartworm in cats at a minimum dose of 12 micrograms/pound once a month. It can be used off-label at a range of doses to treat other internal and external parasites. Signs of ivermectin toxicosis have been reported at doses over 100 micrograms/pound.

What happens if you give a cat too much ivermectin?

Signs of ivermectin overdose in cats can develop in as little as two to three hours after ingestion. They include depression, weakness, enlarged pupils, blindness, lack of coordination, tremors, and collapse. Cats suspected of ivermectin overdose should be taken to a veterinarian immediately.

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  1. Heartgard prescribing information: https://docs.boehringer-ingelheim.com/PI/Paras/Heartgard_for_Cats_PI_with_BI_logo_-2020.pdf

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About Dr. Nat Scroggie MRCVS

Nat is a keen runner and has a passion for wellbeing, both within and outside the veterinary profession where she works hard to support others in their own wellbeing. She lives in Nottingham with her partner, their young baby and their beloved 14 year old lab x collie, Milly.