What is ivermectin in heartworm preventatives?

Heartworm preventatives might be some of the most familiar medications you give your pup. But have you ever considered what they’re made of? 

Ivermectin, which is used to eliminate and treat parasites in dogs, is an ingredient in most heartworm preventatives and mange treatments. And while ivermectin is beneficial to help protect our pets, it’s essential to be mindful of the dosage and side effects, as too much of this medication can harm dogs.

‍Why do dogs take ivermectin?

If your pup takes heartworm preventatives, chances are they’re already taking ivermectin.

“Ivermectin is a medication used to treat and kill various parasites in animals. In dogs, it’s used in many heartworm preventatives, but it’s also sometimes used to treat mange. However, newer medications are used more often for treating mange now than ivermectin is,” Dr. Emily Singler, VMD, a veterinary consultant for Fetch explains.

Even though ivermectin is in heartworm preventative medication, it doesn't mean it can eliminate heartworm parasites that've already infected your dog. So, if your dog is heartworm-positive, you’ll want to talk to your veterinarian about a proper treatment solution. And it’s essential that all medications — preventive or reactive — be monitored and approved by a veterinarian to avoid negative reactions.

“If a dog is heartworm-positive, there’s a rare chance of an anaphylactic reaction when giving a dog a heartworm preventative, including those with ivermectin in them, as baby heartworms start to die,” Dr. Singler shares.

‍Ivermectin dosage for dogs

It’s crucial to only use ivermectin medications under the supervision of a vet, even in the context of prescribed heartworm preventatives, because serving the right dosage is critical to your pet’s health. “Ivermectin has a very narrow margin of safety in dogs,” Dr. Singler warns. “When properly dosed, the risk of side effects is low. Possible side effects include vomiting, diarrhea, dilated pupils and trouble maintaining balance.”

But what happens if a dog has too much ivermectin? Well, the side effects can be much worse. “It can lead to vomiting, diarrhea, blindness, seizures, other neurologic problems and even death,” Dr. Singler adds.

Your pup should be OK if you follow your vet's ivermectin dosage guidelines for your pet's specific size and age. “The standard heartworm preventive dose for ivermectin is low and generally well tolerated by all dog breeds.”

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Where should pet parents get ivermectin?

Because ivermectin is a standard treatment for parasites (it’s one that’s often administered to livestock and large animals by their parents) it’s technically available over-the-counter. But Dr. Singler emphasizes that parents shouldn’t offer this drug to their dog without a prescription and the guidance of a licensed vet who has examined their pet. 

“Dog parents should only use it in doses and formulations recommended by a veterinarian since overdosing can cause serious problems. For dogs that need to take it, the liquid formulation can be very bitter tasting, so try to follow it with something yummy,” Dr. Singler says.

When using ivermectin to treat mange in dogs, it’s important to note that a higher dose will likely be necessary. As such, it’s essential to be aware of possible drug interactions or genetic mutations that could make high doses more problematic. 

“Dogs that need to take higher doses of ivermectin for treatment of mange shouldn’t take Comfortis for flea prevention at the same time,” Dr. Singler instructs. “Also, dogs that could possibly carry the MDR-1 mutation that causes increased sensitivity to certain drugs may not tolerate high doses of ivermectin. Breeds that may carry this mutation include Australian Shepherds and related breeds. Ask your veterinarian for more guidance.”

Ultimately, ivermectin has its place in canine medical treatments, particularly for heartworm prevention and the treatment of mange. That said, dosage levels are imperative to consider, and dogs shouldn't be given ivermectin outside a licensed vet's supervision.