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Collie sensitive to Heartgard? Ivermectin alternatives & Bravecto safety.

Updated On September 23rd, 2025

Pet's info: Dog | Border Collie | Male | neutered | 6 years and 5 months old | 40 lbs

I read that collies can be more susceptible to Ivermectin toxicity and I have noticed that Timo can sometimes become lethargic, lose his appetite and vomit after receiving a dose of Heartguard. My mom has continued giving it to him for years and I am very concerned. Is there an alternative that you would recommend discussing with his vet? He also takes Bravecto for flea and tick prevention. Does this contain any ingredients he may be susceptible to as well due to his genetics?

1 Answer

Most Helpful Answer

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Answered By Dr. Melanie, BVSc MS

Veterinarian

Published on June 17th, 2020

Thank you for contacting Petco Pet Education Center, formerly Petcoach with your question about Timo. Great question! You are correct that collies can be more susceptible to ivermectin, which is one of the main ingredients in Heartgard. That being said, this lethargy, loss of appetite, and vomit can all be normal side effects of the Heartgard. If he carried the gene that made him sensitive to ivermectin, I would expect to see a reaction every time he was given it, not just on occasion. I do suspect that it's normal side effects, but you should check with his vet just to be safe. The Bravest will be fine. I hope this helps!

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