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My dog reacted to Trifexis. Is Interceptor safe after neutering?

Updated On September 23rd, 2025

Pet's info: Dog | Mixed Breed | Male | neutered | 9 months and 24 days old | 10 lbs

My pup had an allergic reaction to Trifexis about 2 months ago. We wanted to restart on a heart worm med so we got a RX for interceptor. Just realized some similar ingredients. Would it be safe to give him or should I stay clear of anything similar?? Also he was just neutered on 7/20 & still sore. Don’t want him to feel sick too if not necessary. Thank u!

2 Answers

Most Helpful Answer

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Answered By Stacey Anstaett, DVM

Veterinarian

Published on July 23rd, 2018

One of the active drug ingredient in both meds is milbemycin, so if the allergy or reaction to was that specific drug, it would be better to avoid it. Of course we can't know that for sure. It may be that Rexy is allergic to one of the other active ingredients in trifexis, or to one of the inert ingredients. However, I think the best recommendation would be to use a prevention that does NOT contain milbemycin or praziquantel (the ingredients in Trifexis). Heartgard is a good alternative. Make sure that he is up to date on his heart worm test first. I think its fine to go ahead and get him started on a different heart worm prevention ASAP, even though he just had surgery. I hope that helps you ! Thanks for asking Petco Pet Education Center, formerly Petcoach!

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    Answered By Dr. Melanie, BVSc MS

    Veterinarian

    Published on July 23rd, 2018

    The active ingredients in Trifexis are spinosad and milbemycin oxime. The active ingredient in Interceptor is milbemycin oxime. Milbemycin oxime is used to prevent heartworm disease, and it could be your littlest dog had a reaction to the spinosad. I would try the Interceptor, but monitor him closely for an allergic reaction. I hope this helps!

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