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Why is my dog hiding, lethargic, and breathing fast after Trifexis?

Updated On September 23rd, 2025

Pet's info: Dog | Mixed Breed Medium (23 - 60lb) | Female | spayed | 3 years and 7 months old | 51 lbs

My dog was administered her yearly vaccines and trifexis today. It has been over 4 hours since the trifexis and she is hiding, lethargic and breathing fast. Are these normal symptoms? She has never reacted to trifexis this way.

3 Answers

Most Helpful Answer

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Answered By Dr. Melanie, BVSc MS

Veterinarian

Published on May 16th, 2019

No, this isn't typical. Keep a close eye on her, and take her back into the vet in the morning if the symptoms persist. If she starts vomiting, has diarrhea, starts having trouble breathing, gets a rash or hives, or her face starts swelling, bring her into an ER vet immediately. Best of luck.

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    Answered By Megan, DVM, CVA

    Veterinarian

    Published on May 7th, 2018

    I definitely would not continue giving Trifexis if she is continuing to have this reaction every month even if you give it on a full stomach. This is not normal and I have seen these reactions only get worse with time. I would strongly recommend you to switch her to something else like heartgard plus, advantage multi, or even the proheart injection. I would talk to your vet about what they recommend depending on the type of worms she had in the past. Different heartworm preventions work to prevent different types of worms. I hope this helps!

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    Answered By Dr. Heidi DVM, CVA, CCRT, CVTP, CVSMT, CVCH

    Veterinarian, Certified Veterinary Acupuncturist, Certified Canine Rehabilitation Practitioner

    Published on February 23rd, 2018

    While we certainly can see GI upset with heartworm preventatives, it would be very usual for a dog to have the severity of the signs that you are describing (especially when she had previously not had any problems with it), so I would recommend having your vet examine Cookie to see what they think is going on. At the very least, it sounds like she needs some medication to stop the vomiting and diarrhea. Good luck! I hope that was helpful and that Cookie feels better soon. Thanks for using Petco Pet Education Center, formerly Petcoach.

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