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Why is my dog having bloody diarrhea after heartworm treatment?

Updated On September 23rd, 2025

Pet's info: Dog | German Shepherd | Female | unspayed | 8 years and 9 months old | 78 lbs

My vet has Dose 1 of Heartworm treatment Vaccine on the 16th and Dose 2 of the shot on the 17th and has been diarrheaing with blood ever since and it's frequently. Is this normal?

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1 Answer

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Answered By David Darvishian

Veterinarian

Published on August 23rd, 2021

Hello and thank you for using Petco Pet Education Center, formerly Petcoach! Sorry Hanna is having problems post heartworm treatment. Diarrhea with blood can be caused by many things. One very common problem in adult dogs that causes bloody diarrhea is a whipworm infection. Other causes include food intolerance/sensitivity, dietary indiscretion, parasites, drug reactions, stress, infection, etc. I would advise calling your veterinarian to investigate this problem and make sure that Hanna is ok after receiving the injections for heartworm. Your vet will review a history, perform a physical exam, and possibly advise some tests or treatment. Likely tests could include a fecal exam to check for whipworms, bloodwork, and possible xrays to evaluate her abdomen. Please have her evaluated to rule out whipworms or a possible reaction to the heartworm treatment. I hope she has a speedy recovery.

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