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Why are my dog's muscles hard and sore after heartworm treatment?

Updated on September 23rd, 2025

Pet's info: Dog | Mixed Breed Medium (23 - 60lb) | Female | spayed | 2 years old | 26 lbs

My dog was treated for heart worm infection with Diroban, with her final injections 5 weeks ago. Her bilateral sartorial muscles were very inflamed at the time and remain hard and seem tender to the touch. Is this a known side effect and is there anything to be done for her?

1 Answer

Most Helpful Answer

Jenny, DVM

Answered By Jenny, DVM

Veterinarian

Published on January 28th, 2018

Injection site reaction is common after these injections as they are given deep in the musculature. If there was any movement or any residue that got outside of the injection, then the reaction seems to be worse. At 5 weeks, it should not be painful anymore, although a firm swelling is likely to still remain. I would contact your vet for a recheck to make sure there is no infection at the site and nothing else causing a problem
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