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Why the 30-day wait for melarsomine after my dog's heartworm meds?

Updated On September 23rd, 2025

Pet's info: Dog | Mixed Breed Medium (23 - 60lb) | Female | spayed | 1 year and 8 months old

My dog just completed a first round of Prednisone and doxycycline for heartworms. Im wondering why we have to wait 30 days until they can give her the first melarsomine shots. She's handled the doxycycline &prednisone like a champ, is still very healthy and if I allowed her to would continue with her rigorous daily exercise routine. Aren't the adults still in there growing &negatively affecting her heart and lungs? When last I asked our vet she said it was protocol. And no other details.

1 Answer

Most Helpful Answer

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Answered By Dr. Leigh, DVM

Veterinarian

Published on February 16th, 2017

The Melarsomine is not effective against juveniles under 4 months of age. It is recommended to administer a heart worm preventive for 2 months prior to administering melarsomine. This will decrease new infections, eliminate existing larvae, and will let older worms (between 2 and 4 months of age) mature so they would be more susceptible to melarsomine. Below is a link with a chart for the recommended schedule for treatment. https://heartwormsociety.org/images/pdf/Canine-Guidelines-Summary.pdf

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