Heartworm Treatment for Dogs: What You Need to Know

Dog at vet

Odds are, you've visited at least one veterinary office that prominently displayed a photo or drawing of a canine heart infested with heartworms. This gruesome image illustrates what can happen to your dog when the spaghetti-like worms clog his heart.

As a dog owner, you're probably aware of the risks of heartworm disease, and I hope you are taking precautions to prevent it. But beyond gawking in horror at the poster in the vet's examining room, have you ever thought about what’s involved in treating heartworm? Believe me, it’s not a simple matter for your dog or for you.

Step One: Pre-Adult Heartworm Treatment

Once your dog is diagnosed with heartworm disease, your veterinarian may recommend a course of antibiotics, heartworm preventives and steroids before beginning the actual adult worm treatment.

Antibiotics may be prescribed because a bacterium found living inside the heartworms — Wolbachia — is thought to contribute to an inflammatory response within the body. When the heartworms die, they release the bacteria into the dog’s body. Researchers believe the presence of Wolbachia may cause the body to mount an immune response that could worsen not only the heartworm disease but also the lung and kidney inflammation seen in dogs with this condition.

For this reason, many veterinarians begin treatment by prescribing doxycycline, based on promising results from published studies of doxycycline use in dogs infected with heartworms.

Since the heartworm treatment only kills adult worms, veterinarians may prescribe a monthly heartworm preventive to kill the smaller larvae before initiating adult heartworm treatment.

The administration of corticosteroids at the same time as the antibiotics and heartworm preventive also helps reduce inflammation.

Step Two: Treating the Disease

Once your dog has completed the course of steroids, heartworm preventive and antibiotics, he should be ready to start the actual adult heartworm treatment. The treatment for heartworm disease takes at least 60 days to complete and consists of a series of drug injections that kills the worms. There is only one drug approved by the Food and Drug Administration to kill adult heartworms in dogs, an organic arsenical compound that is injected into the dog's lumbar, or back, muscles.

On the days injections are given, your dog must stay in the hospital for observation to make sure he doesn’t have any serious reactions to the treatment. Your veterinarian may also prescribe a tapering dose of steroids for a period of time following the injections.

But, wait, there’s more! Your dog should be retested after treatment and six months later to ensure that all of the larvae, microfilariae and adult worms are dead. Dogs who remain heartworm positive six months after treatment may need to repeat treatment to kill the remaining worms.