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Heartworm treatment.

Species: Dog
Breed: Pit and Lab mix - we
Age: 2-5 years
Sam was a rescue, we believe that he is a little over two years old and a pit / lab mix. We found him one year ago with two broken legs. His back leg was put in a cast, though his front leg required complicated surgery (one plate and a few pins).

Today you would not know that Sam ever had surgery. He is very active and runs our backyard constantly, chasing one of our four cats or our other dog, a hyperactive Pug.

Two weeks ago, Sam was diagnosed with heartworms. I was told that he tested negative for having (I believe the vet said) "baby heartworms or eggs" in his bloodstream. However, he tested positive for adult heartworms. The vet suggested that based on the test he might have two adult heartworms. I do not know what test they ran, but they only took bloods and a stool sample. Since this visit he has been on antibiotics.

This brings me to my question. Is Immiticide the best treatment for Sam? I understand that this is always the recommendation; however, I also understand that there is a great risk of death if the dogs heart rate goes up while on his treatment.

I cannot keep Sam's heart rate down for two months, at least without some kind of medication. Sam is very excitable - if a car pulls in our driveway or his owners walk into the house, his tail starts going and he gets excited - even if he is crated.

What should I do?


Online vet, Dr. Marie

Dr. Marie replied:

Poor Sam has had some tough issues in his life! I'm so sorry to hear that he has heartworm.

Immiticide is definitely the best and safest treatment that we have for heartworm. Did your vet mention if they have Immiticide to use for treatment? There have been issues with shortage of the drug.

With that being said, as you know, there are some risks in using it. One of the concerns is that the dog can get something called a thromboembolic event. This means that the worms, once killed can cause a problem with obstructing blood vessels in the lungs. This risk increases with a higher heart rate. So, we believe that exercise restriction really helps reduce the risk of a thromboembolic event happening.

Did the vet mention what class the heartworm disease is? We grade heartworm on a scale of 1 to 4 depending on how much heart damage the dog has at the time of diagnosis. A thromboembolic event is much more likely if a dog has a class 3 or 4 type of heartworm.

There are other options for Sam's treatment, but they are not ideal. One is something called a "slow kill" method. The point of this method is to give a monthly preventative such as Heartgard that will kill any microfilaria (baby heartworms) that are there. However, if there are currently no microfiliaria in his blood this may not be necessary. (This can happen if all of the worms in the heart are either male or female. If you don't have both a male and a female then they are not going to reproduce.) The problem with the slow kill method though is that it does not kill the adult worms. The idea is to kill larvae to prevent more adults from forming and then just wait till the worms that are already in the heart die.

However, it can take several years for the worms in his heart to die on their own. During this time they will continue to cause problems in the heart and can even lead to heart failure.

It is much better to kill those worms in the heart now than to let them sit there for several years. But, the best way we know to do that is with Immiticide.

I understand your dilemma in having trouble keeping Sam's heart rate down, but this is how I see it: Every year a LOT of dogs are treated for heartworm and how many of them do you think get excited? Almost every dog gets excited...that's what dogs do! They love to be excited about people and their surroundings.

You may need to keep Sam in a crate for 2 months and just take him out on a leash to do his business. In my mind this is a temporary hardship that should buy him many more years of life. I'm not so worried if Sam's heart rate goes up in the cage. It's the combo of high heart rate plus running around like a crazy dog that leads to a thromboembolism.

There are some vets that will prescribe medication, if necessary to help calm him down as well.

I hope this helps and I really hope he does well!

Dr. Marie.

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Disclaimer: Although Dr. Marie is a qualified veterinarian, the information found on this site is not meant to replace the advice of your own veterinarian. and Dr. Marie do not accept any responsibility for any loss, damage, injury, death, or disease which may arise from reliance on information contained on this site. Do not use information found on this site for diagnosing or treating your pet. Anything you read here is for information only.

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Dr. MarieDr. Marie is a veterinarian who practices in a busy animal hospital in Ottawa, Ontario. She created Ask A Vet Question as a resource for good, accurate veterinary advice online. Dr. Marie treats dogs, cats, hamsters, guinea pigs, and rats. She has been a vet since 1999.

Is an online vet visit just as good as a trip to your veterinarian? No! But, many times, asking an online veterinarian a question can help save you money. While Dr. Marie can't officially diagnose your pet or prescribe medications, she can often advise you on whether a vet visit is necessary. You can also ask Dr. Marie for a second opinion on your pet's condition.