Is there a good alternative to Immiticide treatment?

Eric writes:

Thank you for all the information regarding heartworm prevention and treatment. There is a lot of misunderstanding. We are an animal welfare group who took in a dog which tested positive for heartworms. The dog has received ivermectin weekly + doxycyline daily for two weeks, paused a week, and will receive another week of doxycycline.

A few studies conclude doxycyline + ivermectin kill adult heartworm: "Results indicate that the combination of these two drugs causes adult worm death." There is also internet talk of a "slow kill" method.

Do you have any advice for animal welfare groups or others with a budget that would not involve Immiticide? There are also such frequent shortages of Immiticide, it appears to be an annual event. Thank you.

For some reason, my reply is not posting to the original blog thread, so I am publishing it here.

Hello, Eric,

The American Heartworm Society has withdrawn its endorsement of so-called "slow kill" or "soft kill".

First, while some of the worms may die with long-term (like two years)administration of ivermectin and doxycycline, you cannot be certain of clearing the dog.

Second, the dog's problems with treatment arise from dealing with the death and movement of the worms within the pulmonary arteries.  We want to keep the dog's activity restricted until the dead worms have been dissolved by the body's defenders.

It takes at least five weeks for the dead worms to be cleared from the circulation.  With the Immiticide, we know when the worms will be dying (within a week), and can watch the dog accordingly. 

If you are treating long term with other medications, you would have to keep the dog's activity restricted for years, as you have no idea when (or if) the worms will be dying and moving.

The frustration with Immiticide shortage and expense is something I feel pretty personally.  While I have an adequate supply at present, I had none for several months.

My experience with humane organizations has been that resources are limited and must be allocated where they can do the most good.

When there was no indication that Immiticide would be available, the American Heartworm Society recommended monthly ivermecin (Heartgard, Iverhart, etc.) and 10 mg/kg of doxycycline twice daily for one month.  The doxy inhibits the Wohlbachia (beneficial symbiote of the heartworm)for an additional two months after giving it for one month.  Thus, they recommended repeating this at 3-month intervals.

If I were in a shelter environment, I would follow that protocol.  This is what one would do in the month prior to starting Immiticide treatment anyway.

The adopting owner just has to realize that he/she is taking on a bigger commitment when adopting a pet with heartworms.  There isn't a quick fix.

Thanks for reading and writing.

11 thoughts on “Is there a good alternative to Immiticide treatment?

  1. Susan says:

    This is a very informative article. This shortage is unbelievable but at least they’re working on more alternatives (Trying to be positive)*. I have heard that now there is a product that both kills and prevents heart worms called HWF (Heart Worm Free)- this seems to be doing the best as a substitute for right now.

  2. Doc says:

    This product has no proven effectiveness.

    I have spoken with veterinarians who are well-known experts on holistic and alternative medicines, as well as those interested in Chinese traditional herbal medicines.

    The product is considered to be what used to be known as “snake oil”, i.e. bogus.

  3. Eric says:

    Thank you Dr. Mobley.

    This dog is also not neutered and the veterinarian does not want to neuter until the dog is free of heartworms.

    We have been treating for doxycycline + ivermectin for 3 weeks so time to make a decision. I am going to the vet on Saturday and will discuss it.

    I thought this study stated ivermectin + doxycycline killed 78.3% of adult heartworms after 36 weeks, but it states “reduction of adult heartworms” so perhaps they are referring to physical size reduction, not reduction in actual number.

    Thank you for a good discussion of an important issue.

  4. Doc says:

    Hello again, Eric,

    I am not a heartworm researcher, but do try to relay correct and current information from experts I respect.

    We pre-treat dogs with this regimen, as I said before, and they still have the heartworms. It is a good thing to do, but I certainly would not depend on it clearing the dog of adult heartworms (without the Immiticide).

    Thanks for reading and writing.

  5. Erich says:

    We ultimately treated with Immiticide and the dog has now tested free of heartworms.

    At least, free based on the SNAP 4 DX.

    It was a long and hard ordeal for the dog and with all the confusing information about heartworm and prevention and treatment it seems impossible to know the best choice. The person who was fostering him is a nurse and she told me more than once she thought he was going do die during recovery.

  6. Lisa says:

    I live in an urban area of SE Michigan. I adopted a healthy young (about one year old) #80 dog that initially tested negative for heartworm (December), and placed her on monthly ivermectin. Nine months later, she tested positive for heartworm antigen x 2 different test types, no microfilaria. She had no symptoms of disease. The vet was very hostile to the idea of treating her with Doxycycline 20mg/kg/day in divided doses for one month, and continuing monthly ivermectin preventative. The vet recommended Doxy, prednisone, imiticide, overnight observation for at least two nights, lab tests, and chest x-ray at an estimated minimum cost of $1300. I elected to continue ivermectin and a month of doxycycline. My dog has tested negative for heartworm, two and a half months after completing treatment. We did not crate her, but she was confined to the house and a small area of the yard. A lot of things went into my decision to treat with doxy/ivermectin including having a large dog, a young dog, an asymptomatic dog, a dog who likely had a low worm burden, and a price tag of $100 versus $1300. There have been several studies that have looked at treating heartworm with doxy and ivermectin. While I am aware of concerns with heartworm death causing inflammatory and obstructive complications, (I had a dog die from renal failure after treatment for heartworm twenty-five years ago, not originally my dog, but a stray I picked up off the streets of Detroit) and with concerns about developing resistance to ivermectin and/or doxycycline, I do believe this is a reasonable alternative treatment for selected dogs. Please comment on why veterinarians are not willing to even consider this as an alternative treatment option.

    • Laurie Campbell says:

      You rock, my fellow Michigander!
      There are some new studies with Advantage Multi or proheart (moxidectin) that are very exciting…published and peer reviewed.
      I have two + dogs and was fortunate to encounter a great vet in Arkansas who uses moxidectin,
      when rescuing them.
      Neither of these two will undergo treatment with melarsomine.
      The science contradicts the old traditional treatments but in Michigan the vets are not keeping up!

  7. Doc says:

    Hello, Lisa,

    “Please comment on why veterinarians are not willing to even consider this as an alternative treatment option.”

    Because it doesn’t work. It doesn’t kill the adult heartworms. You affect them temporarily, so that there is less antigen (the protein from the female heartworm reproductive tract, which is what the antigen test detects, versus actually seeing the microfilariae/babies in the blood) in the bloodstream and the test shows negative. The worms are still there. You haven’t killed them.

    They are weaker, they will be smaller and easier to kill, but the effect only lasts about 3 to 4 months.

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