Thursday, September 1, 2011

The "Slow Kill" Method of Treatment

---> Immiticide Unavailability<--- 

Pedigree Foundation Write a Post, Help a Dog (this is to help shelter dogs get a donation of dog food)

Back in the day, when Immiticide was available, people would talk about slow kill vs. fast kill. Right now, slow kill is all that we have but hopefully eventually (soon eventually, not eventually like putting a person on Mars eventually) we will once again be able to look at the decision between the two methods.
This is from an article by By : There are a lot of misconceptions about heartworm treatment in dogs. One of the most common misconceptions is that using ivermectin-based heartworm preventive medications for a "slow kill" is the preferred way to treat canine heartworm disease.
People think slow kill is preferred. But it's not. As our 9th grade Spanish teacher used to say, "Repita, por favor." Slow kill is not the recommended method of treating heartworm disease.

Obviously, the American Heartworm Society has its recommendation, that we follow, of doing the fast kill with one injection, a month of cool inactivity, and then two more injections a day apart, and another month of cool inactivity.

We do typically give the dog Ivermectin based heartworm meds under the direction of a veterinarian for a few months prior to starting the fast kill though.

But this quote from information at Dog Aware is something that needs to be stressed - the only choice we do not have is not to treat.
Whether you elect to do the fast-kill method using Immiticide, or the slow-kill method using monthly Heartgard, either is preferable to leaving the dog untreated, or using unproven, alternative methods that may have no effect or even be harmful. 
If someone is not able to work out payment plans at their vets, tries some of the great fundraising ideas on this website: and doesn't get anywhere, or if the health of their dog, as determined in consultation with their vet, could not handle the recommended method (1 shot 1 month, 2 shots the following month 1 day apart with 2 months of cool inactivity) then it is much better to do something to treat, then nothing at all. Without a doubt.

What is slow kill?
Monthly administration of ivermectin-based heartworm preventive medications alone are sometimes used as a second method of heartworm treatment. This is referred to as the "slow kill" or "soft kill" method.
How long does it take?

Slow kill can take 18-24 months. Yowza. That's a long time for a dog to be inactive. Oh, yes, the dog needs to be inactive during that time. Quiet in the house, crated if they can't be quiet, and leash walked for potties only. You know why. Yes, clots. (cha-ching - where is my clot reimbursement check? what? clots don't have money? there goes my blog paycheck!) Why else? Because the more active the dog, the sicker they get. Even if they have less worms. That's in the immiticide unavailability link at the top of this post if you need to review.

What happens to the dog in those 18-24 months?
From Dog Aware again: Although heartworm treatment can be dangerous, so are the heartworms themselves. Adult heartworms are large, growing up to 12 inches in length and living as long as five years. They can plug up the pulmonary arteries, and when the infestation becomes severe, they will start to back up into the heart and eventually fill it. They can cause blood clots, and force the heart to work abnormally hard to pump blood through the clogged arteries. In addition, heartworms cause an extreme inflammatory response in the arteries that can affect other parts of the body, especially the kidneys and liver.
So basically damage to their heart, lungs, liver and kidneys. That's never good.

What are the disadvantages of the slow kill method?

Bottom line, only Immiticide kills the adult worms, and the adult worms are the ones that do the big damage.
From the AHS on
  • The adult heartworm is responsible for the damage to heart and lungs that causes the symptoms of heartworm disease in dogs.
  • Melarsomine (alias Immiticide) is the only medication we have available that can kill these adult worms. Ivermectin kills the larval stages but not the adult worms. It also does not shorten their lifespan or render them sterile.
  • With time, as long the larval stages do not survive and no new infections occur, the adult heartworms will die of "natural causes." However, this may take as long as two years to occur.
  • As long as there are adult heartworms living in the heart and pulmonary arteries, the damage to these organs will continue. That means that while your dog is receiving only the monthly ivermectin medication, his heartworm disease will continue to progress and his heart and lungs can suffer severe damage.
  • Another reason that monthly ivermectin treatment is not recommended for heartworm-infected dogs is that some parasitologists believe that the "slow kill" method has contributed to the development of strains of heartworms that are resistant to heartworm preventive medications. (Dr. Byron Blagburn, webinar, Emerging Issues in Heartworm Prevention, presented by DVM360, 4/20/2011)
Another list from the VIN about what Ivermectin based meds do and do not do:
Ivermectin Only
This option has led to a great deal of misconception about the ability of ivermectin to kill adult heartworms. Let us lay the rumors to rest now:
  • Ivermectin does not kill adult heartworms.
  • Ivermectin does shorten the lifespan of adult heartworms.
  • Ivermectin does sterilize adult heartworms.
  • Ivermectin does kill microfilaria (keeping the dog from being a source of contagion)
  • Ivermectin does kill L3 and L4 larvae (preventing new infections).
This means that if you opt to treat a heartworm positive dog with an ivermectin-based heartworm preventive only, you can expect the dog to remain heartworm positive for as long as two years and the heartworm disease will be progressing during those two years. This is not good for the dog but certainly beats getting no treatment of any kind.
BUT, big giant but, if you and your vets determine it is safest and best to do slow kill then that you and your vet do what is best for your dog. This blog is just information from other sites, collecting and explaining their recommendations in words we can understand better, but it is not a substitute for individualized treatment plans, which is why we always say, talk to your vet. You now have a lot of information about the two most common types of treatment so that you can talk to your vet about both and know why the AHS and veterinary college hospitals all recommend the 3 injection fast kill method. 

You'll probably notice that we keep saying Ivermectin based medicine (one example is Heartgard). We are not saying straight Ivermectin. We know that everyone knows someone who uses straight Ivermectin that they get from the farm supply, but that's not what we are referring to. We are talking about the meds you get from your vet and talk to your vet about.

We are also not referring to other heartworm medicines. Here's some good information as to why - some just aren't that into heartworms:

And here - oh my: If Interceptor (milbemycin oxime) at normal doses, or Heartgard at high doses, is used to kill microfilariae following heartworm treatment, anaphylactic shock can occur, especially in dogs with high microfilariae counts.

This website: nice enough to explain this study: which talks about adding Doxycycline to the Ivermectin based heartworm medicine. That is also recommended in the link at the top of the page.

Once again, the one thing we can not do - is nothing. While fast kill is generally the recommended method, if it is a choice between slow kill and nothing at all - your dog will benefit from treatment under a vet's supervision. 

Next: Mila's second treatment


  1. I have been treating my 80 lb Chocolate Lab with a slow kill treatment of Heartgard. My vet told me since she was such an active girl that the slow kill would be best for her. Initially, I dosed her with Doxycycline for 30 days with the Heartgard that my Vet advised. It has been two years since she was diagnosed HW+. At this point my question is, is it safe to give her liquid Ivomec?

  2. My doc to suggested the slow kill method for the Heartgard treatment, but then my uncle told me about revolution dogs from CanadaVetCare. I decided to buy this treatment for my pet dog & it did worked. It was like magic for me. I definitely recommend this to you as well.

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