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Tuesday, August 16, 2011

Heartworm Treatment Crisis

When we treat heartworm disease there is really only one medication that most vets reach for, called Immiticide (melarsomine).  It first came out in the mid-1990s, replacing the previous drug of choice, Caparsolate.  The latter drug isn't used by most vets anymore because it runs a higher risk of side-effects and can cause significant tissue damage if it gets outside of the vein.  Immiticide is much safer and less irritating, making it the gold standard for around 15 years.

For the last two years Immiticide has been in short supply because of ingredient shortages and other manufacturing problems.  Currently it is only manufactured by one pharmaceutical company, Merial, and they have limited sources of the ingredient.  For the last two years when we wanted to treat a pet we had to directly contact the company, discuss the case, and get them to ship it directly rather than ordering it through typical distributing systems.  This method allowed Merial to keep the supply going to pets that really needed it rather than sitting unused on vets' shelves.  It was a real hassle to us vets, but I never ran into a problem getting it when I needed it.

That is changing.  A couple of weeks ago Merial announced further problems to the point of them not being able to produce any more Immiticide for the foreseeable future. The only product left is what is sitting on shelves in offices and warehouses, and that will quickly be depleted.  Merial is hoping to have more available within seven months, but there is no promise this is the case.  So treatment is now being withheld from mild cases without symptoms and being reserved only for severe cases.

This is extremely frustrating, and keeps us from providing the best care for pets.  I also think it's crazy that we are so dependent on one single source for such an important medication, leading to situations like we currently have.  Honestly I don't know all of the details behind Merial's problems, but with a shortage being known for about two years I would have hoped that someone would have come up with alternative sources by now.

This means that many people who have their dogs diagnosed with heartworms will have to go without proper treatment, instead relying on symptomatic control and other secondary treatments that aren't as fast or effective.  However, keep in mind that this is a completely preventable disease!  There is no reason for dogs NOT to be on heartworm prevention.  So a solution is pretty simple from one aspect...use prevention and your dog's won't get the disease!

And let's hope that this shortage ends soon.


  1. I was reading about this on VIN. Very disturbing. I do a lot of rescue work and intermittently get positive dogs. Now what are we going to do with them? Can't treat em, can't adopt them out...

  2. What about ivermectin? There have been studies done that show 80% of HW positive dogs show no signs of infection after a regime of the appropriate sized heartworm medication every two weeks for 6 months.

  3. Anonymous, I haven't heard of that study and would be interested if you had a link or source. I've actually seen data, backed up by my personal observations, of dogs who are on ivermectin therapy for years and are still positive. Most heartworm preventions are ivermectin-based and don't function as effective adulticides. They may shorten the lifespan of the heartworms, but that still leaves the worms living for around 4-5 years, causing damage the whole time.

    The closest study that I've seen was published within the last year and showed dogs who were on a combination of doxycycline and ivermectin prevention. Most of them were negative for heartworms after a year of therapy. The problem is that this was one study that hasn't been verified and it was on a small sample size. While I've considered it seriously myself and will likely look more at it, there just isn't a lot of data.

    Immiticide is still the most widely used, safest, and most certain method of treating heartworm disease.

  4. There is still the slow kill method. the vet clinic I work for ion my home town has used it for a while. We use heartworm prevention with doxycycline added to it to slowly kill the heart worms. The DR i work for his just recently went to a continuing education class and they said to use the slow kill method (hwp) and add doxycycline for 30 days skip 60 days then add it back for 30 days and so on until you get a negative reding.

  5. I will see if I can find the study online. The latest study was done at University of Wisconsin, I believe. The original study was done over 10 years ago, however I am unsure where it was done. I will try to get more information to you as soon as possible.

  6. The main problem with the slow kill method that I've seen and worried about is that you don't know when the worms are going to die. With Immiticide you have a small and predictable window in which the adult worms will die, and you can anticipate potential reactions during this time. When you're slowly killing worms over 1-2 years, you don't know when they're going to die. So rather than 2 months of worrying about pulmonary emboli, you have 12+ months. Not the best odds, in my opinion.

    However, I'm certainly looking at other options, and have been looking at studies that show how doxycycline can help kill worms faster. This is still a developing situation, and we only discovered the effectiveness of doxycycline within the last few years. There are still many unanswered questions.


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