Immiticide Shortage

veterinary news

Immiticide (melarsomine dihydrochloride), the drug that is used to treat a heartworm infection in dogs, is no longer available.  The makers of this drug, Merial, have announced that they have completely run out of stock.  The outage may last several weeks or months.

Immiticide shortageWhat is Immiticide?

Immiticide is a powerful drug that is given by injection to dogs in order to kill an active heartworm infestation.  (It is not a drug that is used as a heartworm preventative.)  Even though this drug has many serious side effects, it is still the most effective treatment that we have to use on dogs who have heartworm.

Why is Immiticide unavailable?

Merial has not released the reason for the immiticide shortage.  All they have said is that there are “technical issues” in manufacturing the drug.

How do we treat heartworm now?

The American Heartworm Society has put out a bulletin to help veterinarians deal with this shortage.  In some parts of the world, particularly the southern US states, vets will see dogs daily who need heartworm treatment and could die without it.  This bulletin will help vets make a treatment plan for dogs who are positive for heartworm.  You can read the bulletin here, and I will summarize it below:

    • Heartworm positive dogs should be treated with steroids and possibly antihistamines and then given a heartworm preventative medication such as Heartgard.  (The reason for the steroids and antihistamines is that this medication could cause a serious allergic reaction in a dog with adult heartworms.)


    • Continue with monthly heartworm preventative medication.  This medication will not kill the adult worms, but will stop them from producing more worms.


    • Doxycycline 10mg/kg twice daily for 4 weeks, then none for 8 weeks, then repeat until Immiticide is available.  Doxycycline is an antibiotic that has some effect against heartworms, but will not kill them.  It is believed that doxycycline will make it less likely for a dog to be able to transmit heartworm to another dog via a mosquito.  (Mosquitos are the way that heartworm spreads from dog to dog.)


    •  Restrict all activity.  Any activity will put strain on the dog’s unhealthy heart and could cause serious health risks.


    • Once Immiticide is available, then start treatment immediately.


Will a dog with heartworm die without treatment?

If a dog has heartworm and receives no treatment, then yes, most heartworm positive dogs will die.  However, the treatment outlined above should tide a dog over so that they can survive and then be treated once Immiticide is available.

Are dogs in shelters dying?

I found this news story from Fox news interesting.  This shelter takes in dogs every day who are positive for heartworm, and now they are unable to treat these dogs.  They are having to euthanize dogs because they can’t cure the heartworm infection before adopting them out, and many people do not want to adopt a dog who has heartworm.  The shelter has cut their adoption rate from $95 to $20 for heartworm positive dogs.  Here is the story:

Heartworm Prevention

If your dog is not on a heartworm preventative medication, then get some now!  These medications are inexpensive and work extremely well to prevent heartworm.  They need to be given once a month.  Your dog will need to have a heartworm test to be sure that he or she doesn’t already have heartworm before starting the medication.

Have you been affected?

If you have a dog with heartworm and have been affected by this recall, please leave us a comment and let us know how this drug shortage is affecting you.

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Dr. Marie

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18 Responses to "Immiticide Shortage"

  1. Alyssa James says:

    Thanks for this information! In all the frustration and worry that this issue has caused, it’s good to hear some calm, straightforward advice about what to do until the supply is restored.

  2. Darlene Valliant says:

    Our little foster dog was to get his 1st injection this weekend. He has already been on the doxycycline for 4 weeks and monthly preventative. Because of the shortage he can’t get treated. I wonder how many rescue groups this will affect.

  3. Heartworm Treatment Shortage - Chihuahua Forum : Chihuahua Breed Dog Forums says:

    […] medication used to treat dogs that have contracted heartworms, is currently not being produced. Immiticide Shortage – The only approved treatment for heartworm is unavailable! | Veterinary News If you are not giving your dogs a heartworm prevention treatment, now is the time to start. […]

  4. Jay Archer says:

    WRT the newest shortage of immiticide, we have identified immiticide available past the expiration date (6-9 months). We also regularly have HW+ dogs and have one now needing treatment. I fully understand that the “correct” answer to the question of using it is “No, you can’t use it because it is expired,” but if it is stored properly, is there any evidence to support using expired immiticide safely? It seems that there would be 3 possible scenarios involved with expired immiticide: 1) there is no change once the magical date is reached and it is safe to use, 2) at some point (past the expiration date) it starts loosing effectiveness at some decay rate (linear or exponential), 3) it becomes toxic (more so than normal as it is a poison).

    Is there any available information on how Merial establishes the expiration date? I am sure they have some safety margin built into the calculations allowing for uncertainty. For instance, Merial could not reasonably say that one day past the expiration date their product is BAD, as that would imply some of the product could also be bad the day before the expiration date, using normal Gaussian distribution curves. A similar argument to this, when in the Navy, we often ate food past the expiration dates, because it was established by various means including random inspections, that the food was still good some time after the manufacturer’s expiration dates.

    1. DrMarie says:

      Great Questions Jay. I don’t think anyone could ever safely answer the question about the efficacy of using expired immiticide. In legal terms, it is actually illegal according to the FDA to use a drug after its expiry date, even if it is one day post expiry! However, could there be an exception when there is no unexpired drug available and a dog needs it to save his life?

      My personal belief is that most drugs are quite effective for a long, long time past their expiry date, especially a drug that is not reconstituted. There are some exceptions though – for example, the IV anesthetic propofol is made using eggs. I could see that this could “go bad” after the expiry date. My gut instinct though is that if a product already has a long expiry date then it is probably just as good even months (or maybe years?) later.

      If I was in your situation, and I had dogs who needed heartworm treatment and I had expired immiticide I would likely offer my client treatment with expired immiticide but have them sign a waiver saying that they understood there could be risks as no one knows the efficacy of the drug once expired. I would likely only offer this for dogs who were very sick with heartworm (i.e. ones where I didn’t feel safe doing Heartgard plus doxycycline until immiticide becomes available again.) Just to cover myself I may even consider contacting the FDA to find out if I am breaking the law, or if there is some legal way to do this considering that immiticide is unvailable.

      I would also be very vigilant in following up with repeat heartworm testing in the future.

      The next issue for me then would be how to charge. Can we justify charging fully for an expired drug? Immiticide is expensive! I would likely charge for my services and not for the drug.

      This is a tough issue! I’m sorry I don’t have a direct answer for you! I’d love to hear some comments from other vets as well!

      1. Jay Archer says:

        Thanks for the reply – our vet has similar opinions as to using the expired immiticide – that if the dog was in bad enough condition, he would go for it, but we should wait given our rescue dog is healthy now. He didn’t want to put her though the treatment with the possibility the drug would not be effective. It would be a great benefit if there were some data showing how effective expired immiticide was, but for now I guess we have to wait

        1. DrMarie says:

          I see what you’re saying, but really, who would do a study like that? I hope everything works out ok!

  5. nickey says:

    Recently moved to Arkansas from the North East. Took in a stray who showed up shortly after we did. Sure enough she is heartworm positive – adult and microfilaria. The vet put our name on a list for when Immiticide is available again. He started her on doxy and pred, and she got her first dose of prevention 3 days ago. She did well. However, restricting the activity of a dog who is used to running (literally) at large is not easy.

    1. DrMarie says:

      Sorry to hear that your new dog has heartworm! I pray that immiticide becomes available soon so that you can get this treatment over with!

    2. Marlaine says:

      If you have any hints on how to keep a dog quiet and restrict their activity, please let me know. That will be our next hurdle. Ours is a 4-year old lab who’s used to rough-housing and chasing his sister. We’ll keep them separated for as long as we have to, even though they’ve always been together.

      1. DrMarie says:

        This is a toughie! I have had cases like this where I have given a mild dose of sedative long term. It’s not the ideal answer, but for some dogs it is necessary. For some dogs we have to resort to crating the dog in order to keep them quiet.

        I really hope immiticide becomes available soon!

  6. Marlaine says:

    One of my dogs was just diagnosed with heartworms. It’s in the early stages with no microfilaria in the urine or blood. He’s on doxycycline. This is crazy…can you imagine if a life saving drug for humans was unavailable? It would never have been allowed to happen.

  7. Matt says:

    My girlfriend and I fell in love with a dog at the Humane Society, but she is heartworm positive. We do not know whether to get her because we are an extremely active and would like an active dog. The vet at the Humane Society told us not to hope for Immiticide to be back any time soon.

    We don’t know what to do! The dog is so sweet, but will lay down if we try to take her on a walk. 🙁

    1. DrMarie says:

      This is a tough call. Heartworm is a nasty disease. It would be wonderful if you could adopt this girl, but I think we have to be prepared that she may not do well. Hopefully immiticide will come back soon.

  8. Misty says:

    We recently adopted a heartworm positive dog, and have been unable to find treatment here in Texas, due to his rather large size. He is a pyraneese mix, I am glad I came across your site, no one has mentioned the medication options above. Thanks so much.

    1. DrMarie says:

      You’re very welcome. I hope your boy does ok!

  9. Lauren says:

    I think it’s really suspicious that Immiticide is occasionally unavailable for a long, indeterminate amount of time. The crazy part of me wonders if this is some sort of government conspiracy to reduce the pet population or the company’s effort to make more money, as in, if you’ve waited 3 months and you’re sick with worry then they can charge any amount and people will likely pay to save their pet. Also, why, if the current manufacturer is unable to make it consistently, does another pharmaceutical company not pick it up? A previous commenter was correct in saying that if this was a medication for humans, the shortage would never be tolerated.

    What makes me even more angry about the whole thing: my dog, an otherwise healthy and active dog, was on heartworm prevention for the two years we have had him. That doesn’t even make sense to me that he’s been on continuous prevention and still get’s the disease and then there is no cure available.

    1. DrMarie says:

      I’m very sorry to hear about your dog. 🙁

      Personally, I really don’t think the immiticide shortage is any sort of conspiracy. While I don’t know exactly why there is a shortage, I don’t think there is any sort of foul play going on.

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