Heartworm Treatment Drug Shortage Update

You may recall that I posted some time ago on the shortage of Immiticide, the only drug approved to treat dogs for heartworms disease (that is, to kill the adult heartworms).  They were going to have it all fixed by the end of March.

Well, now, last week it was after "March 31st", which was when I had
been told previously the shortage would be resolved. I called Merial,
and the first layer of staff said, "Not yet; they said late March or
early April." The "early April" was new to me. I asked to speak to
someone who actually knows what's going on, and she bumped me up to the
next tier in the hierarchy.

That person gave me the same story.
I said, "Look, I've been a good boy, and I haven't pretended my
patients have clinical signs when they don't. I haven't tried to order
product for dogs that are apparent lack of efficacy cases. I do have 12
people breathing down my neck wanting their dogs treated. It would help
if I could just get a straight answer for them on what the problem
actually is. Did you try to move the factory to Pakistan and the
Taliban took it over, or what?"

I still didn't get a straight
answer, but she asked how many dogs I had and what they weighed, and
sold me enough Immiticide to treat them.

Of course, I've got four
new dogs to treat since then that weren't on the original list.

If we
can get every detail of Tiger Woods' indiscretions, can't we find out
what is actually going on at Merial? And where is Osama bin Laden?
Does HE have the Immiticide?

Well, here's the news from Veterinary Information Network today… finally:

Merial Statement on availability of IMMITICIDE® (melarsomine

Recently, Merial informed veterinarians that our
heartworm treatment product, IMMITICIDE® (melarsomine dihydrochloride),
was in limited supply because the active ingredient was no longer
available from its manufacturer—the only US source of the compound.

has now identified an alternative supplier for melarsomine—one that
already produces it for the European and international markets. However,
gaining US regulatory approval for the new manufacturer will take time.
In the meanwhile, Merial has instituted a temporary measure to extend
the supply of IMMITICIDE and continue to make it available to

Through a restricted distribution program
initiated in agreement with the FDA’s Center for Veterinary Medicine
(CVM), veterinarians who have an immediate need to treat a dog with
heartworm disease will be able to purchase IMMITICIDE containing
melarsomine manufactured by the alternate supplier. This product must be
purchased directly through Merial. It will not be available through
Merial’s distributors, nor will it be available for purchase to stock
clinic inventories. Veterinarians who wish to purchase IMMITICIDE
should call Merial Technical Solutions 

Merial is continuing to work closely
with FDA-CVM and the new melarsomine supplier to gain FDA approval for
this alternate facility and return to full supply of IMMITICIDE as soon
as possible.

Not that this helps me or my patients, much.  I still don't feel like we have the full story.  They sell this stuff like gangbusters.  Why would the supplier of the raw ingredient shut down when they have a guaranteed market?  I still think Osama bin Laden may be involved somehow.

13 thoughts on “Heartworm Treatment Drug Shortage Update

  1. Sheila says:

    So now that I have just discovered I have some dogs with heavy HW microfilaria in spite of last week’S Interceptor dose and dose every month prior, NOW what do I do? Yes, snap test positive also. Wait for Osama to cough up some adulticide? When he does, and we finally treat the dogs, then how do we kill the microfilaria that are apparently resistant to Interceptor? (some of these are collies, can’t have ivermectin) This is all hugely frustrating, as I know you also are frustrated.

  2. lucy says:

    my dog has been diagnosed with heart worm and is in needs of treatment but the vet continue to tell me he can not get the med. as there is a shortage of the medication. i just lost another dog due to same condition about a month ago. i do not want to loose this one. i wonder if there is anything available that i can give my dog at the mean time.

  3. Doc says:


    Merial does have a limited supply of the medicine, but your veterinarian has to order directly from the company and they are only selling when the dog has actual clinical signs of heartworm disease. That is, they are not selling medicine unless the dog already has outward signs of disease, such as coughing, weight loss, shortness of breath, and so forth.

    If your dog does have clinical signs, your veterinarian can probably obtain the medicine to treat him

    If the dog does NOT have clinical signs, then he should stay on his heartworm preventive medicine. The greater his activity level, the more damage is done by even a small number of heartworms. Therefore, limiting both running and strenuous play is advised. Think “calm”.

    If your dog already has clinical signs, many dogs will improve when treated with prednisone to reduce inflammation in the pulmonary arteries, and doxycycline to shrink and weaken the heartworms.

    I really cannot give you specific advice when I have not seen your dog. You need to discuss this further with your veterinarian.

    Good luck

  4. Carolyn says:

    Thank you for doing this blog! I’m really enjoying your wry, no-nonsense style — very easy on frayed nerves.

    My 100 lb, 4-or-so-year old lab (probably) mix recently got a surprise positive on his heartworm test. He has no clinical signs, bloodwork (other than the test) is within normal parameters, and rads are unremarkable. My vet recommended the 2-dose Immiticide protocol, which my dog underwent last week. He has been on strict cage rest since coming home, and has been doing fairly well given the circumstances.

    Yesterday (Sunday) he coughed up a very small amount of blood-flecked sputum, so I hustled him off to the emergency vet. He was running a slight fever and rads suggested microemboli in the lungs, but they determined he was basically stable and sent him home on pred and cipro.

    Could you please speak a little bit to the actual mechanics of blood in the lungs following adulticide treatment? I get the bit about the little worm chunks in the bloodstream (not cool), but I don’t quite understand how that translates to expellable blood in the lungs.

    Also, in your clinical experience, how common is this type of post-treatment symptom? Heartworm disease is a bit of a novelty where I live — my vets are knowledgeable about treatment options, but haven’t seen enough cases to contextualize what we’re observing.

    Thank you so much–

  5. Doc says:

    Hello, Carolyn,

    When the chunks of worm move downstream, they eventually lodge in a place small enough that they can go no further. This creates an obstruction to flow, both by the simple presence of the worm, and secondarily because the blood vessel gets inflamed and swells, narrowing it’s inner diameter.

    Usually, there is still some room for flow, but sometimes the blockage is complete. In any case, the opening in the blood vessel is greatly narrowed. This works sort of like putting your finger over the end of the water hose. There is just as much pressure coming from the pump, but the opening is so small that it really jets out the other side. The amount of flow is now smaller, but pressure and velocity of the stream is now much greater.

    Thus, the smaller vessels downstream can be damaged and leak blood into the air sacs, and so you cough up flecks of blood in the sputum. Sometimes the vessel upstream bursts from the excess pressure build-up. Then you cough up a lot of blood, because it’s a much bigger artery. Sometimes you drown and die.

    Coughing post-treatment is very common. Coughing up flecks of blood is not good, but does not guarantee a bad outcome. Treatment is anti-inflammatory doses of prednisone (or some other form of cortisone) and strict cage rest. Prednisone relieves the inflammation, opening up the blood vessel. The rest is because you want to keep the blood pressure as low as possible. No running around and getting a rapid, powerful heart-beat.

    Your prognosis is still relatively good, but the dog needs to be super quiet, in as much as that is possible, for the next week.

    Stay in touch with your veterinarian.

    Good luck.

  6. Carolyn says:

    Thanks, Dr. Mobley, The garden hose is a very helpful analogy. When it comes to drowning and dying, I vote no — so whatever it takes to minimize that risk, I will happily do.

    For what it’s worth, my dog has been on sort of the standard upper-Midwest preventative protocol — none in the winter, when this may as well be the North Pole and any mosquito in it’s right mind would die, die, die.

    Any dog of mine will now be getting year-round preventative, regardless of climate.

  7. Margaret says:

    I adopted a dog three months ago that tested HW positive. I knew I wouldn’t be able to afford the $800-$1000 for treatment, but I also knew that if I didn’t adopt her no one else would, as she is just a big old mutt. She has no outward symptoms except gagging fairly frequently, producing clear but thick fluid. Do you think the gagging is related to the HW? I had her on doxycycline for a month along with Heartgard monthly, so I’m hoping for the best, but concerned about the gagging.

  8. Doc says:

    Hello, Margaret,

    Gagging isn’t usually a sign of heartworm disease. Usually you see more of a hacking type cough. More severe cases are short of breath, have no endurance. A chest X-ray will tell you more about the state of the heartworm disease than anything else. You can see if there is heart enlargement or pulmonary artery disease (which comes first).

    Your veterinarian needs to be able to see whether this is a “gagging cough”, or gagging like “I need to throw up”.

    If you have a cough that is caused by pulmonary artery disease, a round of prednisone can really help sometimes. It calms the inflammation in the pulmonary arteries, opening them up for better blood flow.

    The dog needs a good exam related to this gagging situation.

    Good luck.

    • Doc says:

      Hello, Ronna,
      We are again experiencing difficulties in getting melarsomine (Immiticide, Diroban), the drug used to treat dogs to actually kill adult heartworms. There is no shortage of the preventive medicines. The last time this happened, there was no pandemic and no war in Europe. I don’t know what the trouble is, but the stuff is back-ordered and a limited amount is available on allocation. They want us to send them the dog’s medical history before they will sell us a dose.

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