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April 09, 2010


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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.



The American Heartworm Society's official recommendation is to restrict the dog's activity as much as possible. This is because there is a direct relationship between the intensity of the dog's activity level and the degree of damage produced in the pulmonary arteries.

Ah, but for how long? Until we get more Immiticide and finish the treatmetn regimen, apparently. That's a little tough.

We are having some luck killing out microfilariae by giving doxycycline for about four weeks. This kills (or inhibits or something) Wohlbachia, the symbiotic organism that helps heartworms thrive. We have had some patients who after Immiticide treatment were negative for adult HW antigen, but had persistent microfilariae in the blood. These would not clear with repeated high doses of ivermectin or doramectin (which you wouldn't do in Collies anyhow). Some of these have cleared with the doxycycline treatment.

The heartworm society recommends treating dogs that are clinically ill with anti-inflammatory doses of corticosteroids. This relieves the pulmonary arteritis, opening the lumen of the vessel, and reducing resistance to flow. Many times this will give remission of clinical signs for several weeks. Of course these dogs are also recommended for the restricted activity guideline, as well.

If you have a dog with clinical signs, your veterinarian can probably obtain Immiticide to treat him.


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.



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


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--


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.


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.

Acai Berry Pure

I totally agree with you... so far so good, you have one of the most educative posts,. I'll rate you 80 % of my personal rating... keep the good work


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.


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.

Victoria @ Three Wheel Bike

Is heartworm treatment and phenobarbital ok to take together with dogs?


Hello, Victoria,

There should be no problem with this.

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