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April 17, 2008


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Brian Gardner

Are there any dietary supplements which will help strengthen the dog when this disease is diagnosed? Will such treatment help at all?


The field of nutritional supplementation has a lot of gray areas. Certainly if a dog is not in good physical condition, it will be more difficult for him to withstand the disease, as well as the stress of treatment.

Dogs eating a well-balanced diet, who look and act healthy, probably do not need additional supplementation. There are many nutritional supplements on the market, and I do not believe that any of them are magical. There are certainly good ones available, and there are certainly dogs that benefit from them.

That said, I am not aware of a specific nutrient or supplement that would support the dog through a thrombo-embolic crisis.

On the human side, we are suckers for virtually any type of nutritional supplement because we know that (as a nation) most of us eat lousy diets. Modern, name-brand, commercial dog foods provide good, well-balanced nutrition for most dogs that do not have some medical problem.

Thanks for reading and writing.


In the last few months, I have had 4 of my dogs test positive for HW, in spite of absolutely monthly year-round doses of Interceptor. 2 are large breed dogs, one is a beagle that has been mine since she was a puppy in 1999, one is a 25 pound mixed breed dog I received as an adult about 5 years ago. All of these dogs were negative at their last test. Two of them live outside, 2 of them live inside. In addition to the HW problem, we also have difficulties ridding them of whipworms, which the Interceptor package insert say it will handle adult whips. If you find a safe, effective alternative preventive, please blog about it, we would love to know.


I wish that I had an answer for you. To the best of my knowledge,there are no new drugs in the pipeline. I was giving my own dog Heartgard on the first, and Revolution on the 15th, (i.e. dosing twice monthly)and she has heartworms this year.

While I have had generally good luck with the Interceptor for whipworms, I'd probably use Panacur monthly for 3 months in the dogs that have this problem. Knowing that you generally have a fairly sizable dog population, it is possible that there is a heavy re-exposure rate from fecal contamination of the soil.

Thanks for reading and writing.


When I lived in Florida I had a dog come up positive for heartworm when he had never missed a dose of Frontline Plus in his entire life.

I had six dogs at that time and he was the only one to come up positive. I know none of the other dogs ate his dose because I administer them personally.

Now that I live in New England again, my fear of hearworms has lessened, but I'm still afraid one of my dogs will get them even though they get heartworm preventative.

He was treated successfully and is a very healthy dog.


oops - that should have read -- Heartguard Plus, not Frontline... Duh!

Bettina Hart

I have 3 dogs who have been on Heartgard Plus their entire lives; never missed a dose. My large breed, mainly outdoor dog was just diagnosed with a positive heartworm (antigen test). He starts treatment Tuesday.He's very active, barking and jumping, and I'm very concerned about keeping him quiet to avoid PTE. I live in Northwest Alabama. People should be told that the preventive is NOT 100% effective and should get their dogs tested twice a year. Thanks for your website-


Hello, Bettina,

I guess nothing is 100%, but I really felt that our
heartworm preventive were nearly that until 2006.
This has been an almost daily source of disappointment
for me in the last two years. I really appreciate the
companies standing behind their guarantee, but it's
still not fun.

Thanks for reading and writing.


I thought Ivermectin was a treatment, not a preventative? It will kills worm larvae if they're there, but it doesn't stop them from appearing at all.


In other words, even if a dog gets some worm larvae while between doses, as long as he gets the next dose he's due for on time, he should be just fine. Since the drug doesn't -prevent- worms, of course they're going to appear once in a while. But the drugs will shut them down pretty fast before they even start to hurt the dog. It seems like not that big of a problem, it's just the drug working the way it always has...


Ivermectin is considered a "heartworm preventive drug" in that it is supposed to prevent the development of adult heartworms.

Mosquitoes infect the dog with microscopic larvae daily and it takes these larvae at least six months to mature into adult worms in the heart.

When one gives the ivermectin each month, he is (it is to be hoped) killing all the heartworm larvae that the mosquito has brought there in the previous few weeks.

The apparent change in my geographic area is this: there is a significant increase (tenfold) in the number of dogs who develop adult heartworms, despite regular monthly doses of ivermectin and other heartworm preventive drugs (selamectin, milbemycin oxime, etc.). If the ivermectin were killing all the developing larvae, this would not be happening.

Amy Walker

I have a 5yr old german shepherd that has just been diagnosed AGAIN with heartworms. Two years ago he tested positive after being on Interceptor since he was a puppy. I was shocked and so was the vet! He was treated and switched to Heartgard Plus. We live in Louisiana, so mosquitos are prevalent; but the cases of heartworms in dogs treated with preventatives still appears to be fairly unheard of. My concern is that 2 preventative medicines have not worked, so what do we do now for prevention once he is treated? I am not so confident that any of them are going to work for a long period of time. I will still give my dog the preventative medicine recommended by my vet, but I'll just be waiting for the eventual bad news of a re-occurance


Hello, Amy,

I am surprised that your veterinarian has not had previous problems.

Here is a link to a series of articles describing the problem in the Mississippi valley over the last 3&1/2 years.


I recently attended a seminar given by Dr. Blagburn of Auburn University who believes that a resistant strain of heartworm may be developing.

We have had a lot of cases like yours: owner conscientious, giving the meds, dog shows a positive heartworm test. The good thing is that these dogs have very few worms, so they almost all do fine with the treatment. The preventive IS working, just not 100%. The other good thing is that the companies have been very good about honoring their guarantee and paying for the treatment cost.

Do NOT stop giving the preventive, DO get the dog treated. Repeated treatment does not appear to be harming the dogs (I have one patient who has been treated five times, and YES, he has taken 3 different preventive drugs, and NO, he hasn't been positive every year, just a lot of years.).

Feel free to write if you have further questions.

Cathy Wells

I have a two year old min pin that has had Ivermectin poisoning from HeartGuard. Out vet has been treating her for at least four months. She seems to get better and then backslides. At times we have to force feed her and then she will start eating. She was doing better until she started coming in heat and now she won't eat again. She's really losing weight and I'm really worried. Any ideas on something she might eat? We have tried everything we can think of. Any suggestions would be appreciated.

Cathy in Texas


Hello, Cathy,

Obviously, I don't know the details and have not seen your dog. Therefore it is not appropriate for me to second-guess your veterinarian.

On the other hand, that does sound bizarre. Ivermectin toxicity is seldom seen in breeds outside the herding group (Collies, Border Collies, Shetland Sheepdogs, Australian Shepherds, Australian Cattle Dogs, etc.). When it is seen there, it generally causes neurological signs.

Dogs with a very large number of microfilariae (baby heartworms) can suffer a reaction if those tiny parasites all die at once when given ivermectin.

The four months of illness is dramatically different from that.

How much Heartgard did your dog eat? It is not uncommon to give the equivalent of 400 Heartgard doses at once when treating Demodectic mange with ivermectin.

Even if my original diagnostic tests suggested the ivermectin to be the dog's problem, after 4 months, I'd be backing up a little. Sometimes you have to really start over again, pretend you don't know anything about what has happened and take a fresh look. Re-do the blood tests and so forth. At that point, I'd be calling a specialist to help me review the case.

If your doctor has suggested repeating some of the diagnostic tests, I'd sure be inclined to let him do that.

Good luck.

Bettina Hart

Hi Doc. I wrote you in 2008 when my 6 year old border collie mix was diagnosed with Heartworms, even after being given his Heartgard year round. He survived treatment and had two negative tests in 2009. Yesterday he tested positive, not just on the antigen test, but for microfilaria. The vet performed 3 diferent tests twice, with two different samples.I am sick that he has to undergo treatment again, especially since he is showing some liver problems. I dose him religiously, he chews his Heartgard, doesn't vomit.I even increased his dose to 340mcg instead of 272mcg (he's 90 pounds.) SOMEONE nedds to investigate this Heartgard failure! I have read with interest the articles re preventive failure in the Miss. Delta and the latest Heartworm Symposium in Memphis. What do I use for a preventive if he survives this treatment? Thank you for your website and blog.
Bettina in Northwest Alabama


Hello, Bettina,

I feel your pain. I have had dogs come up positive and do fine on the same preventive the next two years, then come up positive again. I have had dogs come up positive after being cleared for several years in a row.

I have tried changing preventives, giving two different preventives per month (every two weeks), increasing doses, and still had some failures.

There are people who believe that Advantage Multi might work better, IF the problem is a more rapid maturing of the heartworm larvae. This has not been proven.

I have seen fewer failures in 2009 and 2010 than in 2006,07 and 08. I'm still seeing them though.

Your dog will probably tolerate the Immiticide again, even with the liver trouble.

People ARE investigating this now, rather than stonewalling like they were 3 years ago.

Good luck.

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