Tips and Methods for Preventing Resistant Heartworm in Dogs

Updated on July 18, 2019
DrMark1961 profile image

Dr. Mark is a veterinarian. He works mostly with dogs and exotic animals.

Your dog should stay heartworm free and able to do everything!
Your dog should stay heartworm free and able to do everything! | Source

What Is Resistant Heartworm?

In several articles I have published here, I have recommended the purchase of generic ivermectin (for use in cattle or sheep) to use for heartworm prevention in dogs. Recent reports have shown that the Merial heartworm preventative, Heartgard, is not 100% effective in all areas. Some resistant strains of heartworm (MP3) have been reported in the southern US. One strain was found in Georgia, another in the Mississippi valley.

A meeting of the American Heartworm Society and Companion Animal Parasite Council in 2010 led to some new research by Auburn University´s College of Veterinary Medicine. They tested four commercial heartworm preventatives and found that only the Advantage Multi was 100% effective against the new strains.

Does this mean that you should stop using ivermectin to protect your dogs?

Tips for Preventing Resistant Heartworm

  1. You can give ivermectin as a heartworm preventative year round.
  2. You can give ivermectin at a higher dose.
  3. You can give ivermectin twice a month.
  4. You can continue to give ivermectin for its effectiveness against dogs infected heartworms.
  5. In some cases you should not count on ivermectin as your heartworm preventative.

Heartworm disease can strike any dog at any age.
Heartworm disease can strike any dog at any age. | Source

1. Give Ivermectin as a Heartworm Preventative Year Round.

You can give ivermectin as a heartworm preventative year round. The researchers found out that the efficacy rate for ivermectin was about 95%, but in unpublished results it was 100% effective after three consecutive doses were given. Giving heartworm preventative year round is probably effective enough to kill all of the microfilaria.

2. You Can Give Ivermectin at a Higher Dose.

You can give ivermectin at a higher dose. I will revise the dosages in my heartworm prevention article so that they will be equal to about two Heartgard chewables. This dose is still low and quite safe. A dog being treated for demodectic mange receives a higher dose for a long period of time. (You should not use comfortis flea control, however. It is another type of insecticide and it may affect your dog. Heartworm should be prevented chemically but you should get rid of fleas without chemicals.)

3. You Can Give Ivermectin Twice a Month.

Giving heartworm preventative every 15 days, instead of every month, is more effective and will kill more of the microfilaria. If your dog becomes infected with a resistant strain, this probably will not help, however.

4. Continue With Ivermectin for Its Effectiveness.

It is almost 100% effective when given continuously for 31 months—the drug can be used as a type of slow treatment; your dog is unlikely to die from having a dead mass of worms die and lodge in his lungs, a serious side-effect of the rapid-kill method. Revolution may kill some adults, but less effectively, and neither Interceptor nor Advantage are effective in killing adults.

5. In Some Cases You Shouldn't Count on Ivermectin.

If you live in the Mississippi Valley, from Missouri to Louisiana, current recommendations are that you purchase Advantage Multi from your veterinarian. This product is more expensive and I cannot guarantee that it is worth the additional expense.

Resistant heartworm disease can strike any dog.
Resistant heartworm disease can strike any dog. | Source

What Is the Best Way to Prevent Heartworm Disease?

A three year supply of ivermectin (in the sheep drench formula) given year-round and at a higher dose, is still less expensive than a six-month supply of other commercial heartworm preventatives. If you want to continue having your dog tested every year, and continue using the commercial heartworm prevention year-round, there is nothing wrong with that—it is your money and your decision.

(The only problem might be with the dewormer, pyrantel pamoate, which is present in Heartgard plus. It can make some dogs vomit if given in too high a dose.)

If you are keeping your dog on the Merial product so that the company will pay for your dog´s heartworm treatment, that is going to be little comfort to him as he feels the long needle shoved into his back, feels the cold arsenic injected deeply into his body, or is incarcerated in a cage or crate for weeks after the treatment.

The best way to protect your dog from heartworm infection is to make sure she is never bitten by a mosquito. That may be impossible, but you can lessen the risks by keeping her inside during the time when mosquitoes are heavy around your house (around here it is early morning or dusk), putting mosquito screens up on all your windows and doors, and using yellow bulbs on all of your outside light fixtures. I live in an area where several people die each month from zika and dengue so our health department comes around each week to discover and eliminate any sources of standing water—birdbaths, old tires, and bottles can all become mosquito breeding grounds. Your dog will still be at risk, so it is a good idea to keep him on a preventative, but the chances of her becoming infected are very slight.

This situation may change. I will add any updates as new material becomes available.


What is the best way to keep your dog free of heartworm disease?

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This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.

Questions & Answers


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      • profile image

        Charlene Latimer 

        2 years ago

        Thank you for this valuable info.

      • profile image

        Bob Bamberg 

        7 years ago

        I vote for piperazine and parantyl pamoate as the likely p-word dewormers in Rachel's barn.

      • DrMark1961 profile imageAUTHOR

        Dr Mark 

        7 years ago from The Atlantic Rain Forest, Brazil

        Rachel I would not even worry about it in Pennsylvania. The MP3 strain (the resistant heartworm) was found one time in Georgia and never seen again. The only time it has been seen consistently is in the Mississippi valley, from St. Louis to Louisiana. The other heartworm preventatives you could buy are expensive and will need a prescription. It may be a problem 10 or 15 years from now, but at the moment your area is fine.

      • Farmer Rachel profile image

        Rachel Koski Nielsen 

        7 years ago from Pennsylvania, now farming in Minnesota

        Hi DrMark, great hub as always. I'm concerned about the ivermectin-resistant heartworm strains. The large animal vet we used to use here at the farm recommended that we rotate dewormers for the horses, cattle and sheep every three months. I can't remember the active ingredients in the other 2 dewormers (I can go out to the barn and look if you want, both started with a "P" and were long words, lol) but I was wondering if there are other heartworm preventatives besides ivermectin that would be safe for dogs?

      • profile image

        Bob Bamberg 

        7 years ago

        I should set up a mosquito dunk kiosk on your beach! Bet I could make a few bucks. :-)

      • DrMark1961 profile imageAUTHOR

        Dr Mark 

        7 years ago from The Atlantic Rain Forest, Brazil

        I think the mosquito dunks are just overlooked. The government makes a lot of recommendations that don't help much (like making sure that you do not overwater your house plants) but I would think they would think of everything, since so many people die every month (from dengue).

        We have the generic ivermectin available here too, and the prices have fallen a lot in the last few years!

      • profile image

        Bob Bamberg 

        7 years ago

        Re: the BT mosquito dunks not being recommended where you are... are they not recommended as an unintentional oversight, or are they recommended against? I can't think of any reason why they should be prohibited, but if you guys have one, I'd really be interested in learning about it.

        I carried the Ivermectin Paste for the horse community, but never could sell any of the drench. I think there was a price aversion, although I never thought about bringing it in after the patent expired.

        When that happened, Zimecterin went from $14.99 a tube down to $9.99, and then all the other mfgrs started producing their versions of Ivermectin so now it's down to 6 or 7 bucks.

      • DrMark1961 profile imageAUTHOR

        Dr Mark 

        7 years ago from The Atlantic Rain Forest, Brazil

        Thanks for the input on the mosquito dunks. That isn't something recommended around here, although it should be since we have such a huge mosquito problem.

        The only problem with the ivermectin paste is the strength, it is 1.87%, so a lot more than the sheep drench product. Still, as you point out with the "beagle guys", there is a good margin of safety, so it is unlikely to cause problems.

        Thanks for your comments. I am glad always glad to read your interesting input!

      • profile image

        Bob Bamberg 

        7 years ago

        Good hub, Doc. I echo your economic points about Ivermectin. At my feed and grain store, we sold the paste for $7.99 a tube. The syringe is graduated for a 1,000 lb animal, so dosing is tricky but I knew of several people, especially the "beagle guys" who used it and I never heard of any problems. Of course I also don't know how effective their dosing was, either.

        But that one tube provides a large number of dosages. Even if one couldn't use it up by its expiration date, they'd still be saving money.

        Through you, may I suggest to Jaye and others who have a lot of standing water, the use of mosquito dunks. There are various brands but they all work the same way...BT (bacillus thurengiensis).

        It biologically controls mosquito larvae in standing water, but is harmless to all other life forms. You can even use it in bird baths and garden ponds without harming the birds, fish and other aquatic life in garden ponds. You'll find the product at any feed and grain, nursery or garden supply outlets.

        I believe it's meaningful that alternative methods be offered from credible sources, which is why I think your hubs are so important. Keep 'em coming! Voted up, useful and interesting. Regards, Bob

      • DrMark1961 profile imageAUTHOR

        Dr Mark 

        7 years ago from The Atlantic Rain Forest, Brazil

        I think the people in Georgia and Alabama don't have to worry much but you definitely need to be concerned. The new strain might be rare but dogs in your area definitely need the extra protection.

        Does your vet want to give your dog the Proheart injection, knowing of her other health issues? The Advantage Multi might be a better idea. (They both use moxidectin.) The Proheart injection caused a lot of health problems, and some dogs even died, so it was pulled from the market. (This was back around 2004, but I am sure you can still find plenty of info on the internet about it. Be sure to read about this before making your decision.)

      • JayeWisdom profile image

        Jaye Denman 

        7 years ago from Deep South, USA

        I'm so glad you wrote about this. I read a report about a study by a veterinary school, and the results showed only the active ingredient moxidectin (found in Advantage Plus monthly and Proheart 6-month injection) was truly reliable in the prevention of resistant heartworms. Ivermectin did not protect against them. This really concerned me because I live in an area that is heavily infested with mosquitoes. To make matters worse, there is a city drainage ditch nearby, and the city water & works department does nothing about standing water.

        My dog gets her annual heartworm test next month and her first Proheart injection afterward. No more Heartgard.



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