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April 07, 2009


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Dr. Mobley, since you stated this:

With the dramatic increase in the number of dogs who get small numbers of heartworms despite taking monthly ivermectin(Heartgard 30, etc.)

Are you recommending something other than Heartgard for your patients? Have you seen an increase in the number of dogs infected while on Interceptor?

I remember you writing on your blog previously about dogs on preventative becoming infected and I asked my vet at my dog's yearly checkup and she said she hasn't heard of that happening in my area. Is this becoming more widespread across the country?


Hello, Linda,

This problem appears to be mainly in the Mississippi valley region, south of Jackson, Missouri. The farther south you go, the worse it is. It does not appear to be a problem in other mosquito infested areas, other coastal areas, lake areas, etc.

The reason for this is unclear, though several explanations have been proposed, most notably more tropical storms in the Gulf, leading to more flooding, leading to more mosquitoes, leading to more heartworms.

It is difficult to accept this explanation when you live in the Mississippi Delta on reclaimed swampland where rice is farmed. We have always had and continue to have a jillion mosquitoes.

As to Heartgard versus Interceptor, the percentage of failure rate is about the same with all three drugs that we use: ivermectin (Heartgard-30), milbemycin oxime (Interceptor and Sentinel), and selamectin (Revolution). Other drugs and products on the market are related compounds: avermectins.

If I found a preventive that was clearly better, you can bet I would be switching everyone to it. Unfortunately, this is not the case. No new drugs in the pipeline, either.

I'm attending another seminar on this on April 21st, and will post afterward.

Thanks for reading and writing.


I'll check back to see what you learn at your seminar. I give my three dogs Heartguard. I certainly want to protect them from heartworms and would like to know the best way to do that.

Cat Products

Hi, Great site and a lot of useful information


Have 2 labs both tested positive to heartworms.
1-lab vet treated, new blood work still positive.
2- lab pulling more blood work and sending to different lab. Interceptor given first of month always.
Interceptor gives us year supplies due to dogs being treated and still contacting heartworms.
Are other people having this problem with dogs.


Dear Dr. Mobley,

I found your blog through google and was very impressed. I have a few brief questions and I'd greatly appreciate your thoughts.

Recently my wife and I found a Pit Bull mixed dog in our neighborhood. We tried like crazy to find the owners, but had no luck. We are not willing to see the dog put to sleep, and thus she is now ours. I took her to our vet yesterday and he told us she had heartworms (Spot Test) and that treatment is extremely likely to be successful (assuming class 1). I knew little about heartworms at the time, and thus asked just simple questions. I'll see him in two weeks, but after some research, I have many thoughts and few answers.

We are not wealthy by any means. She is young and has no cough nor breathing troubles after activity. Your article on the "slow kill" treatment was pretty scathing, but in this case does it at least seem reasonable? I was thinking weekly ivermectin with regular doxcycline for 6 months. My hope is that the adult heartworms' lives will shortened, the extended time span of treatment will only result in limited cardiac damage, and that embolism problems will be minimal.

Also, some vet sites mention that ivermectin based preventative products are better for dogs w/ heartworms than milbemycin products, due to the milbemycin's rapid killing of the larvae. Do you agree? Some also mention that ivermectin products are more effective on shortening adult heartworms lives. I'm confused and not sure what is true and what is just internet recklessness. Regardless of whether we treat with immiticide or try the "slow kill," it seems the dog needs to be on some preventive heartworm pill to make sure new larvae heartworms are forming.

I'm sure you're busy, but hopefully you'll have a chance to offer your assistance. Thank you

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That Heartworm disease can affect people o chemotherapy ?



Heartworm disease does not generally affect people in any way, other than how they feel about their dogs.

The heartworm larvae enter people all the time via mosquito bites, but they rarely live and leave the spot where they enter. There are rare reports of finding an adult heartworm in a person's abdominal cavity, or some other weird location.

Sometimes the migrating microscopic baby heartworm will reach the lungs, and the body forms a little knot around it. This can show up on a chest X-ray, leading to a lung biopsy to find out whether you have TB or cancer or what.

Generally speaking heartworms do not affect people.

dolores Hein

what if I miss a pill for heartworms.


Hello, Dolores,

You should give the pill as soon as you realize that you missed one. Do not stop giving the pills in a situation like this.

If the dog has had mosquito exposure during this time, then it may possibly develop heartworms. You will not be able to detect this with a blood test until at least six months after the missed pill.

So, get back on schedule, keep giving the pills, and get a blood test in six months.

Thanks for reading and writing.


To ensure that your dog is free from heartworm parasites, preventive medication should be given especially in the early months of the dog to avoid such problem on the dog’s health the same applies on the cats.Visit http://dogs-corner.blogspot.com/2009/09/dealing-with-your-dog-heartworm.html


Hi Doc!
I see you told Dolores to if one if I misses a pill for heartworms..that they should give the pill as soon as you realize that you missed one...now I was wondering once you give the missed pill to your dog..do you give him the rest of the pills counting from when you actually gave him the missed pill or do you keep counting form when you were suppose to have given him that pill..hope this makes sense :) ?!


Hello, Roberto,

You could start counting 30 days or four weeks or one month from the time that you finally remember to give the pill.

For most people (like me), if I am late giving it on the first of the month, I probably will do worse trying to do it on the seventh the next month or the fifteen the next month. I'm afraid I would just be worse about forgetting.

I recommend setting a date that's easy to remember, like the first, or when you pay the rent, or payday or something.

The medicine is really safe. Thus, if you were two weeks late one month, giving it on the fifteenth instead of the first, it would be perfectly safe to give it on the first of the next month. Two weeks apart is no problem. Two DAYS apart would be safe, as far as that goes.

Thanks for reading and writing.

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Hi all! I like the post like this. It is really interesting for me.


Hey Doc

I was giving my dogs their monthly heartworm medicine. I had already fed my 8 month old puppy, Panda, and when I was taking the heartworm out for my 2 1/2 old dog, Bear, Panda ate it! I was wondering if anything bad would happen to her after eating 2 heartworms.
Thanks for your time.


Hello, Mike,

The medicine is super safe. The active drug ingredient is present in very small amounts. While I wouldn't recommend it on a routine basis, she could probably eat a handful of monthly doses with no ill effects.

Not to worry.

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Hey doc, I use baytril as antibiotic for my pets. can you suggest me some thing on this med.


Hello, Karjat Plot,

I'm not sure I understand your question. Baytril is the trade-name for enrofloxacin, a fluoroquinolone antibiotic.

When it was first approved, the dosage was recommended to be split twice daily. This is still on the label. However, it now appears that this class of drugs is more effective when the total daily dose is given once daily.

It is important not to exceed a daily dose of 5mg/kg/day in cats, as this can cause damage to the retina in the eye, resulting in blindness.

I don't use Baytril for "every day" infections, reserving it for tougher germs. Over-use of the drug will result in resistant bacteria, and reduced usefulness of the drug.

I really cannot advise you on dosing your pets, as I have not examined them.

Thanks for reading and writing.

Surgical removal of the adult heartworms is also a treatment that may be indicated, especially in advanced cases with substantial heart involvement


This treatment is usually reserved for dogs with post-caval syndrome. This is where the worms locate themselves in the large veins returning blood to the heart, usually the posterior vena cava. This results in a very rapid deterioration of the dog's condition. Red blood cells are cut like putting them through a sieve. The liver circulation is badly disturbed. They rapidly become anemic and icteric (jaundiced). They are unresponsive (usually) to any palliative medical therapy.

Inserting a long forceps from the jugular vein in the dog's neck down to heart level allows attempts at removal of these worms. You are plucking them out blindly (you hope).

There will still be worms remaining in the heart, and in the pulmonary arteries, but (if successful) you can buy the dog some time for conventional treatment.

The procedure's success rate varies considerably between surgeons. Some do well,others have abandoned the procedure. It is certainly not without risk, but these dogs have little alternative.


What are the chances that a dog who is on a heartworm preventative and been heartworm free for 4 years (their whole life) can catch heartworms from a dog in the home who has been treated with the "fast kill" for heartworms?


Hello, Ashley,

Having the heartworm-infected dog in the home does not really raise the risk of infection for the dog on preventive medicine.

The overall level of mosquito exposure is a much greater factor. There are plenty of infected and untreated-hosts in the environment elsewhere.

Sometimes our preventive medicines are not 100% effective, but even "preventive failure" cases have had MOST of the worm infection prevented.

I really would not be a bit more worried about having the other dog in the house.

Thanks for reading and writing.


I took a small rescue dog in to foster a month ago. When I had her spayed, she had severe complications post-op, but stabilized and pulled through with IVs. The vet ran a HW test and she came up positive (and in retrospect, I have noticed some occasional coughing/gagging previously, but nothing else). The surgery has been 2 weeks ago and the dog is doing well and is happy again. I will probably opt for the immiticide/doxycycline treatment, but am very worried about being able to keep the dog quiet, as I have many animals in and around the house running around and this little dog is a terrier mix with a high excitement and activity level. What is also a grave concern, is my working very long hours and thus being gone sometimes 12 hours or more (I live alone and in the country without anyone being able to check on the dog while I'm gone), so if complications arose I most likely would not be around to catch it on time! Taking off work unfortunately is not an option since I am on a very tight budget and can't afford the loss in income (the dog's treatment is even being financed through donations). Would it be feasable to keep the dog tranquilized to keep her quiet while going through treatment (split-dose)? Is there anything else I can do to greatly reduce the chance of embolisms, so as not to have to worry myself sick for the 2 month of treatment when I'm at work?


Hello, Eva,
There is a product made by Vetriscience that is called Composure, available in liquid or chewy treats. It is a supplement, rather than a drug that really helps calm a lot of dogs. It doesn't always work wonders, but in some dogs it DOES.

Low doses of the antihistamine Benadryl are pretty harmless and make most dogs a little drowsy. In more extreme situations, tranquilizers can be used.
Sometimes we have to just keep the dog in a crate, or in a puppy play-pen.
If she is in the house, she is not nearly as likely to produce those complications of exercise as she would running outside.
I would bet that you will do fine.
Good luck.


Hi Doc,

Thank you for such an informative site. It has provided me with alot of comfort.
I rescued a pound dog 3 weeks ago, HW +. On 5/2 he began Immeticide x 2, 24 hours apart. He was originally asymptomatic, with right heart enlargement thus rated a borderline class 2.
He is approx 7 yrs old, 30 lbs, lab/basset ?????
Question: he has had approx 3 episodes of labored breathing lasting about 10 min each on different days. Took him to the Emergency vet first time and it had resolved by the time we arrived so it was chalked up as possible "pain". He has tolerated the discomfort and I have not treated.(Rimadyl was dispensed) All occurred at rest (no anxiety/activity trigger) No cough, no fever, lungs were clear, gums remained pink. It is now day 7 post treatment. He has been activity restricted to the living room area only, leash to potty only. (He refuses the crate)He eats, drinks, potty's etc. Unfortunately he has separation anxiety issues when I go to work which scares me to death. Me only household.
We had an episode this morning- same thing, upon waking. Resolved spontaneously. I am awaiting a return call from my vet.
I try not to be a "nervous nellie" ( I am an ICU RN )
I know the worms are dying and shifting, but is this something that I should expect for awhile or do you think steroids should be added-- are they added routinely? Do they act preventatively against embolism? Thanks very much for your time and for this site.
Oh, and again I have contacted my vet..and waiting.



Hello, Christine,

We now start prednisone (steroids) at time of treatment. I used to wait to start them until the dog showed signs of distress.

You and your veterinarian will just have to work together on this. Not knowing all the details, it's hard for me to advise you.

Generally speaking, I think I would be starting this dog on steroids now. You can't give Rimadyl and steroids together, though.

Steroids minimize the inflammatory reaction in the pulmonary arteries, so that they don't constrict down around the worm fragments, which would aggravate the restriction of blood flow and increase pressure. The rimadyl won't really do that.

Good luck.


Nice Information.


Hello. I rescued a HW+ dog (14 lbs pom mix) from the Dallas Animal Shelter. He was not up for adoption due to being HW+ and was schedule to be euthanized. I had heard about the shortage of HW treatment meds but also heard about the slow kill method and thought I would give it a try. He just took his last weekly dose of Heartguard. A day after, he started couching/gaging several times a day, then more frequent a few days later. Is this normal? It sounds like a asthma attach.


Hello, Cindy,

Without chest X-rays it's hard to tell if your dog's coughing problems are related to the presence of heartworms or not. Pomeranians often have trouble with weak airways, even collapse of their trachea (windpipe). This can certainly cause respiratory distress.

Until Immiticide (the heartworm treatment drug) becomes available again, we are treating these dogs by giving doxycycline for one month, as well as putting them on Heartgard. This is unlikely to kill any heartworms, but should keep them weaker, and smaller, and stop them from producing babies in the blood.

With the history you have given, I would suggest contacting your veterinarian for an exam (and probably X-rays) to see if there is heart enlargement, pulmonary artery enlargement, lung problems, or airway problems.

Thanks for reading and writing.

Remi Goldstone

I can't remember if I gave my chihuhua his heartguard. Should I risk double dosing or wait until next month?


Hello, Remi,

Give it now. The medicine only stays in the body for 24 to 36 hours. NO problem with overdosing here.

Give it.

Thanks for reading and writing.


Can i start heartguard prior to 30 days after last Trifexis? Dog just tested positive for heartworm after testing neg 6 monthss ago


Absolutely. The heartworm preventive portion of the Trifexis is long gone (out of the body in 24 to 36 hours).

The low dose of Ivermectin in Heartgard is compatible with the long-acting flea control in the Trifexis, same as Comfortis (Spinosad).

Really high doses of Ivermectin, as are sometimes used to treat demodectic mange, are NOT compatible with Spinosad.

No problem switching to the Heartgard.


Rescue on Trifexis for 2 years just found out she has had them all along Just had first of 3 shots - they want her on Heartguard - please explain Heartguard vs Trifexis and what to treat fleas if she is not on Trifexis. Vet of 2 years never tested her for heartworms


Hello, Pam,

Heartgard contains a low dose of ivermectin. The heartworm gurus now believe it is the product least likely to cause a problem in a dog who already has heartworms.

Trifexis contains spinosad for the fleas, and milbemycin oxime for the heartworms. Some dogs with microfilaria present in the blood (the microscopic baby heartworms) can have a bad reaction with the milbemycin (also used in the product Sentinel).

My experience has been that dogs already taking the product usually don't have a problem continuing it. However, yours could be that one that does.

As to fleas, you could use a topical like Vectra 3-D, or you could take Comfortis, which is spinosad alone, the same flea control that is in Trifexis (same manufacturer, also). Comfortis is compatible with Heartgard; it's just two medicines instead of a combination pill.


I have a 7 year old pit bull. My income is very low as I am on disability.My girl,Abbey was diagnosed with heart worms but I didn't have the money for the treatment.

I was on a rescue site and asked for prayer for her. A girl who had worked at a rescue shelter contacted me out of the goodness of her heart! She told me that her facility in Ms was very low funded so they consulted with a local vet who told them to use Ivermectin and they did. They had excellent results.

This is pure Ivermectin to my understanding as she said I would buy it at my local feed store. She even called that vet(she is in another state now) and told him my dog's weight, breed,etc and he told her the correct cc to give her.

I was headed to buy it today and then ran across your page and saw the articles about taking the steroids, even for the slow kill. Can this be bought as well or does it need a prescription? I do not have money. I barely get by but I love my Abbey. She will not be a problem to keep "quiet" because she has always just laid around with me. We take walks and play "rope" and things but she is and always has been kind of sedentary. I am now afraid to start the Ivermectin after reading about needing a steroid as well..plus, I haven't seen anything here about buying it in a liquid pure form as this girl informed me about. Your thoughts please?

Abbey is highly allergic to fleas! Just going out to potty, they bite her legs and make big sores so I give her Benedryl for that when it gets bad. After reading your articles, I see that this is okay to give with Ivermectin. I guess it would benefit the treatment AND her flea allergy.

She goes everywhere with me, sleeps on her blanket on my bed and is constantly by my side so I would be very alert to any symptoms.

BTW, Abbey did have pneumonia, healed very well and fast, but other than that has shown NO signs of the HWs. Thanks~Debbie


P.S. I give Abbey a tablespoon daily of diatomaceous earth food grade for overall health. It has made her coat very pretty and her eyes very bright. It did rid her of other parasites as well. I found round worms in her stool and one day a couple weeks ago, she threw up a LONG slender worm..VERY long. My son said it could have been a tape worm. Was the size of vermicelli. Could THAT have been a heart worm??


Hello, Debbie,

You can't throw up a heartworm. They live inside the blood vessels in the lungs. For them to leave the body, you would have to be coughing up blood.

Tapeworms are flat, and segmented. It's hard to say what the dog threw up. Horsehair worms are parasites of insects, and occasionally a dog will eat a cricket or something and vomit up the horsehair worm. They are quite long and thin, as you describe. Not significant to the dog's health.

"pure ivermectin" I suspect refers to the injectable product for deworming cows. There is no evidence that this will clear the dog of adult heartworms in a reliable manner. People commonly dose it at about 400 times the dose approved in Heartgard or Iverhart. It works as heartworm prevention (provided your dog isn't sensitive to those doses, like a Collie - it would kill them).

If I had this situation, I would be keeping the dog on Heartgard, or another approved ivermectin product. This should be safe, and would keep you from getting more heartworms than you already have.

You cannot buy systemic corticosteroids like prednisone without a prescription. You don't need them along with the Heartgard.

Jennifer Miranda

We took in an 11 lb Shih tzu that is heartworm positive (vet stated a light case based on blood test). She shows no signs. We are trying to decide which kill method to go with but leaning towards the slow kill with Heartguard. Vet perscribed Heartguard Plus 2x per month. In your opinion are we on the right track? Should we also give Minocyclin?


Hello, Jennifer,
The best person to advise you is the veterinarian actually seeing your dog and familiar with your case.

Minocycline given for 3 weeks will cause the heartworms to weaken and physically shrink, and be easier to kill for the next 60 days or so. It also usually stops the production of microfilariae (microscopic baby heartworms).

"Slow kill" is REALLY slow - up to 5 years before all the worms die. Risk of thromboembolism (worms blocking up an artery and damaging circulation in the lungs) is present until all the worms have died and been dissolved by the white blood cells.

This is why the American Heartworm Society no longer recommends "slow kill".

Again, every case is individual, and your veterinarian has actually seen your dog to evaluate. My comments can be of a general nature only.

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