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August 25, 2010


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Kellie Olinsky

I have a 12-15 mouth old Bullmastiff that I just rescued with B2-Class 3 heartworm. I do trust my vet. But I was just confussed because I was told to give him interceptor 3 days after the first tx with immiticide it was one dose and then in 35 days the next 2 injections will be given, He is on prednisone.I am suppose to give the interceptor on Fri. 9-17-2010 Just scared because I have always been told that you do not give interceptor to dogs with heartworm.


Hello, Kellie,

Sorry to be so late with a reply. I was out of town for several days.

The first heartworm preventive medicine was diethylcarbamazine, also known as D.E.C. This preventive had to be given daily. If given to a dog with heartworms, there was about a one in three chance that the dog would die - Russian Roulette with two bullets.

The monthly preventives have carried warnings not to give to dogs unless they are tested negative for heartworms. Now that these drugs have been around for quite a while, we find that the risk is not as high as previously thought.

Selamectin (Revolution) is actually FDA approved as safe to be given to dogs that already have heartworms.

The big boys in heartworm research tell us that ivermectin (Heartgard) is
safe to use in heartworm-infected dogs, and actually recommend it when starting a dog's treatment regimen. Several have told me that they don't think that milbemycin (Interceptor) is as safe.

That being said, I have had numerous patients who were taking Interceptor and got heartworms anyhow (missed dose or whatever) continue taking the medicine through their heartworm treatment with no trouble.

It sounds like your veterinarian has had a similar experience, and isn't worried about it. While the "authorities" recommend a different medicine, the risk with the Interceptor appears to be low. In my own practice, if the dog has not been on a heartworm preventive, we are starting them with Heartgard in cases like this.

If you have misgivings, it is better to discuss them with your veterinarian directly.

Good luck.

Brittany Miser

Hello, I'm in a bit of a pickle. My 9yr old pit bull lola-mae tested positive LAST year for adult heartworms. My vet at the time chose not to proceed with ANY treatment aside from her monthly heart guard and chose not to inform me at all, instead to inform his assistant. A full year later, my new vet strongly disagreed with his conclusion and quickly began treatment just as you have recommended. I was only informed after she reviewed our file this week. My question is how much more "risky" is it now, one full year after positively tested, and I'd like to note that she receives her monthly dose of heart guard all year and I've never missed a treatment. P.s. her proin treatment for urinary incontinence is now failing almost completely due to treatment...


Hello, Brittany,

Since you have been giving the heartgard regularly, there shouldn't be any more heartworms than there were one year ago. Any increase in risk would probably be minimal.

I assume the dog is taking some kind of corticosteroid like prednisone if you are having incontinence problems. That will get better when you get off the steroid.

Suzy Mongeon

In January I adopted a dog who had recently been treated for heartworm with 2 injections of Immiticide. According to the rescue group, he was asymptomatic and the worms were found during routine tests. I did some reading but apparently not enough, and didn't realize the importance of keeping him quiet during the recovery period. He did go on Doxycycline when my vet noticed a cough reflex in his initial exam, right after he arrived from Tennessee. His vet down there had sent a dose of Ivermectin which I gave a month later. About 2 weeks ago he had a coughing fit which prompted another visit to the vet and a prescription for Baytril. When he failed to improve and actually seemed to go downhill in terms of appetite and energy we went back to the vet. His temperature has gone from 102.1 (previous visit) to 104.7 and his white blood cell count is low. Also he has some abdominal discomfort. He's had x-rays - abdominal (showed a little buckshot!)and chest - bloodwork of course, now is on Cephalexin. We are treating symptoms of an upper respiratory infection, but I'm afraid the real problem is the dissolving worms and my ignorance! Lee is mixed breed and just under 20 pounds. He eats but not with his usual gusto, bowel movements seem okay, drinks water as usual. He just isn't improving and the bills are piling up. I am determined to get him through this! Any advice? Would Prednisone be helpful at this point?


Hello, Suzy,

The worms are usually pretty well gone by six weeks after the injections. It is certainly possible that the breakup of the worms caused some damage that has predisposed your dog to a respiratory infection. However, it is not likely that there are still worms present.

I understand your concern. Sometimes a low dose of corticosteroid (like prednisone) for a short period of time helps with the inflammation in a respiratory infection.

If antibiotics don't seem to be helping, I do worry about a fungus infection like blastomycosis or histoplasmosis. Regular antibiotics do not work for these. Mira Vista laboratories can do a test for these using a urine specimen.

IF fever is down and he is improving on the antibiotics, I would stay the course. It is unlikely that dissolving worms are still a factor.

It sounds like your veterinarian is being very thorough.

Sallie dim

My dog just tested positive for heartworm along with arthritis and has tested positive for Lyme's and antiplasmosis for years..we brought him in because of joint stiffness as he gets that each summer it seems from perhaps the Lyme's and doxy clears it up but the vet insisted we come in and claims the two tests for h worm were positive and inactive microfilaria were seen in blood.. Started on doxy and gabapentin but worried about prednisone side effects and very worried about the h worm shots...is the prednisone for the arthritis or to help with the dying worms not hurting and clogging his organs and at age 11 do you feel the slow treat ongoing hrehreartguard is a more reasonable option? Of course after the appt and a couple doses of vetformin he's running around looking fine but panting more so I am hopeful we're not getting duped...


Hello, Sallie,
Doxycycline is an antibiotic that is the drug of choice for tick-borne diseases, like Lyme. It also has some anti-inflammatory effects.

Gabapentin is believed to be helpful with pain associated with nerve inflammation.

I don't know what vetformin is.

Prednisone is a potent anti-inflammatory. It would certainly help relieve arthritis. With heartworm disease, we use it to reduce the swelling in the wall of the arteries where the worms are banging around. This keeps the arteries more open, and lets the blood flow more freely. There is less damage in the lungs, and it is easier for the heart to pump the blood through the lungs.

Prednisone has other effects in the body. It can cause fluid retention in some patients. It can affect carbohydrate metabolism. Too much can suppress the body's defenses. Long term excessive use causes even more problems.

It can be very safe when dosed properly, and very beneficial. It depends on what is going on the the individual dog.

It sounds like you have been working with this doctor for years. I doubt you are being duped. If in doubt, you could take the dog to another doctor for testing.

The doxycycline can cause death of the baby heartworms in the blood, causing a temporary false negative test. However, the antigen test for adult heartworm protein in the blood would not be affected.


I rescued a chihuahua with Heartworm 2 months ago! She was treated in May with 2 shots of Immitcide. We brought her home a week later kept her low key! Took her to my vet cause she also had giardia and tape worm, treated for that also! Kept on pregnisone for cough she developed! 1/4 5 mg pill 10 days then 1/8 for ten days! She's still coughing and it's now just about 2 months later!
I did wind up at the ER one night after taking interceptor, she was having trouble breathing! It's time for her Heartworm med again and I'm worried about giving her the interceptor!


Hello, Lorraine,

It is unusual to still have coughing at this time. You really should get her to your veterinarian for a recheck examination. It may be residual damage from the heartworm break-up (might need some more prednisone), or it could be something entirely different. Don't just assume it is the heartworm treatment.

Interceptor is usually very safe. It is not recommended to give if the dog has baby heartworms circulating in the blood.

Of course, it is possible that your dog just doesn't do well with the product. Some people cannot take an aspirin without getting sick. So, any medicine could be a problem.

Talk with your veterinarian about this. If you decide together to go with Interceptor again, be sure to give early in the day so that any problems can be seen during regular hours and save that emergency fee.

Melissa R Hulsey

My vet did not use doxycycline prior to the two Immiticide shots back to back, but said he would be on it afterwards. Is this ok?


Hello, Melissa,
My understanding is that the doxycycline prior to the Immiticide injections is used to inhibit the Wohlbachia organism that is beneficial to the heartworm. This makes the heartworms weaker and physically smaller, thus easier to kill and less for the body to dissolve afterward.
Giving it afterward would have an anti-inflammatory effect, which could help the body deal with the breakup of the dead worms.
I'm sure your doctor has a good reason for doing the treatment as he is. It is not possible for me to know your case like the doctor who is actually seeing your dog.

Alison Howe

I adopted my dog 2 years ago. She was heart worm negative for those 2 years and has been on Sentinel since being rescued. Her annual appointment she came up positive for heart worm. Her records showed her last vet had underdosed her. She was on up to 25 lbs and weight 27 lbs. We live in MA so heart worms are not very common. Now they want to start treatment. I'm so confused to how this could have happened and what to do? She tested negative for reproduction so it's what's in there now. I hate to put her through this.


Hello, Alison,

I understand your reluctance. I can say that she probably has very few heartworms, so is unlikely to experience much in the way of side-effects when the worms die and shift position.

When you say "negative for reproduction" I assume you mean that there were no microfilariae (microscopic baby heartworms) in the blood. The main importance of this would be dog being more likely to have a bad reaction when taking heartworm preventive if babies were present.

The absence of babies in the blood doesn't really tell you anything about the number of worms or severity of disease.

In this case, you've been on preventive, but at a slightly low dose. This is why I suspect that you have very few worms present.

You should also know that if there are fewer than four adult female worms present, the tests can give a false negative result. This means it is possible that your dog has had a very small number of worms all along, and that things are no worse than they have been.

Again, I would not expect many problems with the treatment in your situation. As always, the doctor best equipped to advise you is the one actually seeing your dog.

You should discuss your concerns with him/her.


Hello, my dog Tinker (chihuahua) has been diagnosed with heart worm. The vet immediately put her on
Doxycycline and Prednisolone with a monthly Dose of Tri-Heart Plus. Tinker has been taking as prescribed and with food for ease on the tummy. She seems to be having no issues with the meds, but I have noticed a little cough here and there. Is this normal? I have read that while the worms are dying a cough may develop, could this be the case?

Thank you for your time!
Extremely worried doggy Mommy


Hello, Colleen,

It is very unlikely that there are any worms dying at this point.

If the cough continues, you should let your veterinarian re-examine the dog.

Tammy Rourke


I recently adopted a Rottweiler X from the local shelter. During her stay at the shelter, she was treated for heartworm, with her last treatment on Oct. 22. 2017. I would like to know if it is safe to give the Interceptor Plus I received from her new Vet immediately or if I should wait until Nov. 22. I don't want to leave her vulnerable or inadvertently make her sick. Also, I'm wondering if it is necessary for her to be on the "Plus" preventative, as I am concerned about possible side effects.

Thanks for your attention to my query.

Tammy and Gypsy


Hello, Tammy,

The safety of the Interceptor Plus would depend on whether there are circulating microfilariae (microscopic baby heartworms) in the blood. If so, some dogs are more likely to have a bad reaction with milbemycin (the active ingredient) than they are with the low dose of ivermectin found in Heartgard. You should talk with your veterinarian about this.

In Interceptor Plus, the plus refers to the addition of praziquantel, which kills tapeworms in the bowel. The milbemycin can kill hookworm, whipworm and roundworm in the bowel. The "Plus" part is super safe, not a problem.

In Heartgard plus, the plus refers to pyrantel pamoate, which kills hookworm and roundworm in the bowel. Also super safe.

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