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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.

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