Canine Heartworm Disease Prevention

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By Dr. Erin Troy DVM, CCRP

We are all struggling right now with the right choice of  heartworm prevention for each dog.  There have been supply issues with established products as well new products that we may be unfamiliar with and it makes it all very confusing.

Let’s start first with the basics that can clear up some misunderstandings.  According to Dr Mark Kittleson DVM PhD DACVIM ( Cardiology) at UC Davis, all heartworm preventatives are from the macrocyclic lactone family. This  family is further divided into avermectins, which includes ivermectin as in Heartgard Plus, and milbemycin which is in Interceptor, Sentinel and Trifexis.  Even more important to know is that the amount of ivermectin in Heartgard Plus is not now nor ever has been toxic to ANY breed of dog regardless of MDR1 status.  The dose of ivermectin in Heartgard Plus,  6-12mcg/kg,  is far too low to cause a toxicity.  Ivermectin toxicity  occurs at a dose of 50mcg/kg in the MDR1 mutant dogs and at a dose of  > 100mcg/kg in non- mutant dogs. Keeping this in mind, Heartgard Plus is a safe option for heartworm prevention in any dog. There are occasions where ivermectin can be prescribed at much higher doses than is present in Heartgard Plus and this would not be done in a dog suspected or confirmed sensitive to ivermectin .    If you are still not convinced that you want to put your dog on an ivermectin containing product, then  the milbemycin-containing products such as Trifexis, Sentinel and Interceptor would be another option that is just as safe for monthly protection.  (Sentinel and Interceptor are not currently in production as of the writing of this article).

I hope that this helps put your mind at ease and makes it easier for you to make the right choice for your dog.

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