Are collies sensitive to heartworm prevention drugs?

Our question this week was:

I have a collie and I heard they are sensitive to one of the drugs that treats heartworm disease. Do you know anything about it?

Julie B. O'Fallon, MO


Hi – thanks for your email. Some collie breed dogs (and other breeds) are sensitive to a drug called Ivermectin. Some breeds have an autosomal recessive trait (MDR-1) gene has been identified that causes a defect in the p-glycoprotein multidrug transporter to the blood brain barrier. This allows for the ivermectin pass into the brain at low dosages thus causing toxicity.

Breeds believed to be sensitive to Ivermectin include the collie, Australian shepherd Shetland sheepdogs, Old English sheepdogs and English sheepdogs although not every "sensitive" animal in the breed is affected.

If you have one of these breeds, you may want to test your dog for the MDR-1 gene. An article that might be helpful to you is Ivermectin Toxicity in Dogs. This link includes information about the laboratory that does the MDR-1 gene testing.

Best of luck!

Dr. Debra

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