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Mutant and Proud

Is your dog a Mutant? Not like Professor X from X-men. I mean, does your dog have a mutation to the MDR1 gene (but perhaps if we were talking X-men we could call this particular mutant MD Resisto)! The MDR (multi-drug resistance) gene is responsible for protecting the brain by transporting potentially harmful chemicals away. The MDR1 mutation allows the drugs to build up in the brain, where they can cause ne urological reactions including disorientation, seizures, and blindness. Your veterinarian may discuss the MDR1 gene mutation in more depth with you if your dog is one of the following breeds:


The MDR1 gene mutation makes affected herding breed dogs especially sensitive to the negative effects of certain medications that are typically tolerated including common drugs like Ivermectin and Imodium (loperamide).  Ivermectin… and herding dogs… It seems to go hand in hand, doesn’t it? Herding dogs are often found where there are livestock. Ivermectin is a common intestinal parasite dewormer used for livestock. This means that if your canine assistant is an MDR1 mutant, you will need to take extra precautions when deworming your livestock. If the affected dog were to ingest some of the horse/livestock Ivermectin dewormer paste or the manure from the recently de-wormed animal, symptoms of an Ivermectin toxicity could present shortly after. While equine dewormers contain high doses of Ivermectin, the ivermectin dose in heartworm preventatives, like Iverhart and Heartgard, are so low that they would not pose a risk to a dog with the mutation.


Lucky for us, this gene mutation can be tested for. Talk to your veterinarian about testing your herding breed or mixed breed dog for the MDR1 gene. A quick cheek swab or blood sample can be submitted to Washington State University for testing. Results are sent to you and a copy to your veterinarian in 1-2 weeks. The MDR1 gene is also tested for in the common canine DNA test: Wisdom Panel. This information will help to make lifestyle choices and medical decisions based on your dog’s results.

Normal/Normal Results: These dogs do not carry the mutation, and will not pass on the mutation to their offspring. These dogs would not be expected to experience unexpected adverse drug reactions to normal doses of Ivermectin, loperamide, and some anticancer drugs.

 Mutant/Mutant Results: These dogs carry the mutation and can not pass on a normal gene to their offspring. These dogs would be expected to experience toxicity after normal doses of loperamide, some anticancer drugs, and high doses of Ivermectin.

Normal/Mutant Results: These dogs carry the mutation and may pass the mutant gene to their offspring. For this reason, we do not recommend mutant/mutant dogs be used for breeding purposes. These dogs may experience toxicity after normal doses of loperamide, some anticancer drugs, and high doses of Ivermectin.

Visit the Washington State University website for a list of problem drugs for MDR1 gene mutation dogs:


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