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How to Talk to Your Veterinarian About Your Dog’s MDR1 Result

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By knowing your dog’s genetic risk for MDR1 drug sensitivity, you and your veterinarian can take steps to make sure that your dog doesn’t have a bad reaction to certain drugs.

What is MDR1?

Multidrug Resistance 1 (MDR1) is caused by a genetic variant in the ABCB1 gene. Dogs who have this genetic variant are sensitive to certain types of drugs.

This genetic variant is common in herding breeds, including Australian Shepherds, Collies, and Border Collies, though it also affects many other breeds.

Dogs with MDR1 drug sensitivity have severe, sometimes life-threatening reactions to certain medications. Signs of MDR1 drug toxicity are primarily neurological. They include:

  • Weakness
  • Tremors
  • Lethargy
  • Seizures
  • Coma
  • Vomiting
  • Diarrhea 

What should I tell my veterinarian?

If you know your dog’s genetic risk for MDR1 drug sensitivity, there are simple ways to prevent a reaction from happening.

Start by sharing your dog’s Embark health results with your veterinarian. Let them know that your dog has the genetic variant associated with MDR1, so they can flag it in your dog’s medical file.

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Not all drugs result in adverse reactions related to MDR1 sensitivity, so ask your veterinarian if your dog’s care plan involves any of the problem drugs. Common drugs that may cause toxicity in MDR1-affected dogs include the anti-parasitic medication ivermectin, other anti-parasitic drugs, some pre-anesthetic medications, and some cancer drugs. Your veterinarian might recommend lowering the dosage of a current medication or using a different drug instead. For more information, refer to the full list of drugs affected by MDR1 published by Washington State University.

It’s also important to note that even if your dog has the MDR1 genetic variant, it doesn’t necessarily mean that they shouldn’t receive the drug at all. For example, most once-monthly parasite preventatives can be used safely in MDR1-affected dogs, because the doses needed for prevention are lower than other applications. Other drugs may also be safer at lower doses, even for dogs with MDR1. Your veterinarian can advise on the right dosage for your dog.

Always speak to your veterinarian before discontinuing or changing the dosage of any medication your dog is currently taking.

What does MDR1 mean for my dog?

Once it’s identified, MDR1 drug sensitivity is easily managed by avoiding the problem drugs. Your veterinarian can advise on the appropriate drugs and doses for your dog. In many cases, alternate medications can be used instead, or your veterinarian can prescribe a lower, safer dose.

Mimi Padmabandu Contributor

Mimi Padmabandu is a scientific writer and Content Strategy Lead at Embark Veterinary. She has over a decade of experience writing about science and genomics for leading biotechnology companies. She holds a bachelor's degree in Molecular, Cell, and Developmental Biology from UCLA and a master’s degree in Early Modern English Literature from King’s College London.

Read more about Mimi Padmabandu

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