Today’s guest writer is Stacy Mantle. She is writing about how dogs process pain.  

If you’ve ever noticed that your dog reacts more intensely to certain types of medication, he may have a gene mutation known as MDR1  (Multi-Drug Resistance-1).

An MDR1 mutation means that your dog has two copies of the MDR1 gene and can’t properly process drugs that use a specific pathway (P-glycoprotein) to move the medication throughout their system. As a result of not being able to process the medication, the drugs begin to build up in your dog’s brain and eventually cause severe neurological reactions (ranging from blindness and tremors to death).

This gene mutation is very common in herding dogs (like shepherds and collies) and sighthound breeds (like Whippets and sheepdogs). There are many different breeds that can be affected with this mutation and honestly, you may not know if your dog is impacted without a test.

Does Your Dog React Differently to Medications?

How do I find out if my dog has this condition?

The only way to verify if your dog has this condition is to have a test done. Testing can be done through blood or saliva and will require your dog to be genotyped (which is a fancy way of saying they are looking at your dog’s DNA).

Either you or your veterinarian can perform the test required to see if your dog has an MDR1 mutation. Test kits are available from WSU’s Veterinary Clinical Pharmacology Lab, and while the kit to test is free, the sample will cost $60 to process.

Your veterinarian can also perform a blood test to see if your dog is sensitive. Still another method of testing your dog is to have their DNA checked by a company like Wisdom Panel. These DNA tests not only evaluate your pet for the MDR1 gene, but also tell you the breeds of your dog. The cost is nearly the same – $79.99. You will receive a kit that will help you get a sample of your dogs saliva, which you send in to Wisdom Panel. A few days later, you’ll receive a report that tells you your dog’s history and whether or not they are positive for MDR1.

If you discover that your dog does carry the extra MDR1 gene, there are precautions you should take. The first thing to do is discuss the findings with your veterinarian. If there is a possibility your dog reacts to medication in an unusual way, they should wear a tag that states they are sensitive to specific types of medication.

These are the prescription treatments that your dog should avoid:

Drugs to Avoid in Dogs with MDR1 Mutation

Pain Medication:

  • Acepromazine
  • Butorphanol

Cancer Treatments:

  • Doxorubicin
  • Inblastine
  • Vincristine


  • Erythromycin
  • Rifampin


  • Ivermectin (in high doses)
  • Milbemycin
  • Moxidectin
  • Selamectin


  • Loperamide (Imodium)

As always, be sure to check with your veterinarian about any changes to the list of medications. Our hope is to spread the information so more dogs can be happy and healthy and live long lives.

1 DOGTV is not affiliated with WSU or Wisdom Panel in any way.