Does your dog have the dangerous MDR1 mutation?


What is the the MDR1 Mutation?

MDR1 is the shorthand name for a gene called Multi-Drug Resistance 1.


A mutation in this gene causes sensitivity to many different drugs, most famously Ivermectin.  The mutation causes a defect in the transport system of the dogs brain.  So when given drugs, like Ivermectin, the medication flows to the brain, where it is not properly transported to the body, and subsequently builds up to toxic levels.  This buildup in the brain causes nuerological problems ranging from seizures to, in some cases, death.


Drugs that Cause MDR1 Interactions


  • Ivermectin
  • Selamectin
  • Milbemycin
  • Moxidectin
  • Loperamide(Imodium™)
  • Acepromazine
  • Butorphanol
  • Vincristine
  • Vinblastine
  • Doxorubicin
  • Paclitaxel


There are also some drugs that use the MDR1 gene transport system but have not been shown to cause adverse reactions in dogs with the mutation:


  • Cyclosporin
  • Digoxin
  • Doxycycline
  • Morphine
  • Buprenorphine
  • Fentanyl


There are a few drugs that are known to use the MDR1 transport system to be pumped from the brain in humans but have not yet been tested in dogs.  These drugs may or may not cause adverse reactions and should be used with extreme care in dogs with the mutation of the MDR1 gene.


  • Domperidone
  • Etoposide
  • Mitoxantrone
  • Ondansetron
  • Rifampicin


How to Test for the MDR1 Mutation


There are a number of tests on the market that will identify if your dog is positive for the MDR1 mutation.  Some are better than others, but the most comprehensive test available is from Mar’s Veterinary.  The test will also identify breed ancestry, a weight profile, and whether the dog has the MDR1 mutation.


More information on Mars Veterinary can be found here