Several years ago a mixed breed patient came in with a severe case of vomiting, lethargy, and tremors. The owner and the veterinarian suspected he had gotten into some kind of toxin, but weren’t sure exactly what. After the owner agreed to hospitalize the dog for the day and have bloodwork run, the dog was then given Cerenia intravenously to control the vomiting and nausea. Shortly after, the treatment technician yelled for the doctor from across the hospital, because their patient was now seizing. Valium was given to control the seizures and once the dog was stable, activated charcoal was given in an attempt to absorb any toxins that may still be in his system. I remember this dog well because he was the only patient I had that willingly ate his activated charcoal straight out of a bowl. We didn’t need to syringe feed him!
It was agreed to send additional bloodwork to the lab to rule out underlying conditions. Everything came back normal and the dog recovered and was sent home. Fast forward to a few weeks later and this dog returned with the same symptoms. Again, the owner didn’t know what he could have gotten into. After some Q&A between the owner and the veterinarian it was discovered that the owner had been giving this dog Acepromazine that was prescribed to their other dog for a firework phobia. With this new information, combined with the dog’s seizure shortly after being given Cerenia during his hospitalization, the doctor asked if we could send more bloodwork to the lab and included the MDR1 testing. The dog was put on supportive care in-hospital and was sent home once he was stable. The owner was given explicit instructions to not give him any medications until the lab results came in. Turns out, he had the MDR1 mutation.
What Is The MDR1 Gene Mutation
MDR1 stands for Multidrug Resistant 1. This is a genetic mutation that leaves the dog at risk for life threatening complications to particular drugs. Essentially, the mutation causes the body to not be able to eliminate certain drugs, leading to a toxic buildup and can even cross into the brain. The drugs that are most concerning for MDR1 dogs at normal dosing and should be avoided include, but are not limited to; Acepromazine, Butorphanol, chemotherapy drugs, Cyclosporine, Galliprant, Imodium, Cerenia, and Ondansetron. Drugs that have been determined to be safe at low dosing or given within the labeled dose, but should be avoided at high dosing include ivermectin (Heartgard), milbemycin (Interceptor), and selemectin (Revolution).
Testing
The only way to determine if a dog has the MDR1 mutation is with genetic testing. Testing can be done at your regular veterinary office and shipped to the lab, or you can order a canine DNA test through any of the various genetic testing companies that offer health panels. Embark and Wisdom Panel both offer a breed and health panel that includes MDR1 testing.
Breeds Of Concern
The MDR1 mutation can affect any dog breed or mix but it is certainly more prevalent in Collies and Australian Shepherds. It is estimated that 70-75% of Collies have the MDR1 mutation. When I say Collie, I’m not talking about Border Collies or Shetlands, this is just the Collie line. Your typical “What’s that Lassie? Timmy fell down the well?” dog. If you have a Collie or Collie mix, it is highly recommended to have your dog tested for MDR1 mutations. Australian Shepherds (even mini aussies) are estimated that 50% of the population has the mutation.
Many clients and even veterinary staff assume that all herding dogs are likely to have this mutation and many websites state this, but that simply isn’t true. Less than 5% of Border Collies are affected and less than 10% of German Shepherds. For a full list, visit the Washington State University Veterinary Medicine website. Veterinary colleges everywhere have partnered with companies such as Embark to collect data on genetic health conditions to improve veterinary medicine and awareness.
It is recommended to have your Collies or Australian Shepherds tested for the mutation prior to breeding to ensure this gene mutation is not passed on to future generations. When looking for your next family member, ask your breeder what type of testing and veterinary care they provide for the parents and puppies. If you rescue a dog or choose to purchase a puppy from a breeder that does not do testing, it’s a good idea to have the testing done yourself, rather than waiting for a life-threatening reaction to a medication.
The vast majority of dog owners will never have to worry about the MDR1 mutation. While it is possible to have a mixed breed dog with this gene mutation, it’s certainly not common. Research and know the breed prior to making them a part of your family. The knowledge you gain will save you thousands of dollars in the long run!