Multidrug resistance mutation 1 (MDR-1) is an inherited genetic mutation that causes dogs to be more sensitive to certain medications. When given these drugs, animals with the MDR-1 gene mutation can suffer from severe and potentially life-threatening reactions.
Causes of MDR-1 Mutation
Some dogs are born with a mutation in the MDR-1 gene, which is responsible for transporting certain chemicals out of the brain. Without the protection this gene provides, some types of medications can build up in the brain and cause serious neurological reactions.
MDR-1 mutation is most commonly seen in herding dog breeds including collies, Australian shepherds, English shepherds, and old English sheepdogs. Mixed breed dogs can also be affected.
Medications to Avoid
If your dog has the MDR-1 mutation, it is vital to avoid giving them certain medications. The following is a list of some of the most common medications to avoid.
- Antiparasitic drugs including ivermectin (in high doses), milbemycin, moxidectin, and selamectin
- Antibiotics such as rifampin and erythromycin
- Anti-cancer drugs such as doxorubicin, vinblastine, and vincristine
- Anti-diarrheal drugs such as loperamide (Imodium)
- Painkillers such as butorphanol
- Tranquilizers such as acepromazine
Symptoms of Drug Reaction
Dogs with the MDR-1 mutation can suffer from severe reactions to the above medications. These include seizures, disorientation, loss of balance (ataxia), respiratory problems, coma, blindness, and even death. Please seek emergency medical care if your dog develops a reaction to any medication they are given.
Testing for MDR-1 Mutation
If your dog is a herding breed, it is important to have them tested for the MDR-1 mutation so your veterinarian knows which medications to avoid prescribing. Fortunately, testing is simple and inexpensive. Please ask your veterinarian for more information about testing if your dog is a herding breed, or if you otherwise suspect they may have the MDR-1 mutation.
