MDR1 Multidrug Sensitivity

About MDR1 Multidrug Sensitivity

TSCR_MDR1 Introduction Infographic FINAL

MDR1 refers to the canine Multidrug Resistance 1 gene, which codes for a protein that helps certain drug compounds cross the cell membrane. Mutations in MDR1 can “break” the protein, preventing those drug compounds from crossing properly. This puts dogs with MDR1 mutations at risk of experiencing severe—and potentially life-threatening—complications from those drug compounds.

Every dog has 2 copies of the MDR1 gene: One is inherited from their mother, and the other from their father. A dog’s drug sensitivity risk depends on their MDR1 mutation status. Having 2 mutated copies of MDR1 puts a dog at high risk of complications from taking medications that need the MDR1 protein’s help to move into and out of cells.

MDR1 mutations are most common in herding dogs, like Collies, Australian Shepherds, Shelties, and Border Collies. Around 70% of Collies have at least 1 mutated copy of the MDR1 gene. The Washington State University College of Veterinary Medicine’s Program in Individualized Medicine (PrIMe) maintains a list of dog breeds most commonly affected by MDR1 mutations.

Some drug compounds are known to pose health risks for dogs with one or two mutated copies of MDR1. The MDR1 mutation was actually first discovered due to observed sensitivities to ivermectin in some dogs. MDR1 multidrug sensitivity has since been extensively researched, and PrIMe maintains a list of problem medications for dogs with this genetic condition.

Some drugs of concern can be safely used with dogs who have the MDR1 mutation, but only at certain doses. For example, research has shown that ivermectin and related parasite prevention drugs are safe for these dogs at the FDA-approved doses for heartworm prevention, but NOT at the doses required to treat other conditions, such as mange. Other drugs, like loperamide (Immodium) are toxic at even the lowest therapeutic dose and should be avoided at all costs.

In an online summary of MDR1 multidrug sensitivity, the American Animal Hospital Association says that when possible, choosing an alternative drug to accomplish the same therapeutic effect is recommended for dogs with known or suspected MDR1 mutations. If this isn’t possible, dosing recommendations are available through individual consultations with PrIMe.

The infographic on the right shows PrIME’s problem drugs list in a table that was adapted from those displayed on both PrIME’s website and the Collie Health Foundation website. We hope that it’s helpful in learning which medications may be dangerous for dogs with the MDR1 mutation.

TSCR MDR1 Problem Drugs infographic FINAL
MDR1 Genetic Testing Infographic FINAL

Commercially-available DNA tests can determine a dog’s MDR1 mutation status. MDR1 DNA testing uses a cheek swab or blood sample from a dog to check for the presence of the MDR1 mutation.

The possible results of the MDR1 genetic test are:

  • Normal/Normal: These dogs do not carry the MDR1 mutation and cannot pass it on to their offspring. They are not at risk of adverse reactions from taking MDR1 problem drugs.

  • Normal/Mutant: These dogs carry the MDR1 mutation and can pass it on to their offspring. They are at risk of adverse reactions from taking MDR1 problem drugs.

  • Mutant/Mutant: These dogs are affected by the MDR1 mutation and will pass it on to all of their offspring. They are at high risk of adverse reactions from taking MDR1 problem drugs.

If your dog is a herding breed, or you would otherwise like to check to see whether they have the MDR1 mutation, ask your veterinarian about getting a DNA test. These tests are commercially available through a number of companies, programs, and laboratories, including:

At TSCR, we perform an MDR1 genetic test on every rescue Collie who comes through our program. This helps to ensure that their forever families and veterinarians know their exact risk for MDR1 multidrug sensitivity.

Getting your dog’s DNA with a cheek swab for an MDR1 genetic test is actually pretty simple! Watch our “Indiana Bones and the MDR1 Genetic Test” Reel on Facebook or on Instagram to see just how easy the process is!

TSCR Indiana Bones and the MDR1 Genetic Test