What is the MDR1 gene?

MDR1 stands for Multi Drug Resistance 1, also known as the MDR1 mutation or multi drug sensitivity. This genetic mutation affects how certain medications move through a dog’s brain and body.

Dogs with the MDR1 mutation have a change in a gene that normally produces a protein responsible for pumping certain drugs and toxins out of the brain. When this gene does not function properly, some medications can accumulate in the brain and cause neurological toxicity.

It is important to understand that MDR1 does not affect a dog’s overall health, lifespan, or quality of life. Dogs with this mutation live completely normal lives. The only difference is that certain medications must be avoided or used carefully.

Why breeders do not eliminate every MDR1 carrier

As responsible breeders we give preference to dogs that test Normal/Normal for MDR1 whenever possible. However, completely removing every carrier from breeding programs would drastically reduce the genetic diversity of the Australian Shepherd gene pool.

When a gene pool becomes too small, other serious genetic diseases can become more common. For this reason, responsible breeding programs often pair MDR1 carrier dogs only with MDR1 clear dogs so that no puppies are affected with two copies of the mutation.

Genetic diversity is critical to the long term health of the breed, so MDR1 status is evaluated along with many other health and structural factors when making breeding decisions.

How MDR1 is inherited

Each puppy receives one copy of the MDR1 gene from each parent.

A dog may be:

Normal/Normal (clear)

The dog does not carry the mutation and will not pass it to offspring.

Carrier (Normal/Mutant)

The dog carries one copy of the mutation but usually does not show drug sensitivity.

Affected (Mutant/Mutant)

The dog has two copies of the mutation and is sensitive to certain medications.

Because the mutation is very common in herding breeds such as Australian Shepherds, many veterinarians automatically treat the breed as if they may carry MDR1 to ensure medications are used safely.

At Raised Right Pups we always recommend discussing MDR1 status with your veterinarian so they can take it into consideration when prescribing medications.

Medications that can be dangerous for dogs with MDR1

Some drugs that may cause toxicity in MDR1 sensitive dogs include:

Ivermectin at high doses

Selamectin

Milbemycin

Moxidectin

Loperamide (Imodium)

Acepromazine

Butorphanol

Vincristine

Vinblastine

Doxorubicin

Paclitaxel

Apomorphine

Medications that appear to be tolerated in most MDR1 dogs

These drugs are transported by the MDR1 pathway but are generally considered safe when used appropriately by a veterinarian.

Cyclosporine

Digoxin

Doxycycline

Morphine

Buprenorphine

Fentanyl

Common medications veterinarians use cautiously

Acepromazine, a tranquilizer, may require lower doses

Butorphanol, a pain medication, may require lower doses

Moxidectin, an antiparasitic drug

Certain chemotherapy drugs such as vincristine, vinblastine, and doxorubicin

Heartworm prevention and MDR1

Heartworm preventatives are considered safe for MDR1 dogs when used at the FDA approved preventative doses. The issue typically arises only with extremely high doses of certain medications.

Final note for Aussie owners

Because MDR1 is common in herding breeds, many veterinarians automatically take precautions when treating Australian Shepherds. Even if your dog has never been genetically tested, informing your vet that your dog is an Aussie allows them to make safe medication choices.

When handled properly by an informed veterinarian, MDR1 is simply a management consideration and does not impact a dog’s ability to live a healthy, happy life.

Why Raised Right Pups performs genetic testing

At Raised Right Pups, genetic health testing is a critical part of how we protect the future of the breed while producing healthy, well balanced puppies for families.

Every breeding dog in our program undergoes extensive DNA testing before being considered for breeding. This allows us to identify carriers of certain genetic traits and make responsible breeding decisions that protect the puppies we produce.

Genetic testing does not mean a dog is unhealthy. Many perfectly healthy dogs can carry a single copy of a gene without ever experiencing symptoms. The purpose of testing is to understand what each dog carries so we can pair dogs responsibly and prevent puppies from inheriting two copies of harmful mutations.

For example, with the MDR1 gene we can safely breed a carrier dog to a dog that is clear. This ensures no puppies will inherit two copies of the mutation while still preserving valuable genetics in the breed.

Responsible breeding is about balance. Completely removing every dog that carries a mutation would dramatically shrink the gene pool and can actually increase the risk of other genetic diseases appearing over time. Instead, responsible breeders evaluate the full picture including health testing, temperament, structure, pedigree, and overall contribution to the breed.

Through careful planning and responsible genetic testing, our goal is to produce puppies that are healthy, stable, and set up for a long life as beloved family companions.

For puppy owners, this testing also provides valuable information for your veterinarian so they can make the safest medical decisions for your dog throughout its life.

For full transparency, the genetic testing results for each of our parent dogs are publicly available. You can view all DNA health testing directly on our GoodDog profile under each individual dog’s page.

This allows our families to see exactly what testing has been performed and provides complete transparency in our breeding program.

Resources

Washington State University Veterinary Clinical Pharmacology Laboratory

https://vcpl.vetmed.wsu.edu

American Kennel Club Canine Health Foundation

https://www.akcchf.org

UC Davis Veterinary Genetics Laboratory

https://vgl.ucdavis.edu

Merck Veterinary Manual

https://www.merckvetmanual.com

American College of Veterinary Clinical Pharmacology

https://www.acvcp.org