MDR1 (Multi-Drug Resistance 1) in dogs refers to a genetic mutation in the ABCB1 gene that makes them hypersensitive to certain common medications, potentially causing severe or fatal reactions because a protective protein (P-glycoprotein) doesn't work correctly, allowing drugs to build up in the brain. This condition, common in herding breeds like Collies and Australian Shepherds, requires owners to avoid specific drugs (like some antiparasitics and opioids) to prevent neurotoxicity, with genetic testing being the best way to know if a dog is affected.

What does it mean if a dog is a carrier of MDR1?

Overview. Multidrug Resistance 1 (MDR1) drug sensitivity is the result of a genetic variant that can place dogs at risk of severe or life-threatening complications after taking particular medications at specific doses.

What dog breeds cannot have ivermectin?

Dogs that cannot have ivermectin, or are at high risk for toxicity, are primarily herding breeds (like Collies, Australian Shepherds, Shelties) with the MDR1 gene mutation, which impairs their ability to clear the drug, making high doses dangerous. Other sensitive breeds include German Shepherds, Old English Sheepdogs, and Long-Haired Whippets, though mixed breeds can also carry the mutation, requiring caution and potential genetic testing, as even small amounts can cause severe reactions. Doses in heartworm preventatives are usually safe, but higher doses (like for mange or equine wormers) are very risky. 

What to avoid with the MDR1 gene?

Below is a list of drugs that should be generally avoided in dogs with an MDR1 status, or herding breeds or mixed breeds of unknown MDR1 status.

• Ivermectin.
• Selamectin.
• Milbemycin.
• Moxidectin.
• Loperamide.
• Acepromazine.
• Butorphanol.
• Vincristine.

Can dogs with MDR1 have Heartgard?

The FDA determined Heartgard is safe for dogs with the MDR1 mutation when used at label doses. For other formulations of ivermectin contact MDR1Caddie™ for dosing recommendations. At doses used to treat diarrhea, this drug will cause neurological toxicity in dogs with the MDR1 mutation.

Ivermectin and the MDR1 Gene Mutation in Herding Dogs?! | Veterinarian Explains

What is the best heartworm prevention for dogs with MDR1?

Ivermectin and related drugs (milbemycin, selamectin) are commonly used in the prevention and treatment of parasites. They are common components of most canine heartworm preventives. At low doses, such as those used in heartworm prevention, ivermectin is safe even for dogs with the MDR1 mutation.

How much does it cost to test for MDR1 in dogs?

Dog Multidrug Resistance 1 (MDR1) Test

The price of the Dog MDR1 Test starts from $69.

What is the leading cause of death for border collies?

In fact, your Border Collie's life span may even be cut short by one to three years! Cancer is a leading cause of death in older dogs. Your Collie will likely live longer than many other breeds and therefore is more prone to get cancer in his golden years.

Is Heartgard just ivermectin?

Yes, Heartgard contains the active ingredient ivermectin (in combination with pyrantel in Heartgard Plus) and works as a monthly preventative for heartworm disease, as well as treating/controlling hookworms and roundworms in dogs and cats. The ivermectin kills heartworm larvae before they can mature, protecting against the disease, and the medication requires a veterinary prescription.

Is ivermectin toxic to all dogs?

Any dog that consumes a large amount of horse manure containing ivermectin could become very ill. But some dogs of certain breeds have a gene mutation which puts them at risk of poisoning from ivermectin, even if they ingest a small amount. Breeds at risk include: collies.

What does "white feet don't treat" mean?

A common adage at the time was “white feet, don't treat,” meaning that dogs with white feet were thought to be more susceptible to ivermectin toxicity. Because of early reports of ivermectin toxicity in collies, that breed became the early model for researchers to discover more about this genetic mutation.

Do vets recommend dog genetic testing?

Yes, many veterinarians recommend dog genetic testing, especially for health screening, to personalize care, predict risks for breed-specific diseases (like MDR1 sensitivity), and allow for early intervention, though they stress using results cautiously with a vet to avoid misinterpretation, as tests are often prognostic (predictive) and not always diagnostic. It helps owners manage potential issues like drug sensitivities or certain inherited conditions, leading to better long-term health management and outcomes, fitting well into wellness plans for puppies and new patients.
 

What are the first signs of DM in dogs?

Initial signs include loss of coordination (otherwise called ataxia) in the hind limbs; swaying or wobbling when walking; rear feet knuckling over or dragging; and difficulty with walking up steps, squatting to defecate, or getting into the car.

What are signs a dog is reacting to medication?

The most common symptoms of drug reactions include:

• Vomiting.
• Diarrhoea.
• Lethargy.
• Reduced or increased appetite.
• Increased thirst.
• Skin reactions: itching, redness, hives and hair loss.
• Drooling.
• Sedation.

Do Border Collies pick a favorite person?

Border Collies thrive on the physical closeness and security that comes from snuggling with their favorite person. This behavior also reinforces the bond between you and your dog, providing them with a sense of belonging and emotional connection.

How common is MDR1 in dogs?

The MDR1 mutation is often associated with herding breeds, such as collies, Australian shepherds, and Shetland sheepdogs. The mutation is most prevalent in collies (up to 70%). Up to 50% of other herding breeds will have the mutation.

What is the new name for MDR1?

The source of the resistance was traced back to P-glycoprotein, and, because of this, the gene encoding it was named Multidrug Resistance 1, or MDR1. Later, the gene name was changed to ABCB1, and both notations are still used today.

Is MDR1 hereditary?

The defective p-glycoprotein allows a higher level of drugs to enter the brain leading to an increased sensitivity to certain drugs and increasing the toxic neurologic side effects of some medications. The MDR1 gene mutation is hereditary and is passed from parents to offspring.

What dewormer is used for MDR1 dogs?

Drugs such as ivermectin, selamectin, milbemycin, and moxidectin, are commonly used to treat and prevent parasites like heartworms. At low doses, such as those used in heartworm prevention, these drugs have been shown to be safe even for dogs with the MDR1 mutation.

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