Multi-Drug Sensitivity(MDR1 )


The MDR1 gene encodes P-glycoprotein,which plays an important role in limiting drug absorption and distribution in the brain, as well as enhancing the excretion of many drugs. Some dogs, particularly herding breeds, have a mutation in the MDR1 gene which limits their ability to prevent

drug absorption and distribution in the CNS. This can allow certain drugs to accumulate and remain in the brain at toxic levels.


Breeds at high risk

Typically herding breeds and mixes of these breeds are affected:

     American White Shepherds

     Australian Shepherd

     Border Collie

     English Shepherds

     German Shepherds

     Longhaired Whippet

     McNab Shepherd

     Old English Sheepdog

     Rough Collie

     Shetland Sheepdog

     Silken Windhound

     Smooth Collie



Dogs can be tested for MDR1 with a blood sample or cheek swab through their veterinarian or at home. Owners can easily order a test kit by contacting the Veterinary Clinical Pharmacology Laboratory at Washington State University: or by phone (509)335-3745, or a DNA testing company such as or Dogs only need to be tested once in their life. Dogs with as little as one copy of the gene should not consume the drugs listed below. It is important for owners to have a list of unsafe drugs so they can advocate for their dogs.


Unsafe Drugs














Clinical Signs

If a drug that is toxic to your dog was administered a buildup of toxins will start to occur and your dog will display neurological signs. This includes weakness, lethargy, disorientation, ataxia, tremors, seizures, blindness or death.



There is no cure for MDR1. The safest precaution is to avoid giving a drug that may place your dog at risk. Dogs that show signs of adverse drug reactions are treated based on their clinical signs with supportive care.



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