Victorian Collie Rescue

Multidrug Sensitivity in Dogs

"What is Multidrug Sensitivity in dogs?"

Some dog breeds are more sensitive to certain drugs than other breeds. Collies and related breeds, for instance, can have adverse reactions to drugs such as ivermectin and loperamide (Imodium). 

Drug sensitivities result from a mutation in the multi-drug resistance gene (MDR1). This gene encodes a protein, P-glycoprotein that is responsible for pumping many drugs and other toxins out of the brain. Dogs with the mutant gene cannot pump some drugs out of the brain as a normal dog would, which may result in abnormal neurologic signs. The result may be an illness requiring an extended hospital stay - or even death.

"How do I know if my dog is affected?"

Approximately three of every four Collies in the United States have the mutant MDR1 gene. The frequency is about the same in France and Australia, so it is likely that most Collies worldwide have the mutation. The MDR1 mutation has also been found in Shetland Sheepdogs (Shelties). Australian Shepherds, Old English Sheepdogs, English Shepherds, German Shepherds, Long-haired Whippets, Silken Windhounds, and a variety of mixed breed dogs.

The only way to know if an individual dog has the mutant MDR1 gene is to have the dog tested. As more dogs are tested, more breeds will probably be added to the list of affected breeds.

"What drugs should I look out for?"

Many different drugs and drug classes have been reported to cause problems in Collies and other herding breed dogs that carry the MDR1 mutation.  We suggest that you link to the Washington State University web site which has a list of drugs that have been researched because information on these drugs changes often.

The most common drugs known to cause neurological signs are listed below.  We suggest that these drugs be avoided completely unless you are absolutely sure the amount to be administered is in the "safe" dosage zone.

Invermectin (antiparasitic agent).

Acepromazine (tranquilizer and pre-anesthetic agent).

Butorphanol (analgesic and pre-anesthetic agent).



Selamectin, milbemycin, and moxidectin (antaparasitic agents).

Vincristine, Vinblastine, Doxorubicin (chemotherapy agents).


Important: Please ensure that your vet is aware of the possible drug sensitivity of your dog.


For more details on these drugs, and others, and the amounts that are recommended to be administered please follow this link to:

Click here to download Victorian Collie Rescues MDR1 listing


Click here for the WASHINGTON STATE UNIVERSITY website


Note: The above infomation has been sourced from the Washington State University website Feb 2010, but due to ongoing research in this field the above information is subject to change at any time, we suggest therefore that you thoroughly research any drugs yourself, and are aware of their side effects before you administer them to your dog.


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