MDR1 GENE - AUSSIE DRUG TOXICITY
It is well known that certain breeds have reactions to certain drugs. It was previously unknown why some
dogs were sensitive and some not. Advances in molecular biology has found the problem to be due to a
mutation in the multi-drug resistant gene (MDR1). This gene encodes a protien, P-glycoprotien, that is
responsible for pumping many drugs and other toxins out of the brain.
Dogs with the mutant gene can not pump some drugs out of the brain as a normal dog would. The result may
be illness possibly requiring an extended hospital stay, or even death. You simply need to use alternative
drugs recommended by you vet that are safe for these breeds.
Infected breeds that have been positively diagnosed include:
Collies (rough and smooth), Shetland Sheepdogs, Austrailian Shepherds (all three sizes), Old English
Sheepdogs, German Shepherds, McNabbs, Long-Haired Whippets & Silken Windhounds and Mix-breeds with
any of the above in their background! As the testing becomes more precise and more breeds are tested it is
expected that more breeds and more drugs may be added to the list. (For example; an Aussie x Golden
Retriever cross has been tested positive - positive, which means that the Golden had to have had the gene
also! Story published on the WA State U site at )
50% of the Standard Aussies and 50% of Mini-Aussies have at least one copy of the gene.
How do I know if my dog has the MDR1 mutation?
If your dog has already reacted to one of these drugs, it has the mutation. However, reactions can be so
dangerous to your dog it is advisable to have the dog tested so you know whether it is sensitive before it
receives any of the listed drugs.
What do the MDR1 test results mean?
This is a DNA mutation test. It will determine whether or not a dog has the MDR1 mutation and, if it does,
whether it has one copy or two. The test report will provide you with the genotype for your dog, generally
listed as Normal/Normal, Normal/Mutant or Mutant/Mutant.
Dogs with even one copy of the mutation should be considered sensitive to listed drugs. If your dog carries
the mutation, provide a copy of the test results and a copy of the listed drugs to every veterinarian who treats
your dog and let them know your dog cannot have those drugs.
What dogs should be tested and how often?
Since this is a DNA test, a dog only needs to be tested once. Due to the high frequency of the mutation in the
breed and the variety of drugs to which dogs with the mutation can react, all dogs, including rescues of
unknown parentage and Aussie-mixes should be tested. Their lives could depend on it.
The only exception is as follows: If both parents of a dog have tested Normal/Normal, they cannot pass on
the gene and their offspring will not need to be tested. However, if a Normal/Normal dog is bred to one of
unknown status or one that has even a single copy of the mutation, the offspring must be tested.
How do I get the test done?
For those in North America, The test is available through Washington State University. Information can be
found on their website:
In Europe the test is available through Genetic Counseling Services in the Netherlands:
In Australia, Genetic Technologies Ltd. and Gribbles Veterinary Pathology offer the test.
Below is a list of drugs that have been documented, or are strongly suspected to cause problems in dogs
with MDR1 Gene Mutation:
*IVERMECTIN (antiparasitic agent)
LOPERAMIDE (Imodium, over the counter human anti-diarrhea agent)
DOXORUBICIN (anti-cancer agent)
VINCRISTINE (anti-cancer agent)
VINBLASTINE (anti-cancer agent)
CYCLOSPORIN (immunosuppressive agent)
DIGOXIN (heart drug)
BUTAPHONAL (pain control)