Frequently Asked Questions
What drugs is a dog sensitive to if he/she has the MDR1 mutation?
Does the MDR1 test tell me what breed my dog is?
Does it matter if I send in a blood sample or a cheek swab? Is one better than the other?
MDR1 genotyping requires a minimal amount of the patient’s DNA. The Veterinary Clinical Pharmacology Laboratory has developed techniques for processing either sample type to provide accurate results. We accept both sample types because blood samples tend to be the simplest way for veterinarians to collect DNA samples while cheek swabs tend to be the simplest way for owners to collect DNA samples.
Why do I see medications listed on other websites potential caustion drugs lists but they are not on yours?
The Veterinary Clinical Pharmacology Laboratory lists information about drugs that have been (a) documented to cause adverse reactions in dogs with the MDR1 mutation or (b) strongly suspected to cause adverse reactions in dogs with the MDR1 mutation. We do not list drugs that are potentially toxic to any dog (i.e., drugs in which the toxicity is unrelated to the MDR1 mutation). Many other websites contain inaccurate information and we are not able to control the information posted on these websites.
When will I get my results?
MDR1 genotype tests are run in batches, which begin on each Monday. If your test arrives in time to be included in Monday’s batch, you should receive your results on the Friday of that same week. Any test samples received after Monday morning are included in the next week’s batch.
I submitted my sample under my dog's call name but now I want to change it to the registered name. Can I do that?
No. If you think you may submit these results to an open genetic testing results database, all information must be correct at the time of submission. It cannot be changed at a later date.
Can Collie crosses or other herding breed crosses carry the mutant MDR1 gene and have an adverse reaction to a normal dose of drugs?
Yes, it is less likely in a mixed breed, but still possible. We have found the mutant gene in a Saint Bernard mix that had an adverse drug reaction. The veterinarian did note that each eye was a different color, like some Australian Shepherds.
How old must a dog be before it can be tested?
A puppy can be tested as soon as it is weaned from its mother. There is a small chance that a cheek swab from a nursing puppy would contain enough of the dam’s DNA to generate a false result. If a blood sample is used, a puppy can be tested at any age.
Can mixed breed dogs have the MDR mutation?
YES! We have identified many mixed breed dogs with the MDR1 mutation. Some of them have no resemblance to herding breed dogs. That is why we strongly recommend testing mixed breed dogs for the MDR1 mutation prior to administering any of the “problem drugs”.
I have a mixed breed dog. Will the MDR1 test indicate what breeds my dog is?
The MDR1 test will determine if your dog has the MDR1 mutation, which predisposes dogs to many adverse drug reactions. It is true that the MDR1 mutation has been identified only in herding breed dogs, so if your dog tests positive for the MDR1 mutation, then it is highly likely that your dog has an ancestor that is one of the herding breeds.
What heartworm prevention products can I use if my dog has the MDR1 mutation?
All heartworm products labeled for dogs in the U.S. have been tested in dogs with the MDR1 mutation as required by the FDA and have been found to be safe. However, some of the combination flea+heartworm preventive products (those containing spinosad) should be used cautiously in dogs that are MDR1 mutant/normal because of a risk of serious drug-drug interactions.
My dog has tested positive for the MDR1 mutation. Now that Interceptor is no longer available, what heartworm preventive product should I use for my dog?
Any of the monthly heartworm preventives (administered at the label dose) can be used in dogs with the MDR1 mutation. We recommend avoiding the 6-month or 12-month injectable products and we prefer the single-ingredient products to the multiple ingredient products.
Does it matter if I submit a blood sample or cheek swab sample?
Both sample types contain an adequate quantity of DNA for accurately determining the dog’s MDR1 genotype. We accept both types of samples because one (blood) tends to be more convenient for veterinarians and the other (cheek swabs) tend to be more convenient for dog owners.
Can the MDR1 status of puppies be predicted by the MDR1 status of the sire and dam?
MDR1 Breeding Pair Combinations and Outcomes
|| Normal/Normal Male || Normal/Mutant* Male || Mutant/Mutant Male |
| Normal/Normal Female ||
100% Normal/Normal puppies ||
Normal/Normal and/or Normal/Mutant puppies ||
100% Normal/Mutant puppies |
| Normal/Mutant* Female ||
Normal/Normal and/or Normal/Mutant puppies ||
Any combination of puppies ||
Normal/Mutant and/or Mutant/Mutant puppies |
| Mutant/Mutant Female ||
100% Normal/Mutant puppies ||
Normal/Mutant and/or Mutant/Mutant puppies ||
100% Mutant/Mutant puppies |
*Normal/mutant is the same as mutant/normal and "heterozygote"
Can individuals outside the United States order a test kit?
Yes, we can run samples from any country except Australia , New Zealand or European countries (including Britain). For those countries, please see the links below. If you have questions please contact us at VCPL@vetmed.wsu.edu.
For individuals in Australia and New Zealand, the exclusive licensee for MDR1 genotyping is The Gribbles Group, and they may be contacted at:
Dr. Richard McCoy, PhD
Head Scientist, Molecular Diagnostics
Gribbles Veterinary Pathology
1868 Dandenong Road
Phone: +613 9538 2241
Fax: +613 9538 6778
The Veterinary Clinical Pharmacology Laboratory will test dogs from all European countries except: the United Kingdom, Germany, France, Switzerland, Netherlands and Austria. For individuals in the United Kingdom, Germany, France, Switzerland, Netherlands and Austria, the exclusive licensee for MDR1 genotyping is Genetic Counseling Services, and they may be contacted as listed below.
0252 532 284
Genetic Counseling Services
2182 GR Hillegom