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Canine MDR1 Mutation
MDR1 Veterinary Fact Sheet
Info Center
The multi-drug resistance gene (MDR1) encodes P-glycoprotein, a protein that functions as a drug-transport pump across cell membranes. A lack of P-glycoprotein means certain drugs cannot be absorbed, distributed or metabolized normally (particularly affecting the brain). Dogs with the MDR1 genetic mutation have a P-glycoprotein deficiency and are extremely susceptible to toxicosis from many common drugs. Affected Breeds
The MDR1 mutation has been documented in many herding breeds and some sight hounds. The breeds
affected by the MDR1 mutation (frequency %) is shown below.
Approximate Frequency
MDR1 Mutation Test
The Veterinary Clinical Pharmacology Laboratory (VCPL) at Washington State University has developed
a commercially available test for the MDR1 mutation. Any dog of any breed can be tested via DNA
collected from a cheek swab. Results are reported as homozygous for the normal MDR1 allele
(normal/normal), heterozygous (mutant/normal), or homozygous for the mutant MDR1 allele
(mutant/mutant). Dogs carrying the mutant gene or dogs from affected breeds that have not been
tested for the mutation should not be given any of the MDR1 problem drugs – the exception
being heartworm preventative, which is deemed safe when administered in the proper dosage.
Order a testing kit by contacting the Veterinary Clinical Pharmacology Laboratory at Washington
State University:or by phone at 509-335-3745.
Problem Drugs
The most serious adverse drug reactions involve several antiparasitic agents (ivermectin, milbemycin,
and related drugs), the over-the-counter antidiarrheal agent loperamide (Imodium), and several
anticancer drugs (vincristine, doxorubicin, and others). These drug sensitivities result from a mutation in
the multidrug resistance gene (MDR1 gene).
For the most up-to-date version of the MDR1 Problem Drug List, visit the WSU Problem Drug List website. BusterAlert is a project of Mini Aussie Rescue & Support (MARS) www.miniaussierescue.org
BusterAlert.org
MDR1 Problem Drugs List
Canine MDR1 Mutation
Info Center
with North American Brand & Trade Names
Dogs who test as having a mutated MDR1 gene OR dogs from affected breeds
who have not been tested for the mutation should avoid these drugs.
Drug names in bold are the generic drugs identified as problems by the MDR1 researchers. Below each generic drug is a list of some of the synonyms, brand, and trade names for the generic drug provided by BusterAlert.org. More drugs are likely to be added as MDR1 research progresses. Drugs Affected by the MDR1 Gene Mutation
Acepromazine
Ivermectin
Loperamide
Milbemycin
Moxidectin
Ribampin
Butorphanol
Selamectin
Vinblastine
Doxorubicin
Vincristine
Erythromycin
This list is not inclusive. For more information and updates on the Problem Drug List, see
To find more generic and brand names of these drugs, see
BusterAlert is a project of Mini Aussie Rescue & Support (MARS) www.miniaussierescue.org

Source: http://miniaussierescue.org/BusterAlert/MDR1%20Problem%20Drug%20Info%20Sheet.pdf