Ivermectin Sensitivity MDR1 (Multi Drug Resistance)

Test Overview:

In certain breeds a mutation on the MDR1 gene (which stands for Multi Drug Resistance 1) makes affected animals sensitive to certain drugs. The first drug that this defect was found to be present for was Ivermectin, used to treat mange and prevent heartworm. Affected dogs suffer seizures when given this drug. It has since been found that the mutation on the MDR1 gene means that the brain is not able to efficiently pump some drugs out of its protected environment the way normal brain vessels do – hence these drugs can enter and build up in the brain tissue, and cause toxic effects such as seizures. A range of drugs are usually pumped out of the brain by the protein pump that the MDR1 gene is responsible for, and so dogs carrying the defective (“mutant”) gene are sensitive to a whole range of drugs. Dogs carrying two copies of the mutant gene are more sensitive to these drugs than those with one copy of the gene. For more details on the drugs involved in this disease, information can be found at Your vet should be aware if your dog is carrying an affected MDR1 gene, or 2 copies of the gene, as the amount of these drugs given needs to be reduced to avoid toxic effects, or alternative drugs used if available. This genetic defect is known to occur quite commonly in a number of breeds, especially Collies, and a DNA test is available to determine if your dog is carrying abnormal MDR1 gene/s or not.


Nervous system / Neurologic - Associated with the brain, spinal cord and nerves


MDR1 on Chromosome 14

Variant Detected:

Deletion 4bp AGAT


Low-Moderate. This disease can cause some discomfort and/or dysfunction in the affected animal. It does not generally affect life expectancy.

Mode of Inheritance:

Autosomal Dominant with Incomplete Penetrance

Research Citation(s):

J Vet Intern Med. 2011 May-Jun;25(3):484-9. [PubMed: 21488961]
Vet Dermatol. 2009 Apr;20(2):111-4. [PubMed: 19171022]
J Vet Pharmcol Ther. 2007 Oct;30(5):482-485. [PubMed: 17803743]
Vet J. 2011 Jul;189(1):67-71. [PubMed: 20655253]
J Vet Diagn Invest. 2012 Jan;24(1):127-34. [PubMed: 22362942]
Pharmacogenetics. 2001 Nov; 11(8):727-33. [PubMed: 11692082]
J Am Vet Med Assoc. 2008 Sep 15;233(6):921-4. [PubMed: 18795852]
Proc Natl Acad Sci U S A. 2004 Aug 10;101(32):11725-30. [PubMed: 15289602]
J Vet Intern Med. 2003 May-Jun;17(3):354-6. [PubMed: 12774979]
Res Vet Sci. 2016 Jun;106:89-92. [PubMed: 27234542]

Associated Breed(s):

Australian Bulldog, Australian Cattle Dog, Australian Cobberdog, Australian Kelpie, Australian Labradoodle , Australian Shepherd, Australian Stumpy Tail Cattle Dog, Black Russian Terrier , Border Collie, Cavoodle, Chinook, Collie Rough, Collie Smooth, Dwarf Poodle, English Shepherd, German Shepherd Dog, Goldendoodle, Groodle, Koolie , Labradoodle , Labradoodle , Labradoodle Retrodoodle , Miniature American Shepherd, Miniature Australian Shepherd, Mixed Breed, Old English Sheepdog , Shetland Sheepdog, Whippet , White Swiss Shepherd,