Mulitdrug Resistance Gene: MDR1 Ivermectin Sensitivity (UK Samples Only)

This test is offered by the Animal Health Trust under licence from Washington State University, Pullman, WA, USA. Please note that under the terms of this licence we can only accept samples from addresses with in the United Kingdom.

What is it?

The MDR1 mutation causes dogs to have sensitivity to the anti-parasitic agent ivermectin and a number of other drugs.
This mutation affects the gene for P-glycoprotein, which is involved in drug transport across the blood-brain barrier and drug excretion. Loss of functionality of P-Glycoprotein, allows build-up of the drug in the brain leading to potentially fatal neurotoxicity.

Symptoms of ivermectin toxicity can include: Lethargy, drooling, Tremors, disorientation and blindness.

Affected Breeds

Some breed affected by the MDR1 ivermectin mutation
This mutation and the related ivermectin sensitivity have been found to affect several breeds, see the list below.

This mutation is common in Collies and dogs from herding breeds Such as: Collie, Shetland Sheepdog, Miniature Australian Shepherd, Australian Shepherd, Old English Sheepdog, English Shepherd, White Swiss Shepherd, and Border Collies.

Mixed/cross breed dogs may have some of the many breeds affected by this mutation in their ancestry and so can be affected by the mutation also. It is recommended that these dogs are also tested.


How is the disease inherited?

The disorder appears to show an autosomal recessive mode of inheritance.

Individuals with one copy of the mutation and one copy of the normal gene, called carriers, may show some sensitivity as a result of the mutation. These animals will pass the mutation onto around half of their offspring.

When two carriers are mated, 25% (on average) of the offspring may be affected by the disease, 25% will likely be clear and the remaining 50% will themselves be carriers.

Results identify your dog as belonging to one of three categories.  In all cases the terms ‘normal’ and ‘mutation’ refer to the position in the DNA where the MDR1 mutation is located. iIt is not possible to learn anything about any other region of DNA or the breed of your dog from this test.

This test only detects this specific mutation; there maybe additional forms of drug sensitivity that are caused by different mutations. These cannot be detected by this test.


CLEAR of the Multi-Drug Resistance (mdr1) mutation: These dogs have two normal copies of DNA. Clear dogs will not show drug sensitivity as a result of the mdr1 mutation.

ONE COPY of the Multi-Drug Resistance (mdr1) mutation: These dogs have one copy of the mdr1 mutation and one normal copy of DNA. These dogs may show some drug sensitivity as a result of the mdr1 mutation and will pass the mutation on to approximately 50% of their offspring.

TWO COPIES of the Multi-Drug Resistance (mdr1) mutation: These dogs have two copies of the mdr1 mutation and will show drug sensitivity.

Please note that we cannot exclude the possibility that you dog could show drug sensitivities due to other mutations that are not detected by this test.

What should you do if your dog is genetically affected?

You should inform your vet of your dogs result. This will allow them to ensure that the best treatment choices are made for your dog.

Related drugs

The following drugs have been found to cause problems in dogs with the MDR1 mutation: Ivermectin, Selamectin, Milbemycin, Moxidectin, Loperamide, acepromazine, Butorphanol and some chemotherapy agents.

Please note that this is not an exhaustive list, new discoveries occur all the time. Check with your vet before treatment

For more information please contact us and we’ll be happy to deal with your enquiry.