Ivermectin Sensitivity MDR1 - IVM



IVM is a hypersensitivity to the drug Ivermectin, in affected dogs the drug and other toxins cannot be removed from the brain and surrounding tissue, resulting in the accumulation of toxins and can lead to adverse neurological affects. Ivermectin is a commonly used heartworm prevention drug; a mutation in the MDR1 gene in dogs prevents the production of a transport protein, which removes the drug and toxins from the brain and tissues. The resulting accumulation from this failure to detoxify the brain and tissues often results in severe neurological affects such as hyper-salivation, ataxia, blindness, coma, respiratory arrest and death. Unfortunately this sensitivity is not only restricted to Ivermectin, but many preventative canine drugs, it is essential that owners be aware if their dog is IVM sensitive as many affected dogs require as little as 1/200th of the dose to cause fatal toxicity in unaffected dogs.

Severity - 5

IVM has an extreme degree of severity as it can cause immediate death, particularly if the owner/vet is unaware that the dog is affected.


A dog sensitive to Ivermectin will show no signs until given the drug, something as routine as a 6-month heartworm injection has be linked to the accidental and immediate death of numerous dogs.

It is important that testing for this sensitivity is carried out early, as although a dog may show no adverse reaction to the administration of drugs, they may still produce affected offspring if they themselves are carriers of the disease.

Genetic Testing

Animal Network provides a DNA test that determines the genetic predisposition to IVM.

Ivermectin Sensitivity is an autosomal recessive disease. A recessive phenotype (trait or disease) will only be expressed when two copies of the recessive gene variant are present. A direct gene test can detect whether a dog is clear, carrier or is affected by the disease.

A dog with two copies of the recessive gene variant is affected, they will express the phenotype and will pass a copy of the gene variant onto their offspring 100% of the time. A dog with one copy of the recessive gene variant is a carrier, they do not express the phenotype themselves, however they are will pass the gene variant onto their offspring 50% of the time. A dog that has does not have any copies of the recessive gene variant is clear, and will never produce affected offspring.

For an explanation of possible genetic status of offspring please refer to our fact sheet on Breeding strategies. ORDER A TEST

Breeds Affected

Australian Shepherd
Border Collie
White Shepherd
Collie (Rough)
Old English Sheepdog
Shetland Sheepdog

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