What is MDR1?
MDR1 is a shortening for the "Multi Drug Resistance 1" gene, which is responsible for preventing certain chemicals and microscopic objects from passing through the bloodstream into neural tissue and aiding in their elimination.
Some dogs have a mutation in the MDR1 gene which allows the drug to penetrate the brain causing sensitivity and toxic reactions. Some problematic drugs are common veterinary treatments - the most widely known of which is Ivermectin. MDR1 sensitivity is sometimes referred to as "Ivermectin sensitivity" for this reason, although there are a number of medications known and suspected to cause toxicity. In dogs with the mutation alternative drugs should be used as they are subject to toxicity which can result in death at much lower doses than non-affected dogs. E.G. ivermectin toxicity may occur at as little as 1/200th of the dose.
MDR1 (or "Multi Drug Resistance 1" gene) is something all Aussie owners should be aware of. ASCV MDR1 Brochure