Multidrug Resistance 1 is a genetic mutation in a protein that transports drugs out of the brain. This mutation causes sensitivity to certain drugs, including ivermectin and loperamide. Because of this lack of drug clearance from the brain, affected cats experience neurological symptoms such as ataxia or even death. The MDR1 mutation has currently been identified in the breeds listed below; however, the test can be conducted in any breed.
