Katrina L. Mealey, DVM, Ph.D., DACVIM, DACVCP, and her team have identified cats with the MDR1 genetic mutation are at risk of severe adverse reactions to the active ingredient in some top-selling parasite preventatives for felines. The ingredient, eprinomectin, appears safe and effective for most cats except those with the MDR1 gene mutation.
Genetic testing is the only reliable way to know if a cat has the MDR1 mutation. Mealey’s team recommends testing for all cats, preferably when they are kittens.
Source: WSU Insider, March 28, 2024. Link. Genetically affected cats lack a protective mechanism that prevents certain drugs entering the brain and causing serious neurological toxicity including eprinomectin.