Otherwise healthy cats with a genetic MDR1 mutation can develop severe neurologic effects after treatment with certain prescribed drugs. The mutation disrupts the function of P-glycoprotein, which normally clears harmful substances from the body, including some drug byproducts. These cats cannot safely process drugs that are manageable for other cats.

Tests are available to identify cats with an MDR1 mutation. But now, a second test has been developed to identify which drugs rely on P-glycoprotein for processing. That way, veterinarians can avoid prescribing these drugs to cats with the mutation.

Even genetically normal cats could benefit, since P-glycoprotein deficiency can result when two or more drugs using P-glycoprotein processing compete for clearance if given at the same time.