Half a million cats in the U.S. could be at risk of a severe or even deadly neurological reaction to an ingredient in parasite medication.
A new study conducted by researchers at Washington State University's (WSU) Program for Individualized Medicine assessed the ingredient called eprinomectin, which is found in various popular medications that protect against pests such as fleas and ticks.
Although the ingredient appears safe, the researchers found that cats with a specific genetic mutation known as MDR1 lack a mechanism that prevents the ingredient from entering the brain. If it enters the brain, it can cause "serious neurological toxicity" the researchers state.
Cats with the mutation may experience a variety of adverse symptoms, including tremors, paralysis, and a loss of coordination. Some cats were also unable to retract their tongue for days or weeks after being given the medication.
"Almost every week we receive reports about someone's pet cat having serious reactions to eprinomectin. This is not an issue with the drug itself—the problem lies in the genes of 1 percent of cats. That is a sizable number considering there are over 60 million pet cats in the U.S., and we're trying to increase general awareness of these risks," Katrina Mealey, a WSU veterinarian and pharmacologist who led the research, said in a statement.
To reach their findings, Mealey and colleagues reviewed the records of 33 cats who had become extremely ill or died after being exposed to the ingredient. The research came after they spotted an uptick in neurological side effects in cats after a marketing campaign for products containing the ingredient in the U.S.
In 14 cases of these 33, there was "no other reasonable cause" identified for their severe reactions. Out of these 14 cats, eight had the MDR1 mutation. Three of these cats died.
"While this appears like a small number of cases, we consistently receive new reports. If this were happening in human patients, federal agencies would be issuing regulatory actions immediately," Mealey continued in the statement.
"The results indicate cats with the MDR1 mutation are at high risk for experiencing serious adverse effects from products containing eprinomectin, and they should not be treated with these products."
The new findings were published in a study in the Journal of Veterinary Pharmacology and Therapeutics.
The researchers hope that the study will lead to warning labels being put on products that contain the ingredient.
Genetic testing for the mutation will be the only way to determine whether a cat is at risk. Mealey recommends that all cats be tested, preferably as kittens.
"Pet owners really should be aware of the risk to their pets. Based on the data in this study, I hope the FDA [Food and Drug Administration] acts to conduct a timely review of the current labeling standards and adopts the modifications necessary to protect the health and lives of cats with the feline MDR1 mutation treated with this product," Mealey said.
"I recommend the test for all cats, preferably when they are kittens. If your veterinarian knows your pet has the MDR1 mutation, he or she can ensure only safe medications and doses are administered."
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