On Thursday 9/20/18, the Food and Drug Administration Center for Veterinary Medicine (FDA CVM) issued an alert for pet owners about the isoxazoline class of drugs (including Bravecto, Nexgard, Simparica, and Credelio). According to the alert, the FDA has been monitoring post-marketing data, which indicates that some animals have experienced seizures, tremors, and ataxia after taking these products. Further, the FDA is working with the drug manufacturers to update each product’s labeling to “highlight neurologic events because these events were seen consistently across the isoxazoline class of products.”
This statement in the alert caught my eye:
“Although FDA scientists carefully evaluate an animal drug prior to approval, there is the potential for new information to emerge after marketing, when the product is used in a much larger population. In the first three years after approval, the FDA pays particularly close attention to adverse event reports, looking for any safety information that may emerge.”
In July 2018, the Proceedings of the National Academy of Sciences (PNAS), published “Repurposing isoxazoline veterinary drugs for control of vector-borne human diseases.” The authors propose using isoxazoline drugs in the human population to control the mosquito and sand fly populations, thereby reducing incidence of diseases such as malaria and Zika virus.
My question from the very beginning has been shouldn’t we understand why certain animals have neurologic (and other) adverse events after taking an isoxazoline drug? What is the mechanism of action? I am still asking this question of my veterinary colleagues. The question is even more relevant prior to using these drugs in humans.