As the weather gets warmer we are now on the lookout for the reemergence of large numbers of fleas and ticks. For the last few years pet owners have been using the oral products in the isoxazoline class (Bravecto, Nexgard, Simparica, and Credelio). These drugs have been extremely successful worldwide with minimal side effects. There has never been any class of drug so successful for external parasites especially for fleas. This is great as fleas and ticks have become more and more prevalent in recent years.
In December the U.S. Food and Drug Administration (FDA) announced new label requirements for this class of drug due to the potential for adverse neurological issues such as muscle tremors, weakness, and seizures. This label change was instituted from the FDA looking at the Adverse Drug Events reports (ADE). These are extremely rare events if you look at the report. For example, Bravecto, manufactured by Merck has 170 studies behind it and has sold over 100 million doses in 85 countries. Only about 25,000 total ADEs have been reported for Bravecto and we do not know how many of these events were actually concerning neurological issues. Nexgard, a Merial product, is used in over 100 countries with more than 200 million doses sold worldwide. The ADEs for Nexgard that have been reported to the FDA are about 24,000 cases. Merial has reported that clinical side effects are extremely rare with one case per 10,000 doses.
Obviously, we as veterinarians are always concerned when we hear of these adverse reaction reports especially when there is the potential for seizure activity. It is always wise to discuss your dog’s particular risk with your veterinarian who knows your dog’s history. One thing for sure is that the risk of flea/tick borne disease is more serious and more likely than the risk of seizures in an otherwise normal dog.