What is afoxolaner?

Afloxolaner was released by Merial Animal Health in 2014 as a beef-flavored chewable prescription medication called "Nexgard®."  A related product called "Nexgard Spectra®" is available in Europe. Nexgard Spectra combines afoxolaner and milbemycin, an anti-worm medicine, so as to provide nearly total parasite protection in one product but this version of Nexgard is not presently available in the U.S.

A valid patient-doctor relationship is required to obtain a prescription for afoxolaner. Nexgard kills fleas and ticks only and has no activity against intestinal worms or heartworm. There are four ticks of concern in the U.S. (see our tick product comparison chart for more details) and afoxolaner will kill all of them. As for fleas, afloxolaner kills fleas before they are able to lay eggs so that a flea sterilizer is not necessary in the tablet.

Side Effects

The possible side effects reported include nausea/vomiting (4% of dogs), diarrhea (3% of dogs) dandruffy coat (3% of dogs), lethargy (less than 2% of dogs) and appetite loss (less than 2% of dogs). Most dogs that exhibited one of these side effects only exhibited them after the first dose and not with subsequent doses.

If a dog vomits within 2 hours of administration of a Nexgard tablet, a new tablet should be given. If vomiting occurs after 2 hours, re-dosing is not necessary.

Environmental Toxicity 

Little has been published yet regarding the environmental toxicity of afoxolaner. Its use in dogs as recommended is unlikely to pose a risk for the environment, and for this reason no environmental studies have been carried out for the approval of its use on dogs.

Based on its mode of action it must be assumed that it is highly toxic to both aquatic and terrestrial arthropods (insects, ticks, spiders, crustaceans, etc.).