Credelio is a chewable oral tablet for the treatment and prevention of flea infestations and for treatment and control of the American dog tick, black-legged tick, lone star tick, and brown dog tick in dogs. The active ingredient is Lotilaner, which is in the isoxazoline class of flea parasiticides. This medication is given monthly by mouth with a meal. It begins killing fleas within 2 to 4 hours of administration. Credelio is a very safe medication with rare side effects. Vomiting after administration has been reported. Credelio and the other flea preventions that are in the isoxazoline class should be used in caution with pets with known seizure history or neurologic disorders. If any unwanted side effects or changes in behavior or health are detected, this medication should be discontinued and our veterinarians should be notified.