What Is The Best Flea And Tick Medicine For Cats Sep 27, 2022 · Petsradar’s Pick Of The Best Flea Treatments For Cats. This spot-on treatment contains fipronil, an insecticide, and -methoprene, which prevents the development of flea eggs and larvae. Fipronil accumulates in the skin and rapidly kills fleas when they hop onto your pet. This product is effective for 4 weeks, and it should not be used in ...