Frontline Plus for Cats (3 pack - green) is a topical spot-on application with a rapid onset of action designed for the treatment and prevention of flea infestation and biting lice on cats and kittens. Frontline Plus kills re-infestations with adult fleas for at least one month and also prevents the development of flea eggs, larvae and pupae produced by any adult fleas acquired for up to six weeks after treatment.