Products like Revolution etc. (selamectin) contain the topical anti-parasite drug selamectin. Revolution is a liquid that is administered once a month at the base of the dog's neck in front of the shoulder blades.
Revolution kills adult fleas, and also prevents flea eggs from hatching. It also kills ear mites, scabies, dog ticks, and prevents heartworm. (Revolution for dogs does not treat intestinal parasites like roundworms, whipworms, or hookworms).