Frontline Plus for dogs every four weeks helps protect your dogs from fleas and ticks. Its technology stops flea eggs from hatching in your home. Frontline Plus Spot On Medium Dog is formulated with two tough killing ingredients; fipronil, which kills adult fleas and ticks and the added extra benefit of (S)-methoprene which attacks flea eggs and larvae. They work together to kill all month long, breaking flea life cycles and also destroying the next generation of flea eggs and larvae.