Frontline For Dog And Puppies 11-22Lb 6Pk is help to kill fleas and Larvae within 24 to 48 hours. It breaks the parasite life cycle, thus preventing them from laying eggs and reproducing. It is applied to the back of the neck on cats and between the shoulder blades on dogs. It spreads naturally on the skin surface at the hair root level, aided by body movement to provide whole body coverage.