Combiva II for Dogs and Puppies, 11-20 lbs, by Combiva Effectively kills adult fleas and prevents further re-infestation on dogs over 7 weeks of age weighing at least 3 pounds Waterproof after application, and kills re-infesting fleas within 2 hours Breaks the flea life cycle and prevents flea eggs and larvae from developing into adult fleas Effective Once a month flea protection