Advantage II is the successor of Advantage and comes with three new ingredients, all insect neurotoxins. Quite obviously, the new formula is more effective at getting rid of the pests than the original Advantage. The old formula was rated to kill adult fleas within 12 hours of application; however, the drawback of the Advantage flea medicine is that it only works on adult fleas and now on flea larvae or flea eggs. On the other hand, Advantage II for dogs also starts killing fleas 12 hours after the application. However, the new formulation comes with additional protection against fleas. It stops the flea life cycle as it stops larvae from developing. This means that your dog or cat gets complete flea control for 30 days at multiple flea life stages.