6 Pack -- Advantage II is a once a month treatments that eliminates fleas and now offers better protection for your cat. The formula is for use only on cats 8 weeks and older and for use only on cats weighing under 5 lbs. This new and improved flea control product eliminates fleas at all of their life stages. The fast-acting formula imidacloprid will kill fleas within 12 hours and re-infesting fleas within 2 hours.