Advantage Purple 4 Pack for Large Cats or Rabbits More Than 9 Pounds (4kg) Advantage is the fast, easy to use flea control for your pet. Is effective against fleas all month long Kills fleas fast: Advantage kills 100% of existing fleas within 12 hours Keeps killing fleas within 20 minutes of contact. Can be used on kittens over the age of 8 weeks