Bayer Advantage II for Cats is a waterproof, once-a-month topical flea prevention treatment for cats and kittens over 8 weeks old. Contains Imidacloprid, an adulticide, and Pyriproxyfen, an insect growth regulator. Advantage II for Cats controls existing flea infestations on your cat and prevents further infestations. Kills all flea life stages; kills fleas within 12 hours of application. Prevents further infestations for up to 4 weeks. Purple: for Large cats over 9 lbs.