What is the difference between Advantage and Advantage II?
The main differences between Advantage and Advantage II for cats is that the original Advantage formula did not kill all stages of the flea life cycle. The new formula in Advantage II also kills the flea eggs and larvae. Advantage II contains imidacloprid and pyriproxyfen, which is an IGR or insect growth regulator. The pyriproxyfen is the chemical which prevents the growth of new flea eggs and larvae.
The original Advantage (Advantage 18 or sometimes called Advantage I) does not contain these ingredients and will not work as well to stop fleas on your cats. Additionally, fleas are evolving to be more resistant to flea medications which requires new formulas to effectively fight the fleas.
You want to make sure to get the newest formulas, or the old stuff may not even have any effect on your flea problem.
Larger cats require more strength to kill all of the fleas. Be sure to pick the Advantage II that corresponds to your cat’s weight.
Where to buy Advantage & Which one to get
If you have larger cats 9 pounds or over, then Bayer Advantage II Purple 6-Month Flea Control for Cats 9+ lbs. is the cheapest Advantage II price available anywhere and best bang for your buck. Its 6 doses and even cheaper than the 4 dose pack at Walmart! Don’t be fooled by those sellers on ebay with the Advantage kits. They are using Advantage for dogs which is a different formula and can result in serious adverse effects for your cat, possibly even death. There’s also the Bayer Advantage II Purple 4-Month supply for even cheaper.
If you have a smaller cat under 9lbs, then you’ll want Bayer Advantage II Orange 4-Month Flea Control for Cats 5-9 lbs.