Please make sure your cat has not got an immune deficiency before you use Advantage or similar products.
My 8 year old cat who had not been to the vets before had a very bad attack of fleas for the firast time in 8 years and I used Advantage on her.
She died and a blood test showed that she had Cat Aids but was not ill with it until the Advantage compromised her immune system.
Thats why it affects only a few cats and dogs.
If cats get bad attacks of fleas it may be that their immune system is down for one reason or another,get a blood test first. Do not learn the hard way like i did.