What flea medication are you using? Are you referring to the Pred? The Pred will treat the inflammation your cats are experiencing but it will do nothing in killing and ridding your cats of fleas.

Unfortunately, there's no way to keep fleas from biting. If you don't have dogs bringing the fleas in your home then you are most likely bringing them in on your clothing. It sounds like your have a flea infestation in your home so spend your money on treating your yard and house, and in the meantime use one of the treatments I mentioned above on your cats.

Here is a link that might be useful: Controlling fleas

Garlic isn't good for cats.

Are you sure it's a flea problem? Are you actually seeing fleas or flea dander on the cats?

If so, the best approach is to find the source of the fleas and eradicate them. If you don't get rid of the fleas the problem is going to get out of hand because they multiply like crazy! If they were recently adopted they very well may have come with fleas which have now deposited into your house. I'd concentrate my efforts on the house (or yard like the link above suggests).

Last year mine came in with fleas.I hadn't flea treated them because we never had a flea issue before. I was fortunate to catch it early on before they got out of control. I didn't want to bomb with chemicals. I used PET GRADE Diatomaceous Earth. It comes in a powder form. It only cost about $15 a bag. I'd give the carpet a really good vacuuming and then sprinkled it on and let it sit to catch any eggs that were ready to hatch. I repeated the process daily. You can even sprinkle this stuff on your furniture. Vacuum, vacuum, vacuum. A lot of housework but it took care of the problem. I hate using the pesticides but the cats now get an Advantage treatment each month while the weather is warm.

Here is a link that might be useful: garlic

I think the last comment is a good one to consider... do you see evidence of fleas? Put your cat on a white piece of paper and rub its fur backwards for a few minutes... do you see flea dirt (small, black, curled bits of digested blood)? If not, probably your cat does NOT have fleas, but is allergic to something else (not an unusual situation). Cats may LOOK like they have fleas they way the bite and scratch at themselves, but can easily be allergic to food items, house dust mites, pollens (all indoor air has pretty much the same pollens as outdoor air unless you have an incredible filtration system in your house), etc.

But let's say you were still battling fleas.. .you should be able to rid them with just about any of the good flea products available today in just a few months, unless you have a weak link (pets that go in and out, and bring things back in with them).

And even if you did get rid of your flea problem, once a cat has the allergy, they can keep on itching for months afterwards (like we do when we contact poison ivy... we itch for weeks to come... and longer if we keep scratching at our itchy spots, even though the poison ivy is long gone). So you may still need to treat them symptomatically for itching despite no more fleas.

PS. As mentioned, garlic is toxic for cats... and has been shown over and over and over again to be useless in its ability to deter fleas... brewers yeast (not brewster yeast) is also useless, but at least is not toxic.