When I brought my kitties home from the Animal Shelter we had a horrible flea infestation!
On top of that they both ended up with tape worms, which are caused by fleas. So in order to get rid of the tape worms we had to be rid of the fleas.
I bought carpet powder - the stuff smelled HORRIBLE, it was expensive and it didn't work.
I tried several other brands of "Spot treatment" and nothing worked. The cats seemed to scratch less for about a week, but shortly after, I would be finding flea eggs in their bedding again!
Finally my vet recommended Frontline. While it is a bit spendy compared to some of the others it is worth EVERY penny! The cats went crazy for a day or two, because the fleas become more active from the treatment. After that, the scratching stopped completely! No fleas, no larvae, no eggs!
I'll never buy anything but Frontline again!