Em---I used the prescription Revolution. We got infested terribly here when I brought in a 3 week old starving cat. She was half dead. One day I got 40 critters off her 7 ounces of body weight.
My rugs furniture and bedding had to be treated, with Knockout. But the animals were relieved almost immediately.
But the fleas are gone.My two old chubby cats are flea free again. The kitten, too. And so am I.