I consulted with my vet and decided to try Program tabs (not the yucky liquid stuff!). Turns out that 1/4 of the largest dog Program contains the amount of lufenuron a medication that would work to prevent future fleas for a small cat. This is a monthly dose. (Larger cats would need 1/2 tab.) The trick is that the medication is not dispersed uniformly throughout the tablet, probably to prevent this 'off-label' use. So, it's a little tedious, but you have to crush the tablet, then divide the powder into two to four doses. I put those in pieces of waxed paper. Then, onsite, mix a dose with canned food and try to get one of those into most of the cats. My vet explained that each cat then acts as a flea deterrent by leaving a little residue of the medication on the ground where they hang out. (Not the scientific explanation, I know!) Anyway, about two weeks after we used the Program for the first time, we gave everybody we could a Capstar, also crushed, in canned food. We saw a great difference there, even within those first couple of weeks!
Email me if you would like the dosage charts for Program used for dogs and cats. The 'contact me' link is on the 'Toys' page.