here is what we do, you can get capstar from your vet.
To treat a flea- infested cat, a 3-step approach is recommended:
1. Treat with Capstar, a pill which kills fleas within an hour (lasts
only 24 hr). We use dog size Capstar (>25 lb). The dose is ¼ pill for
adults, and 1/8 pill for kittens.
2. Wait 30-60 minutes, then bathe the cat using a mild shampoo (NOT a “
flea” shampoo) to remove dead fleas and larvae.
3. Wait 24 hrs, then treat with a topical flea treatment- Frontline or
Advantage (must wait after bathing for the cat’s skin oils to be
replenished)