I'm sorry to hear that Frisky has fleas. Even though my cats are indoor only, I use advantage every month because I had a flea problem several years ago. Since then all of my cats have been fine. Since some fleas can carry tapeworms, you may also want to have the vet give him some drontal pills so that he won't get tapeworms. My newest furkid Sky had fleas before I adopted him and ended up with tapeworms. Good luck and please keep us updated.