I'm sorry to hear that they have tapeworm. I was also going to say that Drontal pills work very well. My Sky had them shortly after I adopted him. He had been deflead but not dewormed before I adopted him and apparently must've swallowed a flea. Since he's a large cat, I had to give him two doses of it. I think it was about 2-3 weeks apart. Even though my cats are indoor only, I've been using advantage every month for many years now and I've never ever had any more flea problems or tapeworm problems either. Good luck.