Tape worms

After worming tablets given by the vet made Ozzy vomit on the way home, the next visit he used drops on his neck. I have drops that cover fleas, roundworms and other parasites, but I've only just noticed it doesn't cover tape worms. Something I haven't thought of before. I've known when he has roundworm in the past, he's vomited a furball with live worms in it, and it's a reminder he's overdue his neck drops.

Anyway, lately he's been after food at any opportunity, driving us mad pestering for feeding, and on 3 occasions in 3 days I caught him eating a mouse outside, even after being fed. Then yesterday he vomited on the living room carpet, and I was grossed out to see live tape worm in it.

I dug out some neck drops I bought a while ago for tape worm, and put it on him, he seems more settled today, so I'm hoping it's done it's job, but was wondering what faith you have with this way of treating them, should I take him to the vet for something stronger? And what in particular I should be watching for as an indication that it needs further treatment?

He's around 15 or 16 years old, I don't want to stress him more than necessary. 

Thanks in advance for any feedback.

What was the medication called? I'm not familiar with the drops, but if it was Droncit I would think it should work similarly to their pill form. It's important that he's not re-exposed, or he will get tapeworm again. He could have gotten it from fleas, so it's important to check for those, or from eating the mouse. Can you keep him inside?

That's the name of the drops. And he can't be kept inside, he's too used to going out, he starts going a bit scatty when he wants to go out. He was a rescue cat and was looking after himself for no one knows how long before he was rescued, so he's always had a habit of hunting, and eating what he catches.

I guess I'll just need to keep on top of his medication. I do tend to let it slip, especially through the winter months.