I might suggest something besides Ivermectin, I gave it to a dog and had fatal results. I'm also not the only one I've heard that this has happened to. I reccomend Drontal tabs. They work great and I've never had any bad side effects from them.
Well that changes things a bit. Ivermectin does not treat tapeworms, it treats lots of things but thats one that it doesnt. You will have to use something with prazaiquantel or ask your vet what they might have. The reason that the horse wormers started making prazi/ivermectin combos a few years ago is to address tape worms. If you ask your local pet supply store you are looking for Tape Worm Tabs they will know what you are talking about, there a few different brands but most are comparable to each other in terms of price.