How often and how much Zentel for my 5-month-old kittens?

How much the kittens need to get of the Zentel depends on their weight. The dosing instructions should be on the bottle, and I would follow that. It is correct you need to deworming them every two weeks in the start. That is because it takes at least two dose of the medication given two weeks apart in order to kill all the worms. The first dose kills the adults present, while the second dose kills the ones that had no yet hatched at the time of the first treatment. I would give your kittens two doses two weeks apart, and then I would give it to them monthly until they are six months of age. After that, they can get it every three months. Good luck, I hope this helps!