I would get 100% positive advice from a Vet about dosage guides. Advantage for dogs IS safe to use on cats - see if you can get a low mill-age syringe from the vets or a chemist (say 1ml) and use that.

There is a product from Bayer that should NEVER be used on cats however, and that is Advantix - be careful of the product you purchase. Luckily Advantix (here in NZ anyway) has something like 33 warnings on EACH box saying DO NOT USE ON CATS.