we use generic frontline on our birds, cats, and goats. It works well. I think there is one kind out there that says not for cats so I have to check and make sure every time i get some that I get the kind that can be used on dogs but also has the same ingredients as the cat one. The over 100 pound dog package that was mentioned above is the cheapest way to get the most frontline. Another thing to consider is timing of the purchase, the stuff is much cheaper come October - January.