Kimberley, the Petalcleanse isnt a spray (or it wasnt when I was using it) its a lotion in quite a large bottle, so it should last you a fair old while. All you have to do with it is put some onto a cloth and wipe the cat all over with the cloth, then towel dry - blotting, not rubbing. A bonus is that the cats coat looks and feels lovely afterwards too! I don't think it would interefere with the Frontline which you put on the skin not the fur.