I use the Advocate as well, it is a Prescription On Medication, (POM), relatively expensive, BUT, it does heartworm, earmites, parasitic mange, fleas, ticks and other worms as well and then a three monthly dose of Milbumax takes care of any other nasties. In my opinion well worth the expense.
PS. It is also a lot easier to put a pipette of stuff on the back of the neck than it is to hold/wrap a cat still to administer the ear drops and then hold the cat on spread newspaper while your cat shakes and scratches his ears while you are trying to rub it down the ear canal and loads of brown earwax flies out in all directions.
