We had to deal with kitty acne with our old orange boy Valentine. After we switched to a ceramic dish, it took a while for the lesions on his chin to clear up. Just keep treating him with the medicine and give him time. Also, you might want to make sure that his water dish is cleaned regularly, and make sure it's sort of "flat" so he doesn't have to put his face all the way into the bowl.
Best wishes for your furbaby!