My story is a bit different, as I am going from being a graduate student to becoming a pharmacy student. I'm finishing with my PhD first (hopefully... depending on how my thesis work goes!), but there was another grad student at my school that stopped with a Masters to go into a PharmD program. He successfully got in with little to no problems, as far as I know.
So, I don't think it's a problem to switch programs, as long as you did well in the pre-reqs and the PCATs and have a good explanation as to why you want to switch. Provided you haven't also quit a dental program and a PhD program before you went to med school... ;-)