Depends on the school but you have to get into the med school first before being considered for the business school
For most schools, students good enough to get into the med school are also good enough to get into the business school as well because they have the EC's, GPA, and test taking skills needed to to so (think most state schools). However, I can imagine this being more difficult at places like Wharton or Harvard Business School which really seem to attract the cream of the crop and where a good med school CV might not necessarily be good enough.