I've worked in pharma for years though not as a sales rep. The usual requirements for a sales rep is a bachelors degree and 2 years of pharma or at least business to business sales with a good track record. There are opportunities for students and new graduates however. You can look into internships, which can require simply that you be a freshman or sophomore enrolled in a 4-year program. There are also internships for juniors and seniors (they usually want intern or coop experience, though). There are also fast track programs for students who are seniors or have already earned their bachelors and have a GPA of 3.0 or better. These are challenging programs that teach you everything about sales and marketing. My experience is at Johnson & Johnson but other pharmaceutical companies have these kinds of programs too.
Here is a link for J&J. Read through the info on their site. They happen to have several internships right now.