Exactly as James A said, if you're going to apply for such a competitive course like Medicine, go all out for Medicine. Most people who I know who got 4 Medicine rejections didn't accept their 5th choice - unless it provides an alternative route into Medicine. For example some courses allow you to apply after just one year in that 'other' course.
If the admissions team sense at all that you're not fully committed, you'll never get any offers.
So what I've said to students applying for Medicine/Dentistry/Vet for 2013 is just focus on that. Get your application as perfect as you can, then you'll have a great chance of getting offers(s). And if you want it so much, you'd never consider a different course and you'd reapply next year.
Good luck!