While I am, in no way an expert on this, I would be very careful in the wording of these references. If they are generic enough, then it should be okay, but if there are any specific references to medical school or aptitude to be a physician, I would be very wary. In addition, the best reference letters have specific examples as to why you would be well suited to a field. Re-using letters kind-of negates this possibility. Hope this helps!