You don't mention your location, but, in the US, medicine is a completely different discipline than nursing, and there is no way to "add in" an MD degree within nursing education. One applies to and gets accepted to medical school, which is entirely separate and different from nursing school
. Nurses are just as welcome as anyone else to apply to medical school, but there is no special preference or advantage for nurses. The prerequisites for med school are different from nursing school, as Goingthere noted, plus one must have an undergraduate degree (medical schools
are graduate programs). In the US, medical school is four years of very rigorous full-time study, followed by several years of residency (the length of residency training varies depending on the specialty chosen). This would all be in addition to nursing school, if we are speaking of a nurse wishing to become a physician.