MD/PhD course requirements are the same as the MD programs, at least at all the schools I've looked at. The only exception is if you want to do bioengineering (or some other non-traditional PhD or you're applying to Harvard HST), in which case you need to fulfill the engineering requirements as well which would necessitate calc based physics along with some other courses like linear algebra and diff.eq. You will also usually need to take the GRE in addition to the MCAT. However, if you're only applying to traditional biomedical PhD fields (immuno, neuro, molecular, biochem, etc.) then you shouldn't need anything beyond the MD requirements.