Abbreviations

Q. What is the proper way to write Dr. Tom Smith Jr., M.D.?

A. Use MD or Dr., but not both. Please see CMOS 10.16 and 10.19. Some style guides use periods in M.D. and put a comma before Jr., but Chicago prefers the following forms:

Tom Smith Jr., MD
Dr. Tom Smith Jr.

[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]