The letter D in 'MD' does not mean that the fix is DME-based!
The letter D signifies that the fix is part of an VOR/DME approach as I tried to mention earlier. It is an ARINC convention as noted by someone in this thread.
VORDME approach:
CD
FD
MD
VOR only approach:
CV
FV
MV
NDB only approach:
CQ
FQ
MQ
ILS approach:
CI
FI
MI
generic approach (where there is only 1 approach)
CF
FF
MF
There are a few more.
Also note that the database programmers do not always follow this convention.