Note from me to doctor (4)
I believe the answer is:
memo
'note' is the definition.
(memo is a kind of note)
'me to doctor' is the wordplay.
'to doctor' becomes 'mo' (medical officer**).
'me'+'mo'='MEMO'
'from' is the link.
(Other definitions for memo that I've seen before include "Reminder (abbr)" , "diplomatic communication?" , "Inter-office note" , "- Currie, Br. politician" , "Businesslike message" .)