Medic works on last bit of nasty complaint (6)
I believe the answer is:
dropsy
'complaint' is the definition.
(medical complaint)
'medic works on last bit of nasty' is the wordplay.
'medic' becomes 'dr' (doctor).
'works' becomes 'ops' (op is short for opus, a work).
'on' says to put letters next to each other.
'last bit of' suggests the final letters.
The last letter of 'nasty' is 'y'.
'dr'+'ops'+'y'='DROPSY'
(Other definitions for dropsy that I've seen before include "Oedema (old name)" , "Accumulation of fluid in a part of the body - oedema" , "fluid build-up" , "illness" , "medical condition" .)