Medics going to S American capital city fly (8)
I believe the answer is:
mosquito
'fly' is the definition.
(I've seen this before)
'medics going to s american capital city' is the wordplay.
'medics' becomes 'mos' (I've seen this in other clues).
'going to' is a charade indicator (letters next to each other).
's american capital city' becomes 'Quito' (capital of Ecuador).
'mos'+'quito'='MOSQUITO'
(Other definitions for mosquito that I've seen before include "Sucker" , "Insect, the female of which sucks blood" , "WW2 fighter plane" , "Annoying insect" , "Plane used in WWII" .)