Calling nurse to inject drug (6)
I believe the answer is:
career
'calling' is the definition.
('career' can be a synonym of 'calling')
'nurse to inject drug' is the wordplay.
'nurse' becomes 'carer' (I've seen this before).
'to inject' is an insertion indicator.
'drug' becomes 'e' (e is another name for ecstasy).
'carer' going around 'e' is 'CAREER'.
(Other definitions for career that I've seen before include "Long-time occupation" , "Rush headlong" , "race" , "someone in profession" , "Business course through life" .)