Throw in Candide every so often (3)
I believe the answer is:
add
'throw in' is the definition.
(I've seen this in another clue)
'candide every so often' is the wordplay.
'every so often' indicates alternate letters.
The alternate letters of 'candide' are 'ADD'.
(Other definitions for add that I've seen before include "Count up" , "Include" , "Total; put together" , "Give more" , "Contribute" .)