Regular speedy cure worked out for libertine (7)
I believe the answer is:
seducer
'libertine' is the definition.
(seducer is a kind of libertine)
'regular speedy cure worked out' is the wordplay.
'regular' indicates alternate letters.
'worked out' indicates anagramming the letters.
The alternate letters of 'speedy' are 'sed'.
'cure' with letters rearranged gives 'ucer'.
'sed'+'ucer'='SEDUCER'
'for' acts as a link.
(Other definitions for seducer that I've seen before include "Rescued (anag) - Lothario" , "Wolf" , "One leading sexually astray" , "Casanova, for example" , "Rake" .)