Turning endlessly to nurse: medicine's first remedy (7)
I believe the answer is:
nostrum
'remedy' is the definition.
(I know that nostrum is a type of remedy)
'turning endlessly to nurse medicine's first' is the wordplay.
'turning' indicates anagramming the letters.
'endlessly' means to remove the last letter.
'medicine's first' becomes 'm' (1st letter of 'medicine').
'to'+'nurse'='tonurse'
'tonurse' with its final letter taken off is 'tonurs'.
'tonurs' anagrammed gives 'nostru'.
'nostru'+'m'='NOSTRUM'
(Other definitions for nostrum that I've seen before include "Quack cure" , "Phoney panacea" , "Must Ron take a quack remedy?" , "Some think it helps" , "Panacea or cure-all" .)