Iodine for one upset (not terminally sick) patient (10)
I believe the answer is:
'iodine for one' is the definition.
(iodine is a kind of antiseptic)
'upset not terminally sick patient' is the wordplay.
'upset' is an anagram indicator.
'not terminally' means to remove the last letter.
'sick' with its final letter taken off is 'sic'.
'sicpatient' is an anagram of 'ANTISEPTIC'.
(Other definitions for antiseptic that I've seen before include "Clinical" , "germicide" , "Designed to counteract infection" , "Preventing growth of, eg, bacteria" , "treatment" .)