I name patient, as a precaution (2,4)
I believe the answer is:
in case
'as a precaution' is the definition.
(I've seen this before)
'i name patient' is the wordplay.
'name' becomes 'n' (common abbreviation e.g. on forms).
'patient' becomes 'case' ('case' can be a synonym of 'patient').
'i'+'n'+'case'='IN CASE'
(Other definitions for in case that I've seen before include "Packed" , "for emergency" , "Where traveller may keep clothes" , "In order to allow for eventualities" , "As a precaution" .)