Patient is treated with cold disinfectant (10)
I believe the answer is:
antiseptic
'disinfectant' is the definition.
('antiseptic' can be similar in meaning to 'disinfectant')
'patient is treated with cold' is the wordplay.
'treated with' is an anagram indicator.
'cold' becomes 'c' (eg on taps).
'patient'+'is'='patientis'
'patientis' anagrammed with 'c' makes 'ANTISEPTIC'.
(Other definitions for antiseptic that I've seen before include "Clinical" , "treatment" , "Preventing growth of microorganisms" , "Designed to counteract infection" , "Preventing growth of, eg, bacteria" .)