I dose child with rum mixture containing zero salt (6,8)
I believe the answer is:
sodium chloride
'salt' is the definition.
(sodium chloride is a kind of salt)
'i dose child with rum mixture containing zero' is the wordplay.
'with' is a charade indicator (letters next to each other).
'mixture' indicates an anagram.
'containing' is an insertion indicator.
'zero' becomes 'O' (O resembles 0).
'i'+'dose'+'child'+'rum'='idosechildrum'
'idosechildrum' is an anagram of 'sodiumchlride'.
'sodiumchlride' enclosing 'o' is 'SODIUM CHLORIDE'.
(Another definition for sodium chloride that I've seen is " It's found in the ocean".)