Not keen on new rival type of drug (9)
I believe the answer is:
antiviral
'type of drug' is the definition.
(antiviral is a type of drug)
'not keen on new rival' is the wordplay.
'not keen on' becomes 'anti' (anti means hostile or opposed to).
'new' is an anagram indicator.
'rival' anagrammed gives 'viral'.
'anti'+'viral'='ANTIVIRAL'
(Other definitions for antiviral that I've seen before include "inhibiting disease" , "Like interferons" , "Drug" , "describing security software?" .)