E.g. hydroxychloroquine variant developed outside institute by head of lab (9)
I believe the answer is:
antiviral
'head of lab' is the definition.
The definition suggests an adjective which matches the answer.
'e g hydroxychloroquine variant developed outside institute' is the wordplay.
I cannot quite understand how this works, but
'institute' could be 'i' (common abbreviation as in MIT) and 'i' is found within the answer.
an anagram of 'variant' is 'antvira' which is located in the remaining letters.
A single letter 'l' remains which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
'by' is the link.
(Other definitions for antiviral that I've seen before include "describing security software?" , "Like interferons" , "inhibiting disease" , "Drug" .)