Lastly, shake anti-viral fluid before opening it (7,8)
I believe the answer is:
italian vermouth
'it' is the definition.
(I've seen this before)
'lastly shake anti-viral fluid before opening' is the wordplay.
I cannot really see how this works, but
'fluid' could be 'vermouth' (vermouth is a kind of fluid) and 'vermouth' is found within the answer.
The remaining letters 'italian' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for italian vermouth that I've seen before include "Drink" , "two words for it!" , "It expanded" .)