Hextech gunblade on fizz

Have seen a few players absolutely dominating and solo carrying games on hextech fizz, each time they have been very good fizz players and usually snowballed out of control, but when my adc gets 1 shot by a fizz q under fountain i gotta ask, what do i do against that, he eats locket with his passive burn and his burst + health gain [spellvamp] from hextech is unreal.