Honestly, Michizane didn't even have much to play with. Realistically speaking, Yoshio would probably already be dead by the time Michizane arrived there (you probably don't have a lot of time left if you start VOMITING BLOOD). So, I'm giving him a passing grade just for trying at all. Eliminating whatever poison hasn't been absorbed yet is good enough if you don't even know what he drank exactly. Maybe giving a diuretic too would've been ideal (like ginger tea I guess?)
(Btw I know how I made it sound, but I'm only on my third year of university. I'm by no means an expert.)
Such a shame they didn't have phones back then though. He should've put Maomao on the line to help him (now I'm getting ideas for a crossover).