But......Pamela wanted Steve dead immediately. John did think on his feet, saying there would be too many questions, better if it appears as if it was natural. THAT was to buy time. He got hold of Billie, and the antidote research was on. So, o.k. he administered the poison slowly, in small doses. When he decided he just could not continue, and smashed the vial, bingo, the guy following him appeared. Yep, he will kill Steve, his family, John, too & his family unless John goes thru.
Hey, I did not like it, most viewers did not. (if you cannot tell by my avatar, I am a huge Patch fan, lol)
O.K. he did not know there would be consequences, even with the antidote. But Kayla was deaf once upon a time, and regained her hearing, and as you noted, Salem water is fabulous. Heck, even those who have transplanted livers, hearts, etc. never even have to take anti-rejection meds. Bullet holes heal without scars, as do knife wounds, and all the other medical miracles that occur in Salem.