This card has three NPCs connected to it — the physician who commissioned the needle, the unnamed smith who made the needle, and the guild representative the physician (potentially) intended to kill with the needle. Using the weapon to put the NPCs on your players' radar is a great way to kick off a larger quest, and doing the inverse is a great way to offer smaller ones. The focus on rumors and controversy (instead of concrete antagonism between Cuthold and Erneiros) makes it easy to adapt the motives of NPCs involved to fit the story you want to tell, too.
Maybe the needle really was meant for tranquilizing rhinoceroses. Maybe Cuthold was gearing up to assassinate someone completely unrelated to Erneiros. Maybe Cuthold intercepted the weapon to keep the real commissioner from using it, deliberately stoking the controversy surrounding it in order to give himself an exit from a suddenly-dangerous court. Who knows? Maybe Erneiros does. Or the smith. Or the courier who delivered the needle. That's up to you.
On the mechanics front, I want to stress that just because the needle *can* hold an utterly terrifying amount of poison doesn't mean you should give it to your players *pre-loaded* with an utterly terrifying amount of poison. Make them put some work in, and don't be afraid to use that 'must be diluted' line to keep them from pumping a forgotten big gulp of nasty juice from eight sessions ago directly into your BBEG.
Similarly, don't discount the fact that there's a Misfire 1 property on there. It doesn't have a huge impact on the average damage output in a vacuum, but it comes up just enough in real play to keep things interesting and it gives you a way (repair DCs) to tune the damage output.
May 18th: Template Update