I remember he applied an antidote (I assume, it just jumped from "I should probably use an antidote on this" to him wrapping up his hand post-fight), but I wonder if he thought to maybe check if a gigantic snake required something specific.
Unless there was just nowhere to stop that would have something like that between the forest and where they had to teleport to. Just seems like a bit of an oversight from an apothecary, if there was something he could have done about it before that point.
Hopefully the gigantic Yeti coming to check out the distress signal knows a thing or two about snake venom, being up in snow-capped mountains and all.