Hunter × Hunter | Week 1 🐸

I wasn’t sure either so I checked another translation which said “Put this on your wound, to prevent gangrene”

So I think it’s using 塗(ぬ)る (to paint/plaster/smear) and 化(か)膿(のう)(festering).

jpdb parsed the grammar for ぬっとけ(塗っとけ)as the 〜とく form which is a contraction of 〜ておく (in advance/to prevent) so I reckon 〜とけ is the command form of that.