Benzethonium chloride (C27H47ClNO2) was a painkiller used in hospitals.
In 2151, following a rock climbing accident on Risa, Ensign Travis Mayweather was given benzethonium chloride at a Risan hospital. He turned out to be highly allergic to it, and suffered from swelling that threatened to constrict his airway. (ENT: "Two Days and Two Nights")