AT: "xx" Trioxin was a medicine used in the treatment of respiratory injuries. It was used in emergency situations as a stop-gap measure; doctors usually preferred to treat the injury itself if they had the time and capability.
During the assent of the Nezu orbital tether in 2373, Tuvok used trioxin to ease the effects of hypoxia on the cart's crew. (VOY: "Rise")
In an alternate timeline, The Doctor was ordered by Captain Janeway to inject her with trioxin after her alveoli were damaged by nebular gas in 2374. (VOY: "Year of Hell, Part II")