A resuscitative medicine carried in every Starfleet sickbay of the 24th century, given by hypospray to stabilise the heart and nervous system of critically injured or collapsing patients.
Inaprovaline is one of the standard emergency drugs of 24th-century Federation medicine. It is given by hypospray to patients whose heart or neural activity is failing, and it is usually the first thing a Starfleet doctor calls for when someone is brought into sickbay close to death.
Beverly Crusher uses it on the gravely injured Zalkonian the crew call John Doe in the Next Generation episode Transfigurations, and it is tried without success when Worf's life signs fail on the operating table in Ethics. Julian Bashir and Voyager's Doctor order it just as routinely in Deep Space Nine and Voyager.
The drug is never explained in detail on screen; it simply fills the role that cordrazine played in the 23rd century, and its name became a familiar piece of the franchise's medical vocabulary.