In vitro activity: Droxidopa is a pro-drug which has a structure similar to noradrenaline, but with a carboxyl group. Droxidopa can be administered orally, unlike noradrenaline, and after absorption is converted by the enzyme dopa decarboxylase into noradrenaline thus increasing levels of the neurotransmitter which is identical to endogenous noradrenaline. Droxidopa is well tolerated. Droxidopa could exert its pressor effect in three different ways: a) as a central stimulator of sympathetic activity; b) as a peripheral sympathetic neurotransmitter; c) as a circulating hormone. Droxidopa taken alone increases standing blood pressure. Droxidopa can also cross the blood–brain barrier (BBB) where it is converted to norepinephrine and epinephrine from within the brain.

Clin Auton Res. 2008 Mar;18 Suppl 1:25-9; Clin Auton Res. 2001 Aug;11(4):235-42.