The investigators propose to perform a double-blind randomized trial with a cross over design to compare high dose (600 mg/day) and low dose (300 mg per day) carbidopa blockade with placebo. Patients will be randomly assigned to a high-dose/low-dose/placebo sequence, lowdose/placebo/high-dose sequence or placebo/high-dose/low-dose sequence. Participants will remain on each treatment period for 28-days.
Aim 1: To evaluate the safety and tolerability of carbidopa in FD patients with particular emphasis on the orthostatic fall in blood pressure.
Aim 2: As proof of concept, examine the hemodynamic effects of carbidopa and determine its effects on norepinephrine production, BP variability and paroxysmal hypertension.
Aim 3: In a dose finding study, compare the effects of low (300 mg/day) and high (600 mg/day) dose carbidopa blockade vs. placebo on BP variability and paroxysmal hypertension.
