After administration of single 100 mg and 300 mg doses to healthy volunteers, droxidopa, 3-OM-DOPS, and NE were observed in the urine. The 24-hour excretions of droxidopa and 3-OM-DOPS accounted for approximately 15% and 8% of the administered dose (3-OM-DOPS uncorrected for molecular weight), suggesting that renal function may impact the clearance of droxidopa and 3-OM-DOPS.1,2 A population PK study conducted in patients with Primary Autonomic Failure indicated that increasing age was associated with decreased clearance of both droxidopa and 3 OM DOPS (Apparent clearance decreased 0.8% per year of age [referenced to age 65 years]). Further it was identified that patient's concurrently taking L-Dopa or dopamine derivatives had approximately 50% of the clearance seen with patients not taking droxidopa. 6 From a safety perspective, droxidopa has been generally very well-tolerated across a large variety of patient populations.