A total of 48 male or female subjects, 16 subjects with normal renal function (eGFR greater than 90 mL/min/1.73m²) and eight each (8) with mild (60 less than eGFR less than 89 mL/min/1.73m²), moderate (30 less than eGFR less than 59 mL/min/1.73m²), or severe (15 less than eGFR less than 29 mL/min/1.73m²) renal impairment or ESRD (eGFR < 15 mL/min/1.73m² and requiring hemodialysis) will be selected according to the inclusion and exclusion criteria. The medical and laboratory examinations will take place within 28 days before dosing. A single dose of 600 mg of droxidopa as an investigational drug will be administered with 240 mL of water after an overnight fast (minimum 10 hours).