Sustained Effect of Droxidopa in Symptomatic Neurogenic Orthostatic Hypotension

Inclusion Criteria: * 18 years or older and able to stand (with or without limited assistance) * Clinical diagnosis of symptomatic orthostatic hypotension associated with Primary Autonomic Failure (PD, MSA or PAF) or NDAN or DBH Deficiency * Score of at least 4 or greater on Orthostatic Hypotension Symptom Assessment (OHSA) Item #1 (measured at Screening \[Visit 1\] and the first Titration Visit \[Visit 2a\] prior to dosing) * A documented drop of at least 20 millimeters of mercury (mmHg) in SBP, within 3 minutes of standing. This can either be documented in the patient history or assessed during Screening prior to the first Titration Visit (Visit 2a) * Provide written informed consent to participate in the study and understand that they may withdraw their consent at any time without prejudice to their future medical care Additional inclusion criteria for patients taking prescribed droxidopa prior to study entry: Patients who are taking prescribed droxidopa therapy are eligible to participate in the study if they meet the other inclusion criteria and also have been on a stable dose of prescribed droxidopa for at least 2 weeks prior to the Screening Visit (Visit 1). In addition, they must meet either of the following at the Screening Visit (Visit 1): * The patient's Visit 1 OHSA Item #1 score is ≥ 7 AND the prescribed dose is ≤ 300 mg three times daily (TID); OR * The patient's Visit 1 OHSA Item #1 score is ≤6 AND worsens by ≥ 2 units when retested after washing out of dro…