Dose Response to the Norepinephrine Precursor Droxidopa in Hypotensive Individuals With Spinal Cord Injury

Interruption of sympathetic cardiovascular autonomic regulation following spinal cord injury (SCI) is associated with significantly reduced plasma norepinephrine (NE) levels, hypotension and orthostatic hypotension (OH), particularly in individuals with high cord lesions. Although the incidence of hypotension is reported to be as high as 70% in persons with cervical lesions (i.e., tetraplegia), the vast majority of these individuals remains asymptomatic and, therefore, does not raise clinical concern, or prompt intervention. While it is appreciated that clinicians are faced with substantial challenges in managing blood pressure (BP) in persons with SCI, contrary to the prevailing belief, asymptomatic hypotension and OH are not benign conditions. Reports suggest that asymptomatic hypotensive individuals with SCI may have subclinical cognitive dysfunction affecting memory and attention processing and increased incidence of fatigue and depression compared to normotensive individuals with SCI. It must be appreciated that to date, there are no FDA approved pharmaceutical options proven to be safe and effective for treatment of hypotension and OH in the SCI population. Until 2014, midodrine hydrochloride was the only agent with FDA approval for treatment of symptomatic neurogenic OH (NOH). Midodrine, an alpha-agonist, is the most commonly prescribed agent used to treat symptomatic hypotension in the SCI population despite a lack of convincing evidence of safety or efficacy. In 2014 droxidopa (L-threo-3,4-dihydroxyphenylserine - NORTHERA; Chelsea Therapeutics, Charlotte, NC) was approved by the FDA for treatment of symptomatic NOH based on data collected in conditions of autonomic dysfunction. Droxidopa is a NE precursor that is stored in neuronal and non-neuronal tissue and has been shown to increase standing BP and reduce symptoms of orthostatic intolerance in individuals with symptomatic NOH. We recently reported preliminary evidence of a mean increase in seated BP in individuals with SCI following oral administration of 400 mg of droxidopa; however, this dose was effective in only 5 of the 10 subjects tested and the BP effect waned over a 4-hour observation. Because of its unique pharmacokinetic profile, droxidopa is a highly promising agent to treat hypotension in persons with SCI. As such; there exists a pressing imperative to determine the clinical value and safety of droxidopa in hypotensive individuals with SCI.

Inclusion criteria

Study 1:

• Male or Female, age 18 to 89 with traumatic SCI.
• SCI Subjects (n=40):

• Any level of injury;
• Any American Spinal Injury Association Impairment Scale (AIS) grade of SCI;
• Non-ventilator dependent
• Primarily wheelchair dependent for mobility;
• Duration of injury < 1 year
• Low Blood Pressure:

• Systolic BP less than 110 mmHg and/or diastolic BP less than 70 mmHg for males.
• Systolic BP less than 100 mmHg and/or diastolic BP less than 70 mmHg for females.
• Primary Language is English.
• Able to provide informed consent

Study 2:

• Male or Female, age 18 to 89 with traumatic SCI.
• SCI Subjects (n=40):

• Any level of injury;
• Any AIS grade of SCI;
• Non-ventilator dependent
• Primarily wheelchair dependent for mobility
• Duration of injury < 1 year
• Low Blood Pressure:

• Systolic BP less than 110 mmHg and/or diastolic BP less than 70 mmHg for males.
• Systolic BP less than 100 mmHg and/or diastolic BP less than 70 mmHg for females.
• Primary Language is English.
• Able to provide informed consent
• Showed a normotensive blood pressure in response to Droxidopa during study 1.

Exclusion criteria

• Current illness or infection
• Individuals with frequent or severe autonomic dysreflexia:

• More than 3 symptomatic events per week
• BP ≥140/90 mmHg
• Significant adverse subjective symptoms reporting
• Hypertension
• Any neurological condition other than SCI (Alzheimer's disease, dementia, stroke, multiple sclerosis, Parkinson's disease, etc.)
• History of epilepsy or other seizure disorder
• History of traumatic brain injury (TBI)
• Liver or kidney disease
• Bladder problems including blockage of the urine and/or weak urine stream.
• Diagnosis of a psychiatric disorder such as schizophrenia or bipolar disorder
• Known artery disease, heart failure, Atrio-ventricular block, and irregular heartbeat
• Any allergies to droxidopa, asprin, polyethylene oxide, polyethylene glycol, hydroxypropyl cellulose, butylated hydroxytoluene, magnesium stearate, hypromellose, yellow ferric oxide, and red ferric oxide
• Major surgery in the last 30 days
• Illicit drug abuse in the past 6 months
• Pregnant
• Your prescription medications will be reviewed by the study investigators and research staff. If you are currently taking medications to treat any of the following please make the investigators aware:

d. Depression, Schizophrenia, Attention Deficit Hyperactivity Disorder (ADHD) e. Pain (opioids) f. Infection or illness (antibiotics) g. Erectile dysfunction (Viagra, Cialis, etc.) h. Overactive bladder i. High or low blood pressure j. Migraine headaches k. Malaria l. asthma