Droxidopa

Droxidopa (INN; trade name Northera; also known as  L -DOPS,  L -threo-dihydroxyphenylserine, and SM-5688) is a synthetic amino acid precursor which acts as a prodrug to the neurotransmitters norepinephrine (noradrenaline) and epinephrine (adrenaline). Unlike norepinephrine and epinephrine themselves, droxidopa is capable of crossing the protective blood–brain barrier (BBB).

Indications

 * Neurogenic orthostatic hypotension (NOH), as well as NOH associated with multiple system atrophy (MSA), familial amyloid polyneuropathy (FAP), pure autonomic failure (PAF), and Parkinson's disease (PD).
 * Intradialytic hypotension (IDH) or hemodialysis-induced hypotension.
 * Hypotension associated with fibromyalgia syndrome (FMS) and chronic fatigue syndrome (CFS).

History
Droxidopa was developed by Sumitomo Pharmaceuticals for the treatment of hypotension, including NOH, and NOH associated with various disorders such as MSA, FAP, and PD, as well as IDH. The drug has been used in Japan and some surrounding Asian areas for these indications since 1989. Following a merge with Dainippon Pharmaceuticals in 2006, Dainippon Sumitomo Pharma licensed droxidopa to Chelsea Therapeutics to develop and market it worldwide except in Japan, Korea, China, and Taiwan. In February 2014, the Food and Drug Administration approved droxidopa for the treatment of symptomatic neurogenic orthostatic hypotension.

Clinical trials
To support additional indications beyond its approval in the US for NOH, phase II clinical trials for IDH are also underway. Chelsea Therapeutics obtained orphan drug status (ODS) for droxidopa in the U.S. for NOH, and that of which associated with PD, PAF, and MSA, and is the pharmaceutical company developing it in that country.

Pharmacology
Droxidopa is a prodrug of norepinephrine and epinephrine used to increase the concentrations of these neurotransmitters in the body and brain. It is metabolized by aromatic L-amino acid decarboxylase (AAAD), also known as DOPA decarboxylase (DDC). Patients with NOH have depleted levels of norepinephrine and epinephrine which leads to decreased blood pressure or hypotension upon orthostatic challenge. Droxidopa works by increasing the levels of norepinephrine and epinephrine in the peripheral nervous system (PNS), which induces tachycardia or increased heart rate and hypertension or increased blood pressure, thus enabling the body to maintain blood flow upon and while standing.

Droxidopa can also cross the blood–brain barrier (BBB) where it is converted to norepinephrine and epinephrine from within the brain. Increased levels of norepinephrine and epinephrine in the central nervous system (CNS) may be beneficial to patients in a wide range of indications. Droxidopa can be coupled with a peripheral aromatic L-amino acid decarboxylase inhibitor (AAADI) or DOPA decarboxylase inhibitor (DDC) such as carbidopa (Lodosyn) to increase central norepinephrine and epinephrine concentrations while maintaining peripheral levels.

Side effects
With close to 20 years on the market, droxidopa has proven to have very few side effects of which most are mild. Patients have reported tachycardia, hypertension, nausea and vomiting, and headache or migraine.