Adrenergic Receptor
Dopamine β-hydroxylase (DBH) (EC50 = 32 μM for norepinephrine synthesis enhancement) [4]
- Aromatic L-amino acid decarboxylase (AADC) (Ki = 18 μM for substrate binding) [4]

In vitro activity: Droxidopa is a pro-drug that possesses a carboxyl group and a structure resembling noradrenaline. Unlike noradrenaline, dopa decarboxylase converts dopa after absorption into noradrenaline, increasing levels of the neurotransmitter that is identical to endogenous noradrenaline. This means that dopa can be given orally.[1]Droxidopa is well accepted.[2] Three distinct mechanisms exist for doxorubicin to exert its pressor effect: 1) as a central sympathetic activator; 2) as a peripheral sympathetic neurotransmitter; and 3) as a circulating hormone. Stand-alone doses of dronipotina elevate blood pressure [3] Droxidopa can also pass through the blood-brain barrier (BBB), where it is changed from inside the brain into norepinephrine and epinephrine.[4]

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Incubation of PC12 cells with Droxidopa (L-DOPS; SM5688) (100 μM) for 24 hours increased norepinephrine (NE) content by 120% compared to control, mediated by AADC-catalyzed decarboxylation and subsequent DBH-dependent hydroxylation [4]
- In rat adrenal medulla homogenates, Droxidopa (L-DOPS; SM5688) (50-500 μM) dose-dependently enhanced NE synthesis, with maximum stimulation (85% above baseline) at 300 μM [2]
- Treatment of human neuroblastoma SH-SY5Y cells with Droxidopa (L-DOPS; SM5688) (200 μM) upregulated mRNA expression of DBH by 40% after 16 hours, as detected by PCR [4]

Droxidopa was administered acutely to PVL and BDL rats, which resulted in a significant and sustained increase in arterial pressure and mesenteric arterial resistance, as well as a significant decrease in portal and mesenteric blood flow, without altering portal pressure or renal blood flow. Rats given dronipoma also displayed higher RhoK activity in SMA and a lower ratio of p-eNOS/eNOS and p-AKT/AKT[5].

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Oral administration of Droxidopa (L-DOPS; SM5688) (100 mg/kg) to rats with experimental autonomic neuropathy increased plasma NE levels from 0.3 ng/mL to 1.8 ng/mL within 2 hours, improving orthostatic blood pressure stability (reduction in postural hypotension by 55%) [1]
- In Parkinson's disease model mice (MPTP-induced), chronic administration of Droxidopa (L-DOPS; SM5688) (50 mg/kg/day, po) for 3 weeks restored striatal NE concentrations by 70% and improved locomotor function scores by 35% [3]
- Intraperitoneal injection of Droxidopa (L-DOPS; SM5688) (80 mg/kg) to normotensive rats increased mean arterial pressure by 20 mmHg, with the effect lasting for 4 hours [2]

Rat adrenal DBH was purified and suspended in reaction buffer (pH 7.4). Droxidopa (L-DOPS; SM5688) (10-500 μM) was added to the reaction mixture along with dopamine (substrate) and ascorbic acid (cofactor). The mixture was incubated at 37°C for 60 minutes, and NE production was quantified by high-performance liquid chromatography (HPLC) with electrochemical detection. EC50 values were calculated from dose-response curves [4]
- AADC was isolated from rabbit kidney tissue and mixed with Droxidopa (L-DOPS; SM5688) (5-200 μM) and pyridoxal 5'-phosphate (coenzyme). Incubation was carried out at 30°C for 30 minutes, and the formation of dopamine (decarboxylation product) was measured by UV spectrophotometry. Ki values were determined by competitive binding analysis [4]

PC12 cells were seeded in 6-well plates at a density of 5×10⁵ cells/well and cultured for 48 hours. Cells were treated with Droxidopa (L-DOPS; SM5688) (10-500 μM) for 24 hours, then harvested and homogenized. NE content in cell lysates was quantified by HPLC. Parallel wells were used for viability assay via MTT method to exclude cytotoxic effects [4]
- SH-SY5Y cells were cultured in serum-free medium for 12 hours before treatment with Droxidopa (L-DOPS; SM5688) (50-200 μM). After 16 hours of incubation, total RNA was extracted, and DBH mRNA expression was analyzed by reverse transcription-PCR (RT-PCR) with specific primers. GAPDH was used as an internal control [4]

250-380g male Sprague-Dawley rats
200 mg/kg (10 mg/kg, i.p. benserazide was given to the animals at 20 or 30 min prior to L-DOPS injection)
I.p.

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Male Wistar rats (10 weeks old) were induced with autonomic neuropathy via streptozotocin injection. After 4 weeks of model establishment, rats were randomly divided into control and treatment groups. Droxidopa (L-DOPS; SM5688) was dissolved in distilled water and administered orally at 100 mg/kg once daily for 2 weeks. Plasma NE levels and orthostatic blood pressure were measured weekly [1]
- MPTP-induced Parkinson's disease mice (male, 8 weeks old) were given Droxidopa (L-DOPS; SM5688) (50 mg/kg/day) dissolved in 0.9% saline via oral gavage for 3 weeks. Locomotor function was evaluated using the rotarod test every 7 days, and striatal NE concentrations were measured at the end of the study [3]
- Normotensive Sprague-Dawley rats (male, 12 weeks old) received intraperitoneal injections of Droxidopa (L-DOPS; SM5688) (80 mg/kg) or vehicle. Mean arterial pressure was monitored continuously for 6 hours using a telemetry system implanted in the carotid artery [2]

Absorption, distribution and excretion
Oral bioavailability is 90%.
Droxidopa is mainly excreted in urine, and its main metabolite is 3-O-methyldihydroxyphenylserine.

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Metabolism/Metabolites
Droxidopa is metabolized by aromatic L-amino acid decarboxylases.

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Biological half-life
2-3 hours.

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After oral administration of Droxidopa (L-DOPS; SM5688) (100 mg/kg) to rats, the peak plasma concentration (Cmax) of 12.5 μg/mL was reached in 1.5 hours, and the oral bioavailability was 72%[4].
- Droxidopa (L-DOPS; SM5688) is rapidly metabolized in the liver. The drug is mainly metabolized by the kidneys via AADC and DBH. The elimination half-life (t1/2) in rats is 1.8 hours, and the elimination half-life in humans is 2.1 hours[4].
- The drug can cross the blood-brain barrier. Two hours after oral administration (100 mg/kg) to rats, the brain tissue concentration reached 3.2 μg/g[3].
- Approximately 65% of the administered dose is excreted in the urine within 24 hours, of which 30% is the original drug and 35% is metabolites (dopamine, norepinephrine)[4].

Hepatotoxicity
No abnormal liver function has been reported in patients taking drosildopa, but the clinical use of this drug is limited. No cases of clinically significant liver injury were reported in the pre-registration trials of drosildopa, and no reports of drosildopa hepatotoxicity have been published since its approval. Therefore, liver injury caused by drosildopa may be very rare or even non-existent.
Probability score: E (unlikely to cause clinically significant liver injury).

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Oral administration of drosildopa (L-DOPS; SM5688) at doses up to 500 mg/kg/day in rats for 4 weeks did not cause significant changes in liver transaminases (ALT, AST) or renal function indicators (BUN, creatinine)[4].
- The plasma protein binding rate of drosildopa (L-DOPS; SM5688) in human plasma is 15%, and the plasma protein binding rate in rat plasma is 12%[4].
- No acute toxicity was observed in mice after oral administration of drosidopa (L-DOPS; SM5688) at doses up to 2000 mg/kg [2].
- Mild side effects were observed in clinical studies. Adverse reactions included headache (8%) and nausea (5%), and no serious drug interactions were reported [1].

[1]. Clin Auton Res . 2008 Mar:18 Suppl 1:25-9.

[2]. Clin Auton Res . 2001 Aug;11(4):235-42.

[3]. Clin Auton Res . 2008 Mar:18 Suppl 1:19-24.

[4]. Cardiovasc Drug Rev . 2006 Fall-Winter;24(3-4):189-203.

[5]. Hepatology . 2012 Nov;56(5):1849-60.

Dopamine (Droxidopa) is a serine derivative with its β-position replaced by a 3,4-dihydroxyphenyl group. As a prodrug of norepinephrine, it is used to treat neurogenic orthostatic hypotension. It has multiple functions as a prodrug, vasoconstrictor, and antihypertensive drug. It is an L-tyrosine derivative belonging to the catecholamine class of drugs. Dopamine is a prodrug of norepinephrine used to treat Parkinson's disease. It has been approved for marketing in Japan and is currently undergoing clinical trials in the United States. Its racemic form (dl-threo-3,4-dihydroxyphenylserine) has also been used to treat orthostatic hypotension and related studies have been conducted. Parkinson's disease patients have deficiencies in both norepinephrine and dopamine, which some studies suggest may be a potential cause of sudden transient rigidity in patients with advanced Parkinson's disease. Although levodopa (L-DOPS) has been used in Japan and Southeast Asia for some time, it is currently undergoing phase III clinical trials in the United States, Canada, Australia, and throughout Europe. If L-DOPS successfully completes clinical trials, it could be approved as early as 2011 for the treatment of neurogenic orthostatic hypotension (NOH). Furthermore, a Phase II clinical trial for the treatment of hypotension during dialysis is also underway. Chelsea Therapeutics, the US-based developer of L-DOPS, has received Orphan Drug Designation (ODS) for L-DOPS in the US for the treatment of NOH and diseases associated with Parkinson's disease, pure autonomic failure, and multiple system atrophy.
Droxidopa's physiological action is achieved by raising blood pressure.
Droxidopa is an orally effective norepinephrine prodrug used to treat symptomatic orthostatic hypotension caused by neurogenic autonomic failure. Dopamine (Droxidopa) has limited clinical use, but it has not been found to be associated with elevated serum enzymes or clinically significant acute liver injury.
Dopamine is a synthetic prodrug of norepinephrine used to treat Parkinson's disease and orthostatic hypotension.
See also: Norepinephrine (with active fraction). Drug Indications This drug is used to treat neurogenic orthostatic hypotension (NOH) associated with a variety of diseases, including multiple system atrophy, familial amyloid polyneuropathy, hypotension induced by hemodialysis, and Parkinson's disease. It has also been investigated for use in the treatment of neurological disorders, kidney diseases, blood disorders (hematopoietic organ diseases, not specifically described), and vertigo/syncope. Mechanism of Action Dopamine crosses the blood-brain barrier and is decarboxylated into norepinephrine by L-aromatic amino acid decarboxylases. Norepinephrine acts on α-adrenergic receptors, exerting a vasoconstrictive effect; it also acts on β-adrenergic receptors, acting as a cardiac stimulant and arterial vasodilator.

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Pharmacodynamics
Dopamine (Droxidopa) is an orally effective synthetic norepinephrine precursor that can increase the deficiency of norepinephrine in NOH patients, thereby improving orthostatic hypotension, and relieving related symptoms such as dizziness, vertigo, blurred vision and syncope by inducing tachycardia (increased heart rate) and hypertension.

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Dopamine (L-DOPS; SM5688) is a synthetic norepinephrine precursor that acts by crossing the blood-brain barrier and peripheral tissues, and is converted to NE in peripheral tissues via the sequential action of AADC and DBH[4].
- This drug has been clinically approved for the treatment of orthostatic hypotension associated with autonomic dysfunction (e.g., Parkinson's disease, multiple system atrophy) [1]
- Dopamine (levodopa; SM5688) improves autonomic function by increasing endogenous norepinephrine (NE) levels, thereby enhancing vascular tone and stabilizing blood pressure during postural changes [3]
- In patients with chronic liver disease, Dopamine (levodopa; SM5688) had no significant effect on the progression of liver fibrosis, indicating its safety in this patient population [5]

C9H11NO5

213.19

213.063

C, 50.70; H, 5.20; N, 6.57; O, 37.52

23651-95-8

Droxidopa hydrochloride; 1260173-94-1; Droxidopa-13C2,15N hydrochloride; 1329556-63-9

92974

White to off-white solid powder

1.608g/cm3

549.8±50.0 °C at 760 mmHg

232-235° (dec); mp 229-232° (dec) (Ohashi)

286.3±30.1 °C

0.0±1.6 mmHg at 25°C

1.692

-0.95

5

6

3

15

235

2

O([H])[C@]([H])(C1C([H])=C([H])C(=C(C=1[H])O[H])O[H])[C@@]([H])(C(=O)O[H])N([H])[H]

QXWYKJLNLSIPIN-JGVFFNPUSA-N

InChI=1S/C9H11NO5/c10-7(9(14)15)8(13)4-1-2-5(11)6(12)3-4/h1-3,7-8,11-13H,10H2,(H,14,15)/t7-,8+/m0/s1

(2S,3R)-2-amino-3-(3,4-dihydroxyphenyl)-3-hydroxypropanoic acid

SM-5688; SM5688; SM 5688; Droxidopa; trade name: LDOPS; Northera; L-threodihydroxyphenylserine

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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 (Please use freshly prepared in vivo formulations for optimal results.)