|Trade names||Aldomet, Aldoril, Dopamet, others|
|Drug class||Alpha-2 adrenergic receptor agonist|
|Main uses||High blood pressure in pregnancy|
|by mouth, IV|
|Onset of action||4 to 6 hrs|
|Duration of action||10 to 48 hrs|
|Defined daily dose||1 to 2 gram|
|Elimination half-life||2 hours|
|Excretion||Kidney for metabolites|
|Chemical and physical data|
|Molar mass||211.217 g·mol−1|
|3D model (JSmol)|
Methyldopa, sold under the brand name Aldomet among others, is a medication used for high blood pressure. It is one of the preferred treatments for high blood pressure in pregnancy. For other types of high blood pressure including very high blood pressure resulting in symptoms other medications are typically preferred. It can be given by mouth or injection into a vein. Onset of effects is around 5 hours and they last about a day.
Common side effects include sleepiness. More severe side effects include red blood cell breakdown, liver problems, and allergic reactions. Methyldopa is in the alpha-2 adrenergic receptor agonist family of medication. It works by stimulating the brain to decrease the activity of the sympathetic nervous system.
Methyldopa was discovered in 1960. It is on the World Health Organization's List of Essential Medicines. The wholesale cost in the developing world is about US$4.31–9.48 per month. In the United States it costs less than $25 per month.
The defined daily dose is 1 gram for the levorotatory version and 2 grams for the racemic version. This is generally started at 250 mg two to three times a day for the first two days and than increased every few days by 250 mg until the typical long term dose of 1.5 grams is reached. The maximum dose is 3 grams.
Methyldopa is capable of inducing a number of adverse side effects, which range from mild to severe. Nevertheless, they are generally mild when the dose is less than 1 gram per day. Side effects may include:
- Depression or even suicidal ideation, as well as nightmares
- Apathy or anhedonia, as well as dysphoria
- Anxiety, especially of the social anxiety variant
- Decreased alertness, awareness, and wakefulness
- Impaired attention, focus, and concentration
- Decreased desire, drive, and motivation
- Fatigue or lethargy or malaise or lassitude
- Sedation or drowsiness or somnolence or sleepiness
- Agitation or restlessness
- Cognitive and memory impairment
- Derealization or depersonalization, as well as mild psychosis
- Sexual dysfunction including impaired libido, desire, and drive
- Dizziness, lightheadedness, or vertigo
- Miosis or pupil constriction
- Xerostomia or dry mouth
- Gastrointestinal disturbances such as diarrhea or constipation
- Headache or migraine
- Myalgia or muscle aches, arthralgia or joint pain, or paresthesia ("pins and needles")
- Restless legs syndrome (RLS)
- Parkinsonian symptoms such as muscle tremors, rigidity, hypokinesia, or balance or postural instability
- Akathisia, ataxia, dyskinesia as well as even tardive dyskinesia, or dystonia
- Bell's palsy or facial paralysis
- Sexual dysfunction consisting of impaired erectile dysfunction or anorgasmia
- Hyperprolactinemia or excess prolactin, gynecomastia/breast enlargement in males, or amenorrhoea or absence of menstrual cycles in females
- Bradycardia or decreased heart rate
- Hypotension or decreased blood pressure (though this may also be considered a therapeutic benefit)
- Orthostatic hypotension (also known as postural hypotension)
- Hepatitis, hepatotoxicity, or liver dysfunction or damage
- Pancreatitis or inflammation of the pancreas
- Warm autoimmune hemolytic anemia or deficiency in red blood cells (RBCs)
- Myelotoxicity or bone marrow suppression, potentially leading to thrombocytopenia or blood platelet deficiency or leukopenia or white blood cell (WBC) deficiency
- Hypersensitivity such as lupus erythematosus, myocarditis, or pericarditis
- Lichenoid reactions such as skin lesions or rashes
Mechanism of action
The mechanism of action of methyldopa is not fully clear. Although it is a centrally acting sympathomimetic, it does not block reuptake or transporters. It may reduce the dopaminergic and serotonergic transmission in the peripheral nervous system and it indirectly affects norepinephrine (noradrenaline) synthesis.
The S-enantiomer of methyldopa is a competitive inhibitor of the enzyme aromatic L-amino acid decarboxylase (LAAD), which converts L-DOPA into dopamine. L-DOPA can cross the blood brain barrier and thus methyldopa may have similar effects. LAAD converts it into alpha-methyldopamine, a false prescursor to norepinephrine, which in turn reduces synthesis of norepinephrine in the vesicles. Dopamine beta hydroxylase (DBH) converts alpha-methyldopamine into alpha-methylnorepinephrine, which is an agonist of the presynaptic α2-adrenergic receptor causing inhibition of neurotransmitter release.
When methyldopa was first introduced, it was the mainstay of antihypertensive treatment, but its use has declined on account of relatively severe adverse side effects, with increased use of other safer and more tolerable agents such as alpha blockers, beta blockers, and calcium channel blockers. Additionally, it has yet to be associated with reducing adverse cardiovascular events including myocardial infarction and stroke, or overall all-cause mortality reduction in clinical trials. Nonetheless, one of methyldopa's still current indications is in the management of pregnancy-induced hypertension (PIH), as it is relatively safe in pregnancy compared to many other antihypertensives which may affect the fetus.
- D-DOPA (dextrodopa)
- L-DOPA (levodopa; trade names Sinemet, Pharmacopa, Atamet, Stalevo, Madopar, Prolopa, etc.)
- L-DOPS (droxidopa)
- Dopamine (Intropan, Inovan, Revivan, Rivimine, Dopastat, Dynatra, etc.)
- Norepinephrine (noradrenaline; Levophed, etc.)
- Epinephrine (adrenaline; Adrenalin, EpiPed, Twinject, etc.)
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