Methyldopa, an antihypertensive drug used mainly in the treatment of high blood pressure (especially in pregnancy), has a long history of clinical use and safety experience. It was developed in the early 1960s and became widely used because of its effectiveness in lowering blood pressure by acting centrally as an alpha-2 adrenergic agonist, which reduces sympathetic outflow from the brain. Methyldopa was one of the first well-established drugs considered safe for managing hypertension during pregnancy, making it an important option in obstetric care. Its development and approval led to widespread clinical adoption due to its predictable action and long-term safety data, although its use has declined in some settings with the availability of newer antihypertensive agents.
BRAND NAMES
Aldomet (most widely recognized brand)
Dopegyt
Aldoril
MECHANISM OF ACTION
Methyldopa is an antihypertensive drug that acts mainly as a centrally acting alpha-2 adrenergic agonist. After entering the body, it is converted in the brain to alpha-methylnorepinephrine, which stimulates alpha-2 receptors in the central nervous system.
PHARMACOKINETICS
Absorption
Methyldopa is incompletely absorbed from the gastrointestinal tract, with an oral bioavailability of about 25%. Absorption occurs mainly in the small intestine and may be reduced by food and certain antacids.
Distribution
Methyldopa has a moderate volume of distribution (Vd), approximately 0.6 L/kg, indicating that it is distributed into body tissues beyond the vascular compartment.
Metabolism
Methyldopa is partially metabolized in the liver to its active form, alpha-methylnorepinephrine, which is responsible for its antihypertensive effect. The drug undergoes hepatic metabolism mainly through decarboxylation and hydroxylation pathways.
Elimination
Methyldopa is primarily eliminated through the kidneys, with about 70–90% of the administered dose excreted in urine as unchanged drug and metabolites. A small portion is excreted in feces via biliary elimination.
PHARMACODYNAMICS
Methyldopa is a centrally acting antihypertensive agent that works as a prodrug. After entering the central nervous system, it is converted into alpha-methylnorepinephrine, which stimulates central alpha-2 adrenergic receptors in the brainstem. This activation reduces sympathetic nervous system outflow, leading to decreased release of norepinephrine from nerve endings. As a result, there is a reduction in peripheral vascular resistance, heart rate, and blood pressure.
ADMINISTRATION
Methyldopa is administered orally in tablet form for the treatment of hypertension. It is usually started at a low dose (e.g., 250 mg 2–3 times daily) and then gradually increased based on blood pressure response and patient tolerance. The usual maintenance dose ranges from 500 mg to 2 g per day, divided into 2–4 doses. In some cases, the total daily dose may be adjusted up to a maximum of about 3 g per day under medical supervision.
DOSAGE AND STRENGTH
Methyldopa is available in oral tablet form, commonly in strengths of 250 mg and 500 mg. The dosage is individualized based on the severity of hypertension and patient response. The usual starting dose is 250 mg two to three times daily, which may be gradually increased at intervals of at least 2 days.
DRUG INTERACTIONS
Use with tricyclic antidepressants or sympathomimetic drugs may reduce the antihypertensive effect of methyldopa. Iron supplements can decrease the absorption of methyldopa from the gastrointestinal tract, reducing its effectiveness, so dosing should be separated. Concomitant use with MAO inhibitors may lead to exaggerated hypotensive or central nervous system effects.
FOOD INTERACTIONS
Methyldopa has relatively few clinically significant food interactions, but food can slightly affect its absorption. Taking methyldopa with food may reduce gastrointestinal side effects such as nausea but can also slightly decrease its absorption, although this is usually not clinically important. Foods or supplements containing iron can significantly reduce the absorption of methyldopa by forming insoluble complexes in the gut, so iron supplements should be taken at least 2–4 hours apart from methyldopa.
CONTRAINDICATIONS
Methyldopa is contraindicated in patients with known hypersensitivity to the drug or any of its components. It should not be used in individuals with active liver disease, such as acute hepatitis or cirrhosis, because it can cause or worsen hepatotoxicity. It is also contraindicated in patients with previous methyldopa-induced liver dysfunction or hemolytic anemia.
SIDE EFFECTS
Drowsiness and sedation
Dry mouth
Headache
Dizziness or lightheadedness
Fatigue or weakness
Nasal congestion
OVER DOSE
Methyldopa overdose is characterized mainly by excessive central nervous system depression and severe hypotension due to exaggerated suppression of sympathetic activity. Symptoms may include marked drowsiness, dizziness, weakness, bradycardia, nausea, vomiting, and profound low blood pressure, which can lead to fainting or shock in severe cases.
TOXICITY
Methyldopa toxicity occurs mainly due to excessive accumulation or prolonged use and is characterized by enhanced pharmacological effects and immune-mediated reactions. The most important toxic effects include severe hypotension, excessive sedation, and central nervous system depression such as drowsiness, lethargy, and confusion. Hematologic toxicity may develop, including Coombs-positive hemolytic anemia, leukopenia, and thrombocytopenia due to immune-mediated mechanisms.
