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CAS Number


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Product Name:
CAS Number:
For use in the treatment of hypertension.
Mode of Action:

Although the mechanism of action has yet to be conclusively demonstrated, the resultant hypotensive effect is most likely due to the drug's action on the CNS. Methyldopa is converted into the metabolite, alpha-methylnorepinephrine, in the CNS, where it stimulates the central inhibitory alpha-adrenergic receptors, leading to a reduction in sympathetic tone, total peripheral resistance, and blood pressure. Reduction in plasma renin activity, as well as the inhibition of both central and peripheral norepinephrine and serotonine production may also contribute to the drug's antihypertensive effect, although this is not a major mechanism of action. This is done through the inhibition of the decarboxylation of dihydroxyphenylalanine (dopa)ãthe precursor of norepinephrineãand of 5-hydroxytryptophan (5-HTP)ãthe precursor of serotoninãin the CNS and in most peripheral tissues.


Methyldopa is an aromatic-amino-acid decarboxylase inhibitor in animals and in man. Only methyldopa, the L-isomer of alpha-methyldopa, has the ability to inhibit dopa decarboxylase and to deplete animal tissues of norepinephrine. In man the antihypertensive activity appears to be due solely to the L-isomer. About twice the dose of the racemate (DL-alpha-methyldopa) is required for equal antihypertensive effect. Methyldopa has no direct effect on cardiac function and usually does not reduce glomerular filtration rate, renal blood flow, or filtration fraction. Cardiac output usually is maintained without cardiac acceleration. In some patients the heart rate is slowed. Normal or elevated plasma renin activity may decrease in the course of methyldopa therapy. Methyldopa reduces both supine and standing blood pressure. Methyldopa usually produces highly effective lowering of the supine pressure with infrequent symptomatic postural hypotension. Exercise hypotension and diurnal blood pressure variations rarely occur.


Hepatic, extensively metabolized. The known urinary metabolites are: a-methyldopa mono-0-sulfate; 3-0-methyl-a-methyldopa; 3, 4-dihydroxyphenylacetone; a-methyldopamine; 3-0-methyl-a-methyldopamine and their conjugates.


The oral LD50 of methyldopa is greater than 1.5 g/kg in both the mouse and the rat. Symptoms of overdose include bloating, constipation, diarrhea, dizziness, extreme drowsiness, gas, light-headedness, nausea, severely low blood pressure, slow heartbeat, vomiting, and weakness.

(2S)-2-amino-3-(3, 4-dihydroxyphenyl)-2-methylpropanoic acid
C02AB01 C02AB02
DB00968 (APRD01106)
Molecular Mass:
Alpha medopa Alphamethyldopa AMD L-Methyl Dopa _-methyl-L-dopa
AHFS Code:
General Reference:
General Reference:

  1. Mah GT, Tejani AM, Musini VM: Methyldopa for primary hypertension. Cochrane Database Syst Rev. 2009 Oct 7;(4):CD003893. Pubmed
  2. McCoy S, Baldwin K: Pharmacotherapeutic options for the treatment of preeclampsia. Am J Health Syst Pharm. 2009 Feb 15;66(4):337-44. Pubmed
  3. Sica DA: Centrally acting antihypertensive agents: an update. J Clin Hypertens (Greenwich). 2007 May;9(5):399-405. Pubmed
  4. van Zwieten PA: Development and trends in the drug treatment of essential hypertension. J Hypertens Suppl. 1992 Dec;10(7):S1-12. Pubmed
  5. Rosenthal T, Oparil S: The effect of antihypertensive drugs on the fetus. J Hum Hypertens. 2002 May;16(5):293-8. Pubmed
  6. van Zwieten PA, Timmermans PB: Pharmacology and characterization of central alpha-adrenoceptors involved in the effect of centrally acting antihypertensive drugs. Chest. 1983 Feb;83(2 Suppl):340-3. Pubmed
  7. van Zwieten PA: Pharmacology of centrally acting hypotensive drugs. Br J Clin Pharmacol. 1980;10 Suppl 1:13S-20S. Pubmed

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