Methyldopate hydrochloride [levo-3-(3,4-dihydroxyphenyl)-2-methylalanine, ethyl ester hydrochloride] is the ethyl ester of methyldopa, supplied as the hydrochloride salt with a molecular weight of 275.73. Methyldopate hydrochloride is more soluble and stable in solution than methyldopa and is the preferred form for intravenous use. Methyldopate hydrochloride is an alpha adrenergic agonist that has both central and peripheral nervous system effects. Its primary clinical use is as an antihypertensive agent.

D-Methyldopa is an inactive isomer of methyldopa. It is known, that only L-isomer has the ability to inhibit dopa decarboxylase and possesses the antihypertensive activity in man. Moreover, about twice the dose of the racemate (DL-form of methyldopa) is required for the equal antihypertensive effect.

3-O-methyldopa (3-OMD) is a metabolite of L-3,4-dihydroxyphenylalanine (L-DOPA), a drug used for the treatment of Parkinson's disease patients. 3-OMD is formed by catechol-O-methyltransferase. 3-OMD may be responsible for the side effects of L-DOPA.

Methyldopa is an aromatic-amino-acid decarboxylase inhibitor in animals and in man. Methyldopa is a medication that has been used to treat high blood pressure since the 1960s. Methyldopa is indicated in the treatment of moderate to severe hypertension, including that complicated by renal disease. Only methyldopa, the L-isomer of alpha-methyldopa, has the ability to inhibit dopa decarboxylase and to deplete animal tissues of norepinephrine. D-isomer is relatively inactive. In man the antihypertensive activity appears to be due solely to the L-isomer, which became generally known as methyldopa (Aldomet). About twice the dose of the racemate (Methyldopa anhydrous, (±)-; DL-alpha-methyldopa) is required for equal antihypertensive effect. Racemic alpha-methyldopa was shown to be much less effective or ineffective for the treatment of hypertension. The comparative study of the hypotensive effect of L-alpha-methyl-dopa (L-isomer) versus the racemic form was performed. The short-term hypotensive effects of the racemic form and the L-isomer of alpha-methyl-dopa were compared in 13 hospitalized patients with arterial hypertension. After a placebo period the active preparations in a fixed dose of 1.5 g daily were administered for three-day periods separated by a second placebo period of three days, the sequence of the active drugs being alternated. Both substances were shown to exert significant hypotensive effects. The L-isomer produced significant blood-pressure reductions irrespective of whether or not it was given first, whereas the racemic form was effective only when given first. The blood-pressure levels obtained with the L-isomer were throughout lower than those with the racemic form. Methyldopa is a centrally acting antihypertensive agent. It is metabolized to alpha-methylnorepinephrine in the brain, and this compound is thought to activate central alpha-2 adrenergic receptors