Source: Medicines & Healthcare Products Regulatory Agency (GB) Revision Year: 2019 Publisher: Intrapharm Laboratories Limited, The Courtyard Barns, Choke Lane, Cookham Dean, Maidenhead, Berkshire, SL6 6PT
Methyldopa is an antihypertensive agent acting centrally by stimulating alpha adrenergic receptors. It inhibits the decarboxylation of dopa to dopamine but this action is not responsible for the hypotensive effect. It is suggested that a metabolite, alpha methylnoradrenaline may act as a false transmitter in the CNS. It reduces tissue concentration of dopamine noradrenaline, adrenaline and serotonin.
Methyldopa is incompletely absorbed from the gastrointestinal tract. Methyldopa is extensively metabolised through pathways common to the catecholamines utilising dopa decarboxylates and dopamine B-hydroxylase.
Decarboxylation is stereospecific. The bioavailability of an oral dose averages 25% (±16%) and peak plasma levels occur 2 to 3 hours later. Elimination is biphasic. It is partly conjugated mainly to the o-sulphate and is excreted by the kidneys.
The elimination half-life is 1.8 ± 0.2 hours, methyldopa has been shown to cross the placental barrier and is found in the lungs, heart and muscles after 24 hours, detectable quantities are present in the liver and kidneys.
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