Methyldopa

Methyldopa is a drug used to lower blood pressure in people with hypertension (high blood pressure). Methyldopa lowers blood pressure by decreasing the levels of certain chemicals in your blood. This allows your blood vessels (veins and arteries) to relax (widen) and your heart to beat more slowly and easily. Methyldopa is an aromatic-amino-acid decarboxylase inhibitor in man. It lowers arterial blood pressure by stimulation of central inhibitory alpha-adrenergic receptors, false neurotransmission, and/or reduction of plasma renin activity. A net reduction in the tissue concentration of serotonin, dopamine, adrenaline and noradrenaline has been noted.

Methyldopa acts upon certain areas of the central nervous system (the brain and spinal cord) that regulate the activity of the heart and the smooth muscle tissue surrounding the arteries. The drug causes blood vessels to relax and widen, which in turn lowers blood pressure. Methyldopa is metabolised in cnetral noradrenergic neurones to alphamethyl NA. This is a specific agonist for alpha2 receptors, sympathetic tone is reduced as is blood pressure. Methyldopa is incompletely absorbed from the gastrointestinal tract achieving peak plasma concentrations (approx. 3.3 µg/mL) about two to three hours after administration of a 500mg dose. Plasma protein binding is minimal and the methyldopa appears to distribute extravascularly. Methyldopa crosses the placenta and small amounts appear in breast milk mostly in the conjugated form. Elimination involves partial conjugation to the O-Sulphate with excretion of this conjugate and unchanged medicine in the urine. It follows a biphasic pattern with the µ-phase half-life ranging from 0.74-1.10h and the b-phase half-life ranging from 8.0-65.0h.

Methyldopa is used to treat hypertension (high blood pressure). It may also be used for purposes other than those listed in this medication guide. Methyldopa has no direct effect on cardiac function and usually does not reduce glomerular filtration rate, renal blood flow or filtration fraction.