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Pharmacology: Pharmacokinetics: Methyldopa is variably and incompletely absorbed after oral administration, apparently by an amino acid active transport system. The mean bioavailability has been reported to be about 50%. It is extensively metabolized and is excreted in urine mainly as unchanged drug and the O-sulfate conjugate. It crosses the blood-brain barrier and is decarboxylated in the CNS to active alpha-methylnoradrenaline.
The elimination is biphasic with a half-life of about 1.7 hours in the initial phase; the second phase is more prolonged. Clearance is decreased and half-life prolonged in renal impairment. Plasma protein binding is reported to be minimal. Methyldopa crosses the placenta; small amounts are distributed into breast milk.
