Adults:PO 250 mg 2 to 3 times daily in the first 48 h initially, then 500 mg to 2 g/day (max, 3 g/day) in 2 to 4 divided doses. Adjust doses at intervals of not less than 2 days until adequate response is achieved. To minimize sedation, increase dosage in the evening. IV 250 to 500 mg every 6 h as needed (max, 1 g every 6 h).
Children:PO 10 mg/kg/day in 2 to 4 doses (max, 65 mg/kg/day or 3 g/day, whichever is less). IV 20 to 40 mg/kg/day in divided doses every 6 h (max, 65 mg/kg/day or 3 g/day, whichever is less).
May require reduced doses of anesthetics. Hypotension during anesthesia can be controlled by vasopressors because adrenergic receptors remain sensitive.
When methyldopa is used with other hypotensive agents, the hypotensive effect may be potentiated. Closely monitor the patient to detect adverse reactions or manifestations of idiosyncratic reactions.
Beta-blockers, nonselective (eg, propranolol)
May cause paradoxical hypertension (rare). Closely monitor for acute increases in BP. If an acute increase occurs, discontinuation of the beta-blocker and treatment with an alpha-adrenergic blocking agent (eg, phentolamine) may be needed.
Ferrous sulfate or gluconate
May decrease oral methyldopa absorption. Coadministration is not recommended.
May result in dementia or sedation. If adverse mental symptoms occur, discontinue one or both drugs.
BP-lowering effects of methyldopa may be potentiated. Central effects of levodopa in Parkinson disease may be potentiated. Monitor BP and for signs of toxicity. If either occurs, adjust the dose of either drug as needed.
May precipitate lithium toxicity. Closely monitor the patient for signs and symptoms of lithium toxicity and adjust the lithium dose as needed.
MAOIs (eg, phenelzine)
May lead to excessive sympathetic stimulation. Coadministration is contraindicated.
Serious elevations in BP may occur. Closely monitor BP. If hypertension occurs, discontinue one or both drugs.
Sympathomimetics (eg, norepinephrine)
May potentiate pressor effects of sympathomimetics and lead to hypertension. Monitor BP. If hypertension occurs, discontinuation of the sympathomimetic agent or treatment with an alpha-adrenergic blocking agent (eg, phentolamine) may be needed.
Additive hypotensive effects may occur. If coadministration cannot be avoided, closely monitor BP and adjust treatment as needed.
Absorption: Absorption following oral administration is variable and incompletely absorbed. Mean bioavailability is approximately 50%.
Distribution: Crosses the blood-brain and placental barriers, appears in cord blood and breast milk, and is approximately 8% protein bound.
Metabolism: Extensively metabolized to multiple metabolites. Approximately 17% appears in plasma as free methyldopa.
Excretion: Approximately 70% (oral) and approximately 49% (IV) is excreted in urine as methyldopa and its mono-O-sulfate conjugate; excretion is complete in 36 h after oral dose. The half-life is 1.8 h (oral) and 1.5 to 2.1 h (IV), and the renal Cl is approximately 130 mL/min (oral) and 156 mL/min (IV).