After oral administration bioavailability is low because of extensive metabolism.
HYPERTENSION OF ALL GRADES, HYPERTENSION ASSOCIATED WITH DIABETES AND PREGANANCY, CHILDREN AND ADOLESCENTS: 250mg 2-3 times a day. After 48 hrs dose changes every 48 hrs until optimum response is obtained. Maintenance usually 250-500mg b.i.d. Daily max 3g. Children: 10mg/kg/day in 2-4 divided doses.
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.
Haloperidol: adverse mental symptoms and high incidence of sedation.
Levodopa: Effects of levodopa potentiated.
Corticosteroids & Carbenoxolone: ANtagonism of hypotensive effects.
Propranolol: Paradoxical hypertensive effect.
Diuretics: Enhaced hypotensive effect.
Nitrates: Enhaced hypotensive effect.
Sympathomimetics: Methyldopa potentiates the pressor effects.
Antipsychotics: Increased risk of extrapyramidal symptoms.
Tolbutamide: Hypoglycaemic effects enhanced.
Sex hormones: Antagonise hypotensive effects.
Lab test: Interferes with tests for urinary uric acid by phosphotung- state method. Serum creatinine by alkaline picrate method.
AST high levels of urinary catecholamines occur interfering with diagnosis of pheochromocytoma.
Effect & Precaution
Dizziness, postural hypotension, sedation, dry mouth, headache, sleep disturbance, depression, anxiety, impotence, blurred vision, constipation, skin rash, arthralgia, fatigue, anorexia, haemolytic anemia, Parkinsonian signs, drug fever, hepatitis,
Precaution: Renal dysfunction, acquired haemolytic anemia, patients may show +ve direct Coomb’s test.
Pregnancy: may be used.
Breast Feeding: May be used.
Man: May be used with caution.