Methyldopa produces its antihypertensive effect by acting on the alpha adrenoceptors in the vasomotor center of the brain.though it is sympathomimetic drug they can cause decreased activity of the sympathetic nervous system to the cardiovascular system by acting as an agonist on the alpha-adrenoceptors, leading to falling in blood pressure.
- Methyldopa when given orally or parenterally, passes into the brain by an active process.it is converted in the brain into alpha methyldopa>>>alpha methyldopamine>>>alpha methyl noradrenaline.Alpha methyl noradrenaline then acts on alpha adrenoceptors in the vasomotor center of the brain and inhibit the sympathetic outflow to the peripheral tissues, especially CVS.Methyldopa produces its antihypertensive effects by causing reduction of peripheral vascular resistance.
- It is one of the safest antihypertensive drug in Pregnancy.
- Its maximum antihypertensive effect occurs in 4-6hoirs and then persist for about 24hours.
Absorption of methyldopa after oral administration is incomplete and its bioavailability after oral administration is about 25%.Most of the drug is excreted unchanged in the urine i.e about two third and the remaining is metabolized in the liver.its dosage should be reduced in renal and hepatic failure.
Methyldopa Adverse effects:
- The Most common side effects related tothis drug are the following; Sedation, Dizziness, Dry mouth and postural hypotension.
- Other less common adverse effects include anxiety, blurred vision, sleep disturbances, parkinsonism, and impotence.
- More serious but rare adverse effects are hemolytic anemia, hepatitis, thrombocytopenia, leukopenia, and a lupus erythematosus-like syndrome.Hepatitis with methyldopa is usually reversible when the drug is stopped .it usually occurs during the initial two months of therapy, but sometimes it can occur after a prolonged therapy with the drug.
A dose of 500-2000mg daily in a single or 2-3 divided doses orally .injection of methyldopa is available as 5 ml ampoules containing 50mg/ml.
A dose of 250-500mg by IV infusion and can be repeated after every six hours.