Drug Class Description

Generic Name

Drug Description

Presentation

Indications

In the treatment of hypertension.

Adult Dosage

General considerations: Methyldopa is largely excreted by the kidney, and patients with impaired renal function may respond to smaller doses.

Withdrawal of 'Aldomet' is followed by return of hypertension, usually within 48 hours. This is not complicated generally by an overshoot of blood pressure.

Therapy with 'Aldomet' may be initiated in most patients already on treatment with other antihypertensive agents by terminating these antihypertensive medications gradually, as required. Following such previous antihypertensive therapy, 'Aldomet' should be limited to an initial dose of not more than 500 mg daily and increased as required at intervals of not less than two days.

When methyldopa is given to patients on other antihypertensives the dose of these agents may need to be adjusted to effect a smooth transition.

When 500 mg of 'Aldomet' is added to 50 mg of hydrochlorothiazide, the two agents may be given together once daily.

Many patients experience sedation for two or three days when therapy with 'Aldomet' is started or when the dose is increased. When increasing the dosage, therefore, it may be desirable to increase the evening dose first.

Oral therapy - Adults: Initial dosage: Usually 250 mg two or three times a day, for two days.

Adjustment: Usually adjusted at intervals of not less than two days, until an adequate response is obtained. The maximum recommended daily dosage is 3 g.

Oral therapy - Children: initial dosage is based on 10 mg/kg of bodyweight daily in 2-4 oral doses. The daily dosage is then increased or decreased until an adequate response is achieved. The maximum dosage is 65 mg/kg or 3.0 g daily, whichever is less.

Use in the elderly: The initial dose in elderly patients should be kept as low as possible, not exceeding 250 mg daily; an appropriate starting dose in the elderly would be 125 mg b.d. increasing slowly as required, but not to exceed a maximum daily dosage of 2 g. Syncope in older patients may be related to an increased sensitivity and advanced arteriosclerotic vascular disease. This may be avoided by lower doses.

Child Dosage

Elderly Dosage

Contra Indications

'Aldomet' is contra-indicated in patients with:

• active hepatic disease, such as acute hepatitis and active cirrhosis

• hypersensitivity (including hepatic disorders associated with previous methyldopa therapy) to any component of these products

• depression

• on therapy with monoamine oxidase inhibitors (MAOIs).

'Aldomet' is not recommended for the treatment of phaeochromocytoma.

Special Precautions

Acquired haemolytic anaemia has occurred rarely; should symptoms suggest anaemia, haemoglobin and/or haematocrit determinations should be made. If anaemia is confirmed, tests should be done for haemolysis. If haemolytic anaemia is present, 'Aldomet' should be discontinued. Stopping therapy, with or without giving a corticosteroid, has usually brought prompt remission. Rarely, however, deaths have occurred.

Some patients on continued therapy with methyldopa develop a positive Coombs test. From the reports of different investigators, the incidence averages between 10% and 20%. A positive Coombs test rarely develops in the first six months of therapy, and if it has not developed within 12 months, it is unlikely to do so later on continuing therapy. Development is also doserelated, the lowest incidence occurring in patients receiving 1 g or less of methyldopa per day. The test becomes negative usually within weeks or months of stopping methyldopa.

Prior knowledge of a positive Coombs reaction will aid in evaluating a crossmatch for transfusion. If a patient with a positive Coombs reaction shows an incompatible minor crossmatch, an indirect Coombs test should be performed. If this is negative, transfusion with blood compatible in the major crossmatch may be carried out. If positive, the advisability of transfusion should be determined by a haematologist.

Reversible leucopenia, with primary effect on granulocytes has been reported rarely. The granulocyte count returned to normal on discontinuing therapy. Reversible thrombocytopenia has occurred rarely.

Occasionally, fever has occurred within the first three weeks of therapy, sometimes associated with eosinophilia or abnormalities in liver-function tests. Jaundice, with or without fever, also may occur. Its onset is usually within the first two or three months of therapy. In some patients the findings are consistent with those of cholestasis. Rare cases of fatal hepatic necrosis have been reported. Liver biopsy, performed in several patients with liver dysfunction, showed a microscopic focal necrosis compatible with drug hypersensitivity. Liver-function tests and a total and differential white blood-cell count are advisable before therapy and at intervals during the first six weeks to twelve weeks of therapy, or whenever an unexplained fever occurs.

Should fever, abnormality in liver function, or jaundice occur, therapy should be withdrawn. If related to methyldopa, the temperature and abnormalities in liver function will then return to normal. Methyldopa should not be used again in these patients. Methyldopa should be used with caution in patients with a history of previous liver disease or dysfunction.

Patients may require reduced doses of anaesthetics when on methyldopa. If hypotension does occur during anaesthesia, it can usually be controlled by vasopressors. The adrenergic receptors remain sensitive during treatment with methyldopa.

Dialysis removes methyldopa; therefore, hypertension may recur after this procedure.

Rarely, involuntary choreoathetotic movements have been observed during therapy with methyldopa in patients with severe bilateral cerebrovascular disease. Should these movements occur, therapy should be discontinued.

'Aldomet' should be used with extreme caution in patients, or in near relatives of patients, with hepatic porphyria.

Interference with laboratory tests:

Methyldopa may interfere with the measurement of urinary uric acid by the phosphotungstate method, serum creatinine by the alkaline picrate method, and AST (SGOT) by colorimetric method. Interference with spectrophotometric methods for AST (SGOT) analysis has not been reported.

As methyldopa fluoresces at the same wavelengths as catecholamines, spuriously high amounts of urinary catecholamines may be reported interfering with a diagnosis of phaeochromocytoma.

It is important to recognise this phenomenon before a patient with a possible phaeochromocytoma is subjected to surgery. Methyldopa does not interfere with measurements of VMA (vanillylmandelic acid) by those methods which convert VMA to vanillin.

Rarely, when urine is exposed to air after voiding, it may darken because of breakdown of methyldopa or its metabolites.

Interactions

Lithium:

When methyldopa and lithium are given concomitantly the patient should be monitored carefully for symptoms of lithium toxicity.

Other antihypertensive drugs:

When methyldopa is used with other antihypertensive drugs, potentiation of antihypertensive action may occur. The progress of patients should be carefully followed to detect side reactions or manifestations of drug idiosyncrasy.

Other classes of drug:

The antihypertensive effect of 'Aldomet' may be diminished by sympathomimetics, phenothiazines, tricyclic antidepressants and MAOIs. In addition, phenothiazines may have additive hypotensive effects.

Iron:

Several studies demonstrate a decrease in the bioavailability of methyldopa when it is ingested with ferrous sulphate or ferrous gluconate. This may adversely affect blood pressure control in patients treated with methyldopa.

Tricyclic antidepressants, phenothiazines, lithium, MAOIs, sympathomimetics. Other antihypertensives.

Adverse Reactions

The following reactions have been reported:

Cardiac disorders: Bradycardia, aggravation of angina pectoris, myocarditis, pericarditis.

Blood and lymphatic system disorders: Haemolytic anaemia, bone-marrow depression, leucopenia, granulocytopenia, thrombocytopenia, eosinophilia.

Nervous system disorders: Sedation (usually transient), headache, paraesthesia, Parkinsonism, Bell's palsy, involuntary choreoathetotic movements. impaired mental acuity, prolonged carotid sinus hypersensitivity. Dizziness, lightheadedness, and symptoms of cerebrovascular insufficiency (may be due to lowering of blood pressure).

Respiratory, thoracic and mediastinal disorders: Nasal stuffiness.

Gastrointestinal disorders: Nausea, vomiting, distension, constipation, flatus, diarrhoea, colitis, mild dryness of mouth, sore or 'black' tongue, pancreatitis.

Skin and subcutaneous tissue disorders: Rash as in eczema or lichenoid eruption, toxic epidermal necrolysis.

Musculoskeletal and connective tissue disorders: Lupuslike syndrome, mild arthralgia with or without joint swelling, myalgia.

Endocrine disorders: Hyperprolactinaemia.

Infections and infestations: Sialadenitis.

Vascular disorders: Orthostatic hypotension (decrease daily dosage).

General disorders and administrative site conditions: Asthenia or weakness, oedema (and weight gain) usually relieved by use of a diuretic. (Discontinue methyldopa if oedema progresses or signs of heart failure appear.), drug-related fever.

Hepatobiliary disorders: Liver disorders including hepatitis, jaundice.

Reproductive system and breast disorders: Breast enlargement, gynaecomastia, amenorrhoea, lactation, impotence, failure of ejaculation.

Psychiatric disorders: Psychic disturbances including nightmares, reversible mild psychoses or depression, decreased libido.

Investigations: Positive Coombs test, positive tests for antinuclear antibody, LE cells, and rheumatoid factor, abnormal liver-function tests, rise in blood urea.

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