DRUG INTERACTIONS
Drug Interactions
Methyldopa
When methyldopa is used with other antihypertensive drugs, potentiation of antihypertensive effect may occur. Patients should be followed carefully to detect side reactions or unusual manifestations of drug idiosyncrasy.
Patients may require reduced doses of anesthetics when on methyldopa. If hypotension does occur during anesthesia, it usually can be controlled by vasopressors. The adrenergic receptors remain sensitive during treatment with methyldopa.
Monoamine oxidase (MAO) inhibitors: See CONTRAINDICATIONS.
When methyldopa and lithium are given concomitantly the patient should be carefully monitored for symptoms of lithium toxicity. Read the prescribing information for lithium preparations.
Several studies demonstrate a decrease in the bioavailability of methyldopa when it is ingested with ferrous sulfate or ferrous gluconate. This may adversely affect blood pressure control in patients treated with methyldopa. Coadministration of methyldopa with ferrous sulfate or gluconate is not recommended.
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OVERDOSAGE
Acute overdosage may produce acute hypotension with other responses attributable to brain and gastrointestinal malfunction (excessive sedation, weakness, bradycardia, dizziness, light-headedness, constipation, distention, flatus, diarrhea, nausea, vomiting).
In the event of overdosage, symptomatic and supportive measures should be employed. When ingestion is recent, gastric lavage or emesis may reduce absorption. When ingestion has been earlier, infusions may be helpful to promote urinary excretion. Otherwise, management includes special attention to cardiac rate and output, blood volume, electrolyte balance, paralytic ileus, urinary function and cerebral activity.
Sympathomimetic drugs (e.g., norepinephrine, epinephrine, metaraminol bitartrate) may be indicated. Methyldopa is dialyzable. The degree to which hydrochlorothiazide is removed by hemodialysis has not been established.
The oral LD50 of methyldopa is greater than 1.5 g/kg in both the mouse and the rat. The oral LD50 of hydrochlorothiazide is greater than 10 g/kg in the mouse and rat.
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