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Methyldopa
Pronunciation
U.S. Brand Names
Generic Available
Canadian Brand Names
Synonyms
Pharmacological Index
Use
Pregnancy Risk Factor
Pregnancy/Breast-Feeding Implications
Contraindications
Warnings/Precautions
Adverse Reactions
Overdosage/Toxicology
Drug Interactions
Stability
Mechanism of Action
Pharmacodynamics/Kinetics
Usual Dosage
Dietary Considerations
Monitoring Parameters
Test Interactions
Cardiovascular Considerations
Mental Health: Effects on Mental Status
Mental Health: Effects on Psychiatric Treatment
Dental Health: Local Anesthetic/Vasoconstrictor Precautions
Dental Health: Effects on Dental Treatment
Patient Information
Nursing Implications
Dosage Forms
References

Pronunciation
(meth il DOE pa)

U.S. Brand Names
Aldomet®

Generic Available

Yes


Canadian Brand Names
Apo®-Methyldopa; Dopamet®; Medimet®; Novo-Medopa®; Nu-Medopa

Synonyms
Methyldopate Hydrochloride

Pharmacological Index

False Neurotransmitter


Use

Management of moderate to severe hypertension


Pregnancy Risk Factor

B


Pregnancy/Breast-Feeding Implications

Clinical effects on the fetus: Crosses the placenta. Hypotension reported. A large amount of clinical experience with the use of these drugs for the management of hypertension during pregnancy is available. Available evidence suggests safe use during pregnancy and breast-feeding.

Breast-feeding/lactation: Crosses into breast milk at extremely low levels. American Academy of Pediatrics considers compatible with breast-feeding.


Contraindications

Hypersensitivity to methyldopa or any component; active hepatic disease; liver disorders previously associated with use of methyldopa; on monoamine oxidase inhibitors; bisulfite allergy if using oral suspension or injectable


Warnings/Precautions

Monitor for hemolytic anemia, positive Coombs' test, and liver dysfunction. A diuretic may be needed for weight gain or edema management. Its CNS side effects prevent it from being used frequently. It is the drug of choice for treatment of hypertension in pregnancy. Do use oral suspension or injectable if bisulfite allergy.


Adverse Reactions

>10%: Cardiovascular: Peripheral edema

1% to 10%:

Central nervous system: Drug fever, mental depression, anxiety, nightmares, drowsiness, headache

Gastrointestinal: Dry mouth

<1% (Limited to important or life-threatening symptoms): Orthostatic hypotension, bradycardia (sinus), sodium retention, sexual dysfunction, gynecomastia, hyperprolactinemia, thrombocytopenia, hemolytic anemia, positive Coombs' test, leukopenia, transient leukopenia or granulocytopenia, cholestasis or hepatitis and heptocellular injury, increased liver enzymes, jaundice, cirrhosis, dyspnea, SLE-like syndrome


Overdosage/Toxicology

Symptoms of overdose include hypotension, sedation, bradycardia, dizziness, constipation or diarrhea, flatus, nausea, vomiting

Hypotension usually responds to I.V. fluids, Trendelenburg positioning, or vasoconstrictors. Treatment is primarily supportive and symptomatic; can be removed by hemodialysis.


Drug Interactions

Iron supplements can interact and cause a significant increase in blood pressure.

Barbiturates and TCAs may reduce response to methyldopa.

Beta-blockers, MAO inhibitors, phenothiazines, and sympathomimetics: Hypertension, sometimes severe, may occur.

Lithium: Methyldopa may increase lithium toxicity; monitor lithium levels.

Tolbutamide, haloperidol, anesthetics, and levodopa effects/toxicity are increased with methyldopa.


Stability

Injectable dosage form is most stable at acid to neutral pH; stability of parenteral admixture at room temperature (25°C): 24 hours; stability of parenteral admixture at refrigeration temperature (4°C): 4 days; standard diluent: 250-500 mg/100 mL D5W


Mechanism of Action

Stimulation of central alpha-adrenergic receptors by a false transmitter that results in a decreased sympathetic outflow to the heart, kidneys, and peripheral vasculature


Pharmacodynamics/Kinetics

Peak hypotensive effect: Oral, parenteral: Within 3-6 hours

Duration: 12-24 hours

Distribution: Crosses the placenta; appears in breast milk

Protein binding: <15%

Metabolism: Intestinally and in the liver

Half-life: 75-80 minutes; End-stage renal disease: 6-16 hours

Elimination: Most (85%) metabolites appearing in the urine within 24 hours


Usual Dosage

Children:

Oral: Initial: 10 mg/kg/day in 2-4 divided doses; increase every 2 days as needed to maximum dose of 65 mg/kg/day; do not exceed 3 g/day.

I.V.: 5-10 mg/kg/dose every 6-8 hours up to a total dose of 65 mg/kg/24 hours or 3 g/24 hours

Adults:

Oral: Initial: 250 mg 2-3 times/day; increase every 2 days as needed; usual dose 1-1.5 g/day in 2-4 divided doses; maximum dose: 3 g/day.

I.V.: 250-500 mg every 6-8 hours; maximum dose: 1 g every 6 hours

Dosing interval in renal impairment:

Clcr >50 mL/minute: Administer every 8 hours.

Clcr 10-50 mL/minute: Administer every 8-12 hours.

Clcr <10 mL/minute: Administer every 12-24 hours.

Hemodialysis: Slightly dialyzable (5% to 20%)


Dietary Considerations

Avoid natural licorice (causes sodium and water retention and increases potassium loss); dietary requirements for vitamin B12 and folate may be increased with high doses of methyldopa


Monitoring Parameters

Blood pressure, standing and sitting/lying down, CBC, liver enzymes, Coombs' test (direct); blood pressure monitor required during I.V. administration


Test Interactions

Methyldopa interferes with the following laboratory tests: urinary uric acid, serum creatinine (alkaline picrate method), AST (colorimetric method), and urinary catecholamines (falsely high levels)


Cardiovascular Considerations

Methyldopa is not routinely used for the treatment of essential hypertension. However, it is still used in the management of pregnancy-associated hypertension. Although the drug crosses the placenta and may cause hypotension, there is a large body of experience using this drug in the treatment of pregnancy-associated hypertension. Overall, the medication appears to be safe during pregnancy and lactation. Important side effects to note are hemolytic anemia, drowsiness, and depression.


Mental Health: Effects on Mental Status

May cause drowsiness, dizziness, anxiety, nightmares, or depression


Mental Health: Effects on Psychiatric Treatment

Contraindicated with MAOIs; may rarely cause leukopenia; use caution with clozapine and carbamazepine; associated with lithium toxicity; use alternative antihypertensive agent; methyldopa may interact with psychotropics; monitor blood pressure and clinical status


Dental Health: Local Anesthetic/Vasoconstrictor Precautions

No information available to require special precautions


Dental Health: Effects on Dental Treatment

Anticholinergic side effects can cause a reduction of saliva production or secretion. This may result in discomfort and dental disease (ie, caries, oral candidiasis and periodontal disease)


Patient Information

Take as directed. Do not skip dose or discontinue without consulting prescriber. Follow recommended diet and exercise program. Do not use OTC medications which may affect blood pressure (eg, cough or cold remedies, diet pills, stay-awake medications) without consulting prescriber. This medication may cause altered color of urine (normal); drowsiness, dizziness, or impaired judgment (use caution when driving or engaging in tasks that require alertness until response to drug is known); postural hypotension (use caution when rising from sitting or lying position or when climbing stairs); or dry mouth or nausea (frequent mouth care or sucking lozenges may help). Report altered CNS status (eg, nightmares, depression, anxiety, increased nervousness); sudden weight gain (weigh yourself in the same clothes at the same time of day once a week); unusual or persistent swelling of ankles, feet, or extremities; palpitations or rapid heartbeat; persistent weakness, fatigue, or unusual bleeding; or other persistent side effects.


Nursing Implications

Transient sedation or depression may be common for first 72 hours of therapy; usually disappears over time; infuse over 30 minutes; assist with ambulation


Dosage Forms

Injection, as methyldopate hydrochloride: 50 mg/mL (5 mL, 10 mL)

Suspension, oral: 250 mg/5 mL (5 mL, 473 mL)

Tablet: 125 mg, 250 mg, 500 mg


References

Johnston GD and Smith AM, "Management of Overdose Due to Antihypertensive Agents," Adverse Drug React Acute Poisoning Rev, 1990, 9(2):75-89.

Shnaps Y, Almog S. Halkin H, et al, "Methyldopa Poisoning," J Toxicol Clin Toxicol, 1982, 19(5):501-3.


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