Nurses Compass
Drug Guide
Metyrosine
Classification
Therapeutic: Antihypertensive, Used in management of pheochromocytoma
Pharmacological: Tyrosine hydroxylase inhibitor
FDA Approved Indications
- Pheochromocytoma (to control hypertension before surgery)
Mechanism of Action
Metyrosine inhibits tyrosine hydroxylase, the enzyme involved in catecholamine synthesis, reducing the production of dopamine, norepinephrine, and epinephrine.
Dosage and Administration
Adult: Initial dose: 250 mg four times daily; titrate as needed up to 2 g/day, divided into four doses.
Pediatric: Data limited; use with caution, typically reserved for life-threatening conditions under specialist supervision.
Geriatric: Start at lower end of dosing range due to increased sensitivity; monitor closely.
Renal Impairment: Adjust dose cautiously; no specific guidelines, use clinical judgment.
Hepatic Impairment: Use with caution; no specific guideline, monitor for adverse effects.
Pharmacokinetics
Absorption: Well absorbed orally.
Distribution: Widely distributed, crosses blood-brain barrier.
Metabolism: Partially metabolized in the liver.
Excretion: Excreted primarily via the urine.
Half Life: Approximately 2-4 hours.
Contraindications
- History of hypersensitivity to metyrosine.
- Severe hepatic impairment.
Precautions
- Use with caution in patients with depression, as catecholamine depletion can exacerbate symptoms.
- Monitor for extrapyramidal symptoms and neuropsychiatric effects.
- Pregnancy: Data limited; potential risks vs benefit should be considered.
Adverse Reactions - Common
- Sedation or fatigue (Common)
- Gastrointestinal upset (nausea, vomiting) (Common)
- Dizziness (Common)
Adverse Reactions - Serious
- Neuropsychiatric effects (e.g., depression, hallucinations) (Less common)
- Extrapyramidal symptoms (Uncommon)
- Hematologic effects (e.g., leukopenia, agranulocytosis) (Rare)
Drug-Drug Interactions
- Levodopa (may reduce efficacy)
- Antipsychotics (potential interactions)
Drug-Food Interactions
N/ADrug-Herb Interactions
N/ANursing Implications
Assessment: Monitor blood pressure, neuropsychiatric status, and signs of adverse reactions.
Diagnoses:
- Risk for ineffective tissue perfusion related to hypotension
- Risk for injury related to sedation or orthostatic hypotension
Implementation: Administer with food to decrease GI upset, preferably at evenly spaced intervals.
Evaluation: Assess blood pressure response and monitor for adverse effects, neuropsychological status.
Patient/Family Teaching
- Take medication exactly as prescribed.
- Report any symptoms of depression, hallucinations, or unusual neuropsychiatric effects.
- Monitor blood pressure regularly.
- Be aware of potential sedative effects and avoid activities requiring alertness until response is known.
Special Considerations
Black Box Warnings:
- No specific black box warnings.
Genetic Factors: N/A
Lab Test Interference: May cause falsely elevated levels of plasma catecholamines.
Overdose Management
Signs/Symptoms: Sedation, hypotension, extrapyramidal symptoms, depression.
Treatment: Supportive care, activated charcoal if ingestion is recent, symptomatic treatment, and monitoring.
Storage and Handling
Storage: Store at room temperature, away from light and moisture.
Stability: Stable under recommended storage conditions.