Metirosine (metyrosine)
Adrenergic neuron blockers
Adrenergic neuron blockers
A capsule that blocks the first step of catecholamine synthesis. Used to prepare or control patients with phaeochromocytoma, not for ordinary hypertension.
Also called: metyrosine, alpha-methyl-para-tyrosine
Quick facts
- Group
- Adrenergic neuron blockers
- Target
- Tyrosine hydroxylase
- Used for
- Phaeochromocytoma
- Key effects
- Sedation · Diarrhoea · Anxiety
- Monitor
- Blood pressure and heart rhythm · Urine catecholamines
- ATC
- C02KB01
No doses: the clinician sets them by the current guideline.
Mechanism of action
The figure shows the catalytic domain of human tyrosine hydroxylase, the enzyme metirosine inhibits; no structure with metirosine bound is available.
Tyrosine hydroxylase turns tyrosine into DOPA, the rate-limiting step in making dopamine, noradrenaline and adrenaline. Metirosine, a tyrosine analogue, inhibits this enzyme, so the tumour and the nerves make fewer catecholamines. In phaeochromocytoma this lowers blood pressure and the frequency of attacks. Because it also lowers brain dopamine, sedation and extrapyramidal signs are common.
- Metirosine inhibits tyrosine hydroxylase
- Less tyrosine becomes DOPA
- Less dopamine, noradrenaline and adrenaline are made
- Blood pressure and attacks fall; brain dopamine falls too
Indications
- Phaeochromocytoma: preparation for surgery Phaeochromocytoma →
- Phaeochromocytoma when surgery is not possible, and long-term control of malignant tumours Phaeochromocytoma →
Adverse effects
Common
- Sedation, most marked at the start
- Diarrhoea
- Anxiety, confusion, depression or hallucinations
- Breast swelling, milk discharge and impotence (infrequent)
- Insomnia and restlessness after stopping
Contraindications
- Known hypersensitivity to metirosine
- Not used for essential (primary) hypertension
Key interactions
- Phenothiazines or haloperidol
- More extrapyramidal effects, because all lower dopamine signalling.
- Alcohol and other CNS depressants
- Additive sedation.
What is monitored
- Blood pressure and heart rhythm, continuously during surgery
- Urine catecholamines and metanephrines to judge the effect
- Urine checks for crystals; fluid intake
- Sedation and movement problems
Administration and safety
- Oral capsule; usually added to alpha-blockade before surgery.
- Plenty of fluid is drunk every day to keep urine flowing and prevent crystals.
- Intravascular volume is kept up during and after surgery to avoid hypotension.
Pregnancy and breastfeeding
No animal reproduction studies have been done; it is used in pregnancy only if clearly needed.
Nursing care
- Before: record blood pressure, pulse and baseline mental state.
- During: watch for drowsiness, drooling, tremor or confusion and report them.
- Track fluid intake and urine output; report cloudy urine.
- Teach to avoid alcohol and driving until the sedative effect is known.
Pharmacokinetics
- Absorption
- Well absorbed by mouth.
- Elimination
- Most of the drug is excreted unchanged in the urine; it can crystallise there.
Test yourself
Think of the answer, then tap the question to see it.
Which enzyme does metirosine inhibit, and why does that matter?
Tyrosine hydroxylase, the rate-limiting step of catecholamine synthesis, so the tumour makes less noradrenaline and adrenaline.
Why are sedation and parkinsonian signs common with metirosine?
It also lowers dopamine synthesis in the brain.
Why is a high fluid intake encouraged during treatment?
The drug is excreted largely unchanged in the urine and can form crystals.
Connections
← Back to the class: Adrenergic neuron blockers
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: METYROSINE capsule (DailyMed (U.S. National Library of Medicine), 2026); Crystal Structure of Human Tyrosine Hydroxylase Catalytic Domain (RCSB Protein Data Bank, 2010); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.