[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Adrenergic neuron blockers](https://durgical.com/en/pharmacology/classes/adrenergic-neuron-blockers/) › Metirosine (metyrosine)

# 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.

Updated Nov 12, 2026

Also called: metyrosine, alpha-methyl-para-tyrosine

## Quick facts

**Group**
[Adrenergic neuron blockers](https://durgical.com/en/pharmacology/classes/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.

On this page

- The basics Mechanism of action
- Indications
- Adverse effects
- Pharmacokinetics
- Memory aid

- Safety Contraindications
- Key interactions
- What is monitored
- Administration and safety
- Pregnancy and breastfeeding
- Nursing care

- Study Test yourself

- Connections Connections

## Mechanism of action

✂**Tyrosine hydroxylase**Metirosine (metyrosine)

ⓘ The figure shows the catalytic domain of human tyrosine hydroxylase, the enzyme metirosine inhibits; no structure with metirosine bound is available.

**Target in 3D:** Tyrosine hydroxylase. PDB structure 2XSN (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/2XSN) · Drag to rotate · pinch to zoom

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 →](https://durgical.com/en/conditions/phaeochromocytoma/)
- Phaeochromocytoma when surgery is not possible, and long-term control of malignant tumours [Phaeochromocytoma →](https://durgical.com/en/conditions/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

### Serious (rare, important)

- Extrapyramidal signs such as drooling, tremor and speech problems
- Crystals in the urine (crystalluria)
- Life-threatening arrhythmias and hypertensive crises can still occur during surgery on the tumour

## 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.

## Memory aid

METirosine stops the METabolic start line: no tyrosine hydroxylase, no DOPA, no catecholamines.

## 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.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/metirosine/)

[More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology)

## Connections

## Related drugs 3

- [Phenoxybenzamine](https://durgical.com/en/pharmacology/phenoxybenzamine/)
- [Reserpine](https://durgical.com/en/pharmacology/reserpine/)
- [Phentolamine](https://durgical.com/en/pharmacology/phentolamine/)

## Related conditions 1

- [Phaeochromocytoma](https://durgical.com/en/conditions/phaeochromocytoma/)

[← Back to the class: Adrenergic neuron blockers](https://durgical.com/en/pharmacology/classes/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](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=027f02b1-be49-4822-91a5-6cd66b56c0e1) (DailyMed (U.S. National Library of Medicine), 2026); [Crystal Structure of Human Tyrosine Hydroxylase Catalytic Domain](https://www.rcsb.org/structure/2XSN) (RCSB Protein Data Bank, 2010); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=C02KB01) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/metirosine/