[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Alpha blockers](https://durgical.com/en/pharmacology/classes/alpha-blockers/) › Phentolamine

[Pharmacology](https://durgical.com/en/pharmacology/) · [Alpha blockers](https://durgical.com/en/pharmacology/classes/alpha-blockers/)

# Phentolamine

A short-acting, reversible alpha blocker given by injection: the antidote when norepinephrine leaks from a vein, and a control for pheochromocytoma crises.

Updated 2026-11-01

- Class: [Alpha blockers](https://durgical.com/en/pharmacology/classes/alpha-blockers/)
- Receptor: Alpha-1 and alpha-2 adrenergic receptors
- ATC code: C04AB01

◎**Alpha-1 and alpha-2 adrenergic receptors**Phentolamine

ⓘ No structure of phentolamine bound to an alpha receptor is available; the figure shows doxazosin, another alpha blocker, in the binding site of the human alpha-1A adrenergic receptor.

**Target in 3D:** Alpha-1 and alpha-2 adrenergic receptors. PDB structure 9M4Q (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/9M4Q) · Drag to rotate · pinch to zoom

## Mechanism of action

Phentolamine competitively and reversibly blocks alpha-1 and alpha-2 receptors. Vessels dilate and blood pressure falls; blocking presynaptic alpha-2 receptors increases norepinephrine release, which, with the baroreflex, causes marked tachycardia. Injected into tissue where a vasopressor has leaked, it reverses the local vasoconstriction.

- Phentolamine competitively blocks alpha-1 and alpha-2 receptors
- Vessels dilate and blood pressure falls
- Alpha-2 block increases norepinephrine release: tachycardia
- Local injection reverses vasopressor-induced ischaemia

## Pharmacokinetics

**Half-life**
About 19 minutes after intravenous injection (label)

**Onset and duration**
Rapid after intravenous or local injection

## Indications

- Prevention or control of hypertensive episodes in pheochromocytoma, for example during surgery [Phaeochromocytoma →](https://durgical.com/en/conditions/phaeochromocytoma/)
- Prevention or treatment of skin necrosis after norepinephrine extravasation
- Phentolamine test for pheochromocytoma (now largely replaced by biochemical tests) [Phaeochromocytoma →](https://durgical.com/en/conditions/phaeochromocytoma/)

## Adverse effects

### Common

- Hypotension and orthostatic hypotension
- Tachycardia and arrhythmias
- Weakness, dizziness and flushing
- Nasal stuffiness
- Nausea, vomiting and diarrhoea

### Serious (rare, important)

- Myocardial infarction, cerebrovascular spasm or occlusion, usually after marked hypotension
- Prolonged severe hypotension

## Contraindications

- Myocardial infarction, past or present
- Coronary insufficiency, angina or other coronary artery disease
- Hypersensitivity to phentolamine

## Key interactions

**Other antihypertensives and vasodilators**
Additive hypotension

**Epinephrine**
The pressor effect is weakened and can reverse to hypotension

## What is monitored

- Blood pressure and heart rate closely after systemic use
- ECG in people with heart disease
- Skin colour and perfusion of the area treated for extravasation

## Administration and safety

- For extravasation, it is infiltrated through a fine needle into the blanched, ischaemic area as early as possible; it works best within the first hours.
- Reconstitute the powder only with the diluent the product specifies and use it promptly.
- Effective local treatment shows as immediate warming and reddening of the blanched skin.

## Nursing care

- Have phentolamine available wherever vasopressor infusions run.
- After systemic use, check blood pressure and heart rate often; keep the patient lying down, legs raised if pressure falls.
- Report chest pain, palpitations or neurological symptoms.
- After local use, mark and recheck the area for colour, warmth and capillary refill.

## Pregnancy and breastfeeding

Human data are limited; it is used if the benefit justifies the risk, for example in a pheochromocytoma crisis.

## Memory aid

PHENTOLAMINE: Puts out the fire of a leaked pressor: Pale skin turns PINK.

## Test yourself

Think of the answer, then tap the question to see it.

## What is phentolamine's role when a norepinephrine infusion extravasates?

It is infiltrated into the area to block alpha receptors and reverse the local vasoconstriction, preventing necrosis and sloughing.

## Why does phentolamine cause more tachycardia than prazosin?

It also blocks presynaptic alpha-2 receptors, which increases norepinephrine release onto cardiac beta-1 receptors, on top of the baroreflex.

## Which heart conditions contraindicate phentolamine?

Myocardial infarction (current or past), angina, coronary insufficiency or other coronary artery disease.

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

## Related drugs

- [Phenoxybenzamine](https://durgical.com/en/pharmacology/phenoxybenzamine/)
- [Norepinephrine](https://durgical.com/en/pharmacology/norepinephrine/)
- [Dopamine](https://durgical.com/en/pharmacology/dopamine/)

## Related conditions

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

[← Back to the class: Alpha blockers](https://durgical.com/en/pharmacology/classes/alpha-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: [DailyMed - PHENTOLAMINE MESYLATE injection, powder, for solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ed6c506c-5535-4b7c-ae1a-d63f09d796c9) (DailyMed (U.S. National Library of Medicine), 2024); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=C04AB01) (WHO Collaborating Centre for Drug Statistics Methodology, 2026); Farmacología básica y clínica (Katzung), cap. 10 (McGraw Hill, 2025).

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Representative model, for educational purposes only.

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