[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Vasopressors and inotropes](https://durgical.com/en/pharmacology/classes/vasopressors-and-inotropes/) › Phenylephrine

[Pharmacology](https://durgical.com/en/pharmacology/) · [Vasopressors and inotropes](https://durgical.com/en/pharmacology/classes/vasopressors-and-inotropes/)

# Phenylephrine

A pure alpha-1 agonist that tightens vessels. Given intravenously for low blood pressure during anaesthesia; it typically slows the heart by reflex.

Updated 2026-11-01

- Class: [Vasopressors and inotropes](https://durgical.com/en/pharmacology/classes/vasopressors-and-inotropes/)
- Receptor: Alpha-1 adrenergic receptor
- ATC code: C01CA06

## ⚠ High-alert medication

An error with this medicine can cause serious harm: double checks and protocols are used.

◎**Alpha-1 adrenergic receptor**Phenylephrine

ⓘ No structure of phenylephrine bound to its receptor is available; the figure shows noradrenaline in the same binding site of the human alpha-1A adrenergic receptor.

**Target in 3D:** Alpha-1 adrenergic receptor. PDB structure 7YMH (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/7YMH) · Drag to rotate · pinch to zoom

## Mechanism of action

Phenylephrine selectively stimulates alpha-1 receptors, constricting arterioles and veins in most vascular beds, including renal, splanchnic and pulmonary arteries. Blood pressure rises; the baroreflex increases vagal tone and slows the heart, so cardiac output can fall. Locally it also dilates the pupil and shrinks nasal mucosa.

- Phenylephrine stimulates vascular alpha-1 receptors
- Arterioles and veins constrict; blood pressure rises
- The baroreflex slows the heart (reflex bradycardia)

## Pharmacokinetics

**Distribution**
Large volume of distribution into organs and tissues

**Metabolism**
Mainly by MAO and sulfotransferase; it is not a catechol, so COMT does not inactivate it

**Half-life**
Effective half-life about 5 minutes after infusion (label)

## Indications

- Clinically important hypotension from vasodilation during anaesthesia
- Other forms: nasal decongestant, short-acting mydriatic for eye examination

## Adverse effects

### Common

- Nausea, vomiting and headache
- Reflex bradycardia
- Hypertension
- Reduced cardiac output

### Serious (rare, important)

- Severe bradycardia
- Peripheral and visceral ischaemia
- Skin necrosis after extravasation
- Worsening of angina, heart failure or pulmonary arterial hypertension
- Greater need for kidney replacement therapy in septic shock

## Contraindications

- None listed on the label; caution in severe heart disease

## Key interactions

**MAO inhibitors, tricyclic antidepressants, oxytocic drugs, atropine and ergot alkaloids**
Stronger pressor effect; with oxytocics, risk of haemorrhagic stroke

**Alpha blockers, PDE-5 inhibitors, calcium channel blockers and ACE inhibitors**
Weaker pressor effect

## What is monitored

- Blood pressure and heart rate continuously
- Peripheral perfusion
- Kidney function in septic shock
- Infusion site

## Administration and safety

- Intravenous bolus or infusion after dilution, by trained staff with continuous monitoring.
- Check the infusion site often for free flow; extravasation can cause necrosis.
- Concentrations differ between products: check the label before preparing it.
- In end-stage kidney disease patients may respond more strongly.

## Nursing care

- Check heart rate as well as blood pressure: a slow heart is an expected reflex but can be severe.
- Watch the colour and temperature of the limbs and the infusion site.
- Report chest pain, breathlessness or falling urine output.

## Pregnancy and breastfeeding

Studies during caesarean section have not shown a risk of birth defects, and it does not appear to affect fetal heart rate much at usual doses.

## Memory aid

PHENYLephrine: Pure alpha-1, Pressure up, Pulse down.

## Test yourself

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

## Why does phenylephrine often slow the heart?

The rise in blood pressure from pure alpha-1 vasoconstriction activates the baroreflex, increasing vagal tone (reflex bradycardia).

## In what clinical setting is intravenous phenylephrine mainly used?

Hypotension from vasodilation during anaesthesia, for example after spinal anaesthesia.

## Which drugs weaken the pressor effect of phenylephrine?

Alpha blockers, PDE-5 inhibitors, calcium channel blockers, ACE inhibitors and central sympatholytics, among others.

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

## Related drugs

- [Norepinephrine](https://durgical.com/en/pharmacology/norepinephrine/)
- [Ephedrine](https://durgical.com/en/pharmacology/ephedrine/)
- [Midodrine](https://durgical.com/en/pharmacology/midodrine/)

[← Back to the class: Vasopressors and inotropes](https://durgical.com/en/pharmacology/classes/vasopressors-and-inotropes/)

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 - PHENYLEPHRINE HYDROCHLORIDE injection](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c7026b15-1228-4acb-beed-4474fcdbb972) (DailyMed (U.S. National Library of Medicine), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=C01CA06) (WHO Collaborating Centre for Drug Statistics Methodology, 2026); Farmacología básica y clínica (Katzung), cap. 9 (McGraw Hill, 2025).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

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