Pharmacology · Vasopressors and inotropes

Epinephrine !

Adrenaline: the first medicine for anaphylaxis, given into the thigh muscle. By infusion it also supports blood pressure in septic shock.

Updated 2026-11-01

Class: Vasopressors and inotropes
Receptor: Alpha and beta adrenergic receptors (beta-2 shown)
ATC code: C01CA24
WHO Model List of Essential Medicines

Also called: Adrenaline

Alpha and beta adrenergic receptors (beta-2 shown)Epinephrine

The figure shows epinephrine bound to the human beta-2 adrenergic receptor, stabilised by a nanobody in the active state.

Target in 3D: Alpha and beta adrenergic receptors (beta-2 shown). PDB structure 4LDO (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

Epinephrine stimulates alpha and beta receptors. Alpha-1 constricts vessels and reduces mucosal oedema; beta-1 increases the force and rate of the heartbeat; beta-2 relaxes bronchial smooth muscle and reduces the release of mediators from mast cells. In anaphylaxis these actions reverse hypotension, airway swelling and bronchospasm together.

Epinephrine activates alpha and beta adrenergic receptors
Alpha-1: vasoconstriction and less mucosal oedema
Beta-1: stronger, faster heartbeat
Beta-2: bronchodilation and fewer mast-cell mediators

Pharmacokinetics

Absorption: Intramuscular injection into the thigh is absorbed quickly; poor oral bioavailability
Metabolism: Rapidly inactivated by COMT and MAO
Half-life: Effective half-life under 5 minutes after intravenous use (label)
Onset and duration: Fast; a steady state is reached soon after an infusion starts

Indications

Anaphylaxis and other severe type I allergic reactions Anaphylaxis →
Hypotension in septic shock (infusion) Sepsis and septic shock →
Cardiac arrest (resuscitation protocols)

Adverse effects

Common

Anxiety, restlessness and tremor
Palpitations and tachycardia
Pallor, sweating and headache
Nausea and vomiting
Hyperglycaemia and raised lactate

Contraindications

None absolute in anaphylaxis: the label lists no contraindications

Key interactions

Beta blockers (for example propranolol): Listed among drugs that potentiate epinephrine and raise the risk of arrhythmias; with non-selective blockers the alpha effect acts unopposed
MAO inhibitors and tricyclic antidepressants: Severe, prolonged hypertension
Halogenated anaesthetics, digoxin and diuretics: Higher risk of arrhythmias
Alpha blockers, nitrates and other vasodilators: Weaker pressor effect

What is monitored

Blood pressure, heart rate and rhythm
Respiratory status and oxygen saturation in anaphylaxis
Glucose and lactate during infusions

Administration and safety

Anaphylaxis: intramuscular injection into the anterolateral thigh, through clothing if needed; not into the buttock, fingers, hands or feet.
Epinephrine comes in several strengths and forms for intramuscular or intravenous use: check the label and route carefully before giving it.
Infusions: diluted, by pump, preferably through a central or large vein; check the site often for blanching or extravasation.
Do not use the solution if it is coloured, cloudy or has particles.
Epinephrine and ephedrine have look-alike names: read the label twice.

Nursing care

In anaphylaxis, epinephrine is not delayed: it is the first-line medicine, and antihistamines do not replace it.
Monitor blood pressure, heart rate, breathing and oxygen saturation; symptoms can return after the first response.
During infusions, watch ECG, glucose and the infusion site; wean gradually.
Teaching: people with prescribed auto-injectors learn when and how to use them and to seek emergency care afterwards.

Pregnancy and breastfeeding

Anaphylaxis and septic shock threaten mother and fetus, so epinephrine is used when needed; it can constrict uterine vessels and reduce uterine blood flow.

Test yourself

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

Which receptor actions of epinephrine reverse the main features of anaphylaxis?

Alpha-1 vasoconstriction (hypotension, oedema), beta-1 cardiac stimulation and beta-2 bronchodilation with less mast-cell mediator release.

Where is epinephrine injected in anaphylaxis, and where is it avoided?

Into the anterolateral thigh muscle. The buttock, fingers, hands and feet are avoided because of poor absorption, infection or ischaemic necrosis.

What can happen to the pressure of a patient on a non-selective beta blocker who receives epinephrine?

With beta-2 vasodilation blocked, the alpha-1 vasoconstriction acts unopposed and blood pressure can rise sharply; arrhythmias are also more likely.

Which metabolic changes does an epinephrine infusion cause?

Hyperglycaemia (glycogenolysis, less insulin release) and a rise in blood lactate.

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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 - EPINEPHRINE injection (DailyMed (U.S. National Library of Medicine), 2026); Epinephrine Injection: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); eEML - Electronic Essential Medicines List (World Health Organization, 2025).

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Representative model, for educational purposes only.