DurgicalDurgical
EN
Open the app

Pharmacology · Vasopressors and inotropes

Isoprenaline !

A pure beta agonist given intravenously. It speeds and strengthens the heart and relaxes the bronchi; it can bridge bradycardia or heart block until pacing.

Updated 2026-11-01

Also called: Isoproterenol

The figure shows isoprenaline bound to the human beta-1 adrenergic receptor in complex with a Gs protein (cryo-EM).

Target in 3D: Beta-1 and beta-2 adrenergic receptors. PDB structure 8S2T (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

Isoprenaline is a potent non-selective beta agonist with very low affinity for alpha receptors. Beta-1 stimulation raises heart rate, conduction and contractility; beta-2 stimulation relaxes bronchial and vascular smooth muscle, lowering peripheral resistance and diastolic pressure.

  1. Isoprenaline stimulates beta-1 and beta-2 receptors
  2. Beta-1: faster rate, faster conduction, stronger contraction
  3. Beta-2: bronchodilation and vasodilation; diastolic pressure falls

Pharmacokinetics

Metabolism
Mainly by COMT in the liver and other tissues
Half-life
Short; the effect fades soon after the infusion stops

Indications

  • Distributive shock or shock from low cardiac output, to improve haemodynamics
  • Bronchospasm during anaesthesia
  • Emergency treatment of bradycardia or heart block until pacing is available Atrioventricular (heart) block →

Adverse effects

Common

  • Tachycardia and palpitations
  • Nervousness, headache and dizziness
  • Flushing, sweating, tremor and nausea
  • Dyspnoea

Contraindications

  • Tachycardia
  • Ventricular arrhythmias
  • Angina pectoris

Key interactions

Epinephrine
Both stimulate the heart: serious arrhythmias; not given at the same time
Tricyclic antidepressants, MAO inhibitors, levothyroxine and some antihistamines
Stronger response to isoprenaline
Beta blockers such as propranolol
Cardiac and bronchodilating effects are antagonised

What is monitored

  • Continuous ECG and heart rate
  • Blood pressure
  • Chest pain and signs of ischaemia

Administration and safety

  • Intravenous infusion by pump after dilution; use the diluted solution promptly.
  • Do not use the solution if it is pinkish, darker than slightly yellow or contains a precipitate.
  • Do not run it at the same time as epinephrine.
  • Start at the lowest rate and increase gradually according to response.

Nursing care

  • Continuous ECG: report a heart rate above the set target, new arrhythmias or chest pain.
  • Check blood pressure often; diastolic pressure tends to fall.
  • In heart block, the pacing team is alerted early; isoprenaline is a bridge.

Pregnancy and breastfeeding

Human data are limited; it is used when the maternal condition requires it.

Test yourself

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

Why does isoprenaline lower diastolic pressure while raising heart rate?

It stimulates beta-2 receptors that dilate vessels (especially in skeletal muscle) and has almost no alpha effect, while beta-1 speeds the heart.

Which three conditions contraindicate isoprenaline?

Tachycardia, ventricular arrhythmias and angina pectoris.

Why must isoprenaline and epinephrine not be given together?

Both are direct cardiac stimulants, and their combined effect can cause serious arrhythmias.

Add to my cards (3)

← Back to the class: 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 - ISOPROTERENOL HYDROCHLORIDE injection, solution (DailyMed (U.S. National Library of Medicine), 2022); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 14 (McGraw Hill, 2023).

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.