isoprenaline

Isoprenaline (isoproterenol) is a synthetic, non-selective beta-adrenergic agonist used in cardiac and respiratory medicine. It stimulates beta-1 and beta-2 receptors, producing positive chronotropic and inotropic effects and bronchodilation. These actions increase heart rate and contractility and improve AV nodal conduction, while beta-2 stimulation causes relaxation of bronchial smooth muscle and vasodilation in skeletal muscle beds.

Isoprenaline is used in acute care settings to treat severe bradycardia and heart block when pacing is not available. It may be used as an inotrope in cardiogenic shock or during certain electrophysiology procedures to evaluate AV conduction. Its use for asthma or bronchospasm is historical; it has largely been replaced by beta-2 selective agonists.

The combined beta-1 and beta-2 effects raise heart rate, stroke volume, and AV conduction; bronchodilation reduces airway resistance. Vasodilatory effects on skeletal muscle can lower diastolic pressure; tachycardia can increase myocardial oxygen demand.

Pharmacokinetics and administration: Isoprenaline is usually given by intravenous infusion for rapid onset and short duration; it is not active orally and is rapidly inactivated by catechol-O-methyltransferase and monoamine oxidase in the gut and liver.

Safety and side effects: Common adverse effects include tachycardia, palpitations, tremor, headache, and arrhythmias; it can cause angina or myocardial ischemia in patients with coronary disease and may cause hypotension due to vasodilation in some vascular beds. It should be used with caution in patients with tachyarrhythmias, severe aortic stenosis, or uncontrolled hypertension.