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  1. Pharmacology. Isoproterenol is a catecholamine-like drug that stimulates beta-adrenergic receptors (beta1 and beta2). Its pharmacologic properties include positive inotropic and chronotropic cardiac effects, peripheral vasodilation, and bronchodilation. Isoproterenol is not absorbed orally and shows variable and erratic absorption from sublingual and rectal sites. The effects of the drug are terminated rapidly by tissue uptake and metabolism; effects persist only a few minutes after intravenous injection.

  2. Indications

    1. Severe bradycardia or conduction block resulting in hemodynamically significant hypotension (Bradycardia and atrioventricular (AV) block). Note: After beta-blocker overdose, even exceedingly high doses of isoproterenol may not overcome the pharmacologic blockade of beta-receptors, and glucagon is the preferred agent.

    2. To increase heart rate and thereby abolish polymorphous ventricular tachycardia (torsade de pointes) associated with QT-interval prolongation (Table I–7).

    3. To relieve bronchospasm (although beta2-selective drugs such as albuterol are preferred).

  3. Contraindications

    1. Do not use isoproterenol for ventricular fibrillation or ventricular tachycardia (other than torsade de pointes).

    2. Use with extreme caution in the presence of halogenated or aromatic hydrocarbon solvents or anesthetics or chloral hydrate.

  4. Adverse effects

    1. Increased myocardial oxygen demand may result in angina pectoris or acute myocardial infarction.

    2. Peripheral beta2-adrenergic-mediated vasodilation may worsen hypotension.

    3. The drug may precipitate ventricular arrhythmias.

    4. Sulfite preservative in some parenteral preparations may cause hypersensitivity reactions.

    5. Hypokalemia may occur secondary to beta2-adrenergic-mediated intracellular potassium shift.

    6. Use in pregnancy. FDA Category C (indeterminate). This does not preclude its acute, short-term use for a seriously symptomatic patient (Introduction). However, it may cause fetal ischemia and also can reduce or stop uterine contractions.

  5. Drug or laboratory interactions

    1. Additive beta-adrenergic stimulation occurs in the presence of other sympathomimetic drugs, theophylline, and glucagon.

    2. Administration in the presence of cyclopropane, halogenated anesthetics, or other halogenated or aromatic hydrocarbons may enhance the risk for ventricular arrhythmias because of sensitization of the myocardium to the arrhythmogenic effects of catecholamines.

    3. Digitalis-intoxicated patients are more prone to develop ventricular arrhythmias when isoproterenol is administered.

    4. Beta-blockers may interfere with the action of isoproterenol by competitive blockade at beta-adrenergic receptors.

  6. Dosage and method of administration

    1. For intravenous infusion, use a solution containing 4 mcg/mL (dilute 5 mL of 1:5,000 solution in 250 mL of D5W,); begin with an infusion at 0.5–1 mcg/min (children: 0.1 mcg/kg/min) and increase as needed for desired effect or as tolerated (determined by monitoring for arrhythmias). Usual dosage range is 2–10 mcg/min. For emergency treatment, the infusion rate may start at 5 mcg/min. The usual upper dose is 20 mcg/min (1.5 mcg/kg/min in children), but as much as 200 mcg/min has been given in adults with propranolol overdose. Preparations will degrade (and turn dark) with exposure to light, air, or heat.

    2. For IV bolus, the usual adult dose is 20–60 mcg (1-3 mL of a 1:50,000 solution) and repeat bolus doses of 10–200 mcg. Make a solution of 1:50,000 (20 mcg/mL) by diluting 1 mL of the 1:5,000 solution to a volume ...

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