Isoproterenol (Isoprenaline): Indications and Dosing
Primary Indications
Isoproterenol is indicated for improving hemodynamic status in distributive shock and shock due to reduced cardiac output, and for treating bronchospasm occurring during anesthesia. 1
Shock and Hemodynamic Support
- For adult patients in shock, initiate isoproterenol as an intravenous infusion at 0.5 to 5 mcg per minute, titrating based on heart rate, central venous pressure, systemic blood pressure, and urine flow. 1
- Dilute 5 mL (1 mg) in 500 mL of 5% Dextrose Injection for standard infusion (0.25 mL to 2.5 mL of diluted solution per minute). 1
- Rates over 30 mcg per minute have been used in advanced stages of shock, though this increases risk of adverse effects. 1
- If heart rate exceeds 110 beats per minute, decrease or temporarily discontinue the infusion. 1
Pediatric Dosing for Shock
- The American Heart Association recommends an initial infusion rate of 0.1 mcg/kg/min in children, with the usual range being 0.1 to 1 mcg/kg/min. 1
Bronchospasm During Anesthesia
- For adults with bronchospasm during anesthesia, administer 10 to 20 mcg as a bolus intravenous injection (0.5 to 1 mL of diluted solution). 1
- Dilute 1 mL (0.2 mg) to 10 mL with Sodium Chloride Injection or 5% Dextrose Injection. 1
- The initial dose may be repeated when necessary. 1
Role in Bradycardia Management
Isoproterenol has only a second-line role in treatment of bradycardia and is predominantly used in the electrophysiology laboratory at 1-20 mcg/min intravenously. 2
When to Consider Isoproterenol for Bradycardia
- In patients with sinus node dysfunction or symptomatic bradycardia who are at low likelihood of coronary ischemia, isoproterenol may be considered to increase heart rate (Class IIb recommendation). 2
- Dosing for bradycardia: 20-60 mcg IV bolus followed by doses of 10-20 mcg, or infusion of 1-20 mcg/min based on heart rate response. 2
Critical Limitation for Bradycardia Use
Because isoproterenol increases myocardial oxygen demand through beta-1 effects while decreasing coronary perfusion through beta-2 effects, it is best avoided in settings where there is concern for coronary ischemia. 2
- Two randomized controlled trials of isoproterenol as adjunctive therapy in cardiac arrest did not show improved return of spontaneous circulation or survival to hospital discharge. 2
Absolute Contraindications
Isoproterenol is contraindicated in patients with: 1
- Tachycardia
- Ventricular arrhythmias
- Angina pectoris
Critical Warnings and Precautions
Cardiac Risks
- Isoproterenol may induce cardiac arrhythmias and myocardial ischemia, especially in patients with coronary artery disease or cardiomyopathy. 1
- The drug is a nonselective beta agonist with both chronotropic and inotropic effects, enhancing sinus and atrioventricular nodal function without exerting a vasopressor effect. 2
Sulfite Sensitivity
- Isoproterenol contains sodium metabisulfite, which may cause mild to severe allergic reactions including anaphylaxis or asthmatic episodes, particularly in patients with a history of allergies. 1
- However, the presence of metabisulfite should not preclude its use in emergency situations, even if the patient is sulfite-sensitive, as alternatives may not be satisfactory. 1
Hemodynamic Effects
- Isoproterenol causes peripheral vasodilation through beta-2 receptor stimulation, which can lead to significant hypotension. 3, 4
- In hypoxic conditions, isoproterenol can be cardiotoxic and cause cardiac asystole rather than the typical tachycardia response. 5
Administration Guidelines
- Inspect visually for particulate matter and discoloration prior to administration; do not use if the injection is pinkish or darker than slightly yellow or contains a precipitate. 1
- Diluted solution should be used immediately and unused material should be discarded. 1
- Concentrations up to 10 times greater than standard dilution have been used when limitation of volume is essential. 1
Common Adverse Reactions
The most common adverse reactions include tachycardia and palpitations. 1