How to initiate isoprenaline (isoproterenol) therapy?

How to Initiate Isoprenaline (Isoproterenol) Therapy

Start isoprenaline at 0.5 to 5 mcg/min as a continuous intravenous infusion for shock, or 10 to 20 mcg as an intravenous bolus for bronchospasm during anesthesia. 1

Preparation and Administration Route

• Dilute 1 mg of isoprenaline in 100 mL of normal saline or D5W to create a concentration suitable for infusion 2
• Administer via continuous intravenous infusion using an infusion pump for precise dose control 1
• Central venous access is not specifically required for isoprenaline, unlike norepinephrine, though IV access must be secure 1

Initial Dosing by Indication

For Bradycardia in Acute Heart Failure

• Begin with 2 mcg/min and titrate up to a maximum of 20 mcg/min based on heart rate response 2
• Use as an interim measure only when atropine (0.25-0.5 mg IV, up to 1-2 mg total) has failed 2
• Avoid in ischemic conditions as isoprenaline increases myocardial oxygen demand and can worsen ischemia 2
• Prepare for temporary pacemaker insertion if no response is achieved with medical therapy 2

For Distributive Shock or Reduced Cardiac Output

• Start at 0.5 mcg/min and increase gradually to 5 mcg/min as an intravenous infusion 1
• Titrate based on hemodynamic response, targeting improvement in blood pressure and tissue perfusion 1

For Bronchospasm During Anesthesia

• Administer 10 to 20 mcg as an intravenous bolus injection 1
• Repeat as needed based on bronchodilator response 3

For Tilt Table Testing (Diagnostic Use)

• Use an incremental infusion rate from 1 up to 3 mcg/min to increase average heart rate by approximately 20-25% over baseline 2
• Administer without returning the patient to the supine position during the drug challenge phase 2
• Continue for 15-20 minutes during the drug provocation phase 2

Titration Strategy

• Begin at the lowest recommended dose and increase gradually based on patient response 1
• For bradycardia, titrate every few minutes until heart rate improves or maximum dose (20 mcg/min) is reached 2
• For shock, adjust infusion rate in 0.5-1 mcg/min increments based on hemodynamic parameters 1
• Maximal bronchodilator effect occurs within 2-5 minutes of starting or stopping the infusion 3

Monitoring Requirements

• Continuously monitor cardiac rhythm for development of tachycardia or ventricular arrhythmias 1
• Measure blood pressure frequently during initiation and titration 1
• Assess heart rate response—expect increases of 20-25% over baseline at therapeutic doses 2
• Monitor for signs of myocardial ischemia, particularly in patients with coronary artery disease 2

Critical Contraindications

Do not administer isoprenaline in patients with: 1

• Pre-existing tachycardia
• Ventricular arrhythmias
• Angina pectoris or active myocardial ischemia

Important Drug Interactions and Precautions

• Never administer isoprenaline simultaneously with epinephrine as combined effects may induce serious arrhythmias 1
• Beta-adrenergic blocking drugs will reduce the cardiostimulating and bronchodilating effects of isoprenaline 1
• Tricyclic antidepressants, MAO inhibitors, levothyroxine, and certain antihistamines may potentiate the clinical response 1
• Isoprenaline contains metabisulfite, which may cause allergic reactions in susceptible individuals 1

Special Clinical Scenarios

Polymorphic Wide-Complex Tachycardia with Acquired Long QT

• Avoid isoprenaline in familial long QT syndrome as it is contraindicated 2
• Consider isoprenaline when polymorphic tachycardia is accompanied by bradycardia or appears precipitated by pauses in rhythm, specifically in acquired (not familial) long QT 2
• Combine with pacing or IV magnesium as appropriate 2

Asthma with Refractory Bronchial Obstruction

• For severe asthma unresponsive to inhaled therapy, use doses of 0.0375 to 0.225 mcg/kg/min 3
• Ensure adequate oxygenation and continuous cardiac monitoring 3
• Major advantage is administration of bronchodilator to airways not reached by inhalation 3

Common Pitfalls to Avoid

• Do not use in ischemic conditions (particularly AMI with right coronary artery occlusion) as it can worsen myocardial ischemia 2
• Avoid prolonged use—isoprenaline is intended as a temporary bridge to definitive therapy (pacing for bradycardia, intubation for severe asthma) 2, 3
• Do not rely on isoprenaline as sole therapy for bradycardia—always prepare for pacemaker insertion 2
• Paradoxical bradycardia can occur in 7% of patients, particularly those with hypervagotonia, though this is usually without clinical significance 4
• Be aware that vagal activity actually increases during isoprenaline infusion despite the chronotropic effect 5