What is the recommended dose of isoprenaline for bradycardia and asthma?

Isoprenaline Dosing for Bradycardia and Asthma

For bradycardia, isoprenaline should be administered at 1-20 mcg/min intravenously, while for bronchospasm, the recommended dose is 10-20 mcg as an intravenous bolus injection. 1

Isoprenaline for Bradycardia

Dosage and Administration

• For symptomatic bradycardia, isoprenaline is administered as an intravenous infusion at 1-20 mcg/min based on heart rate response 2
• Preparation typically involves diluting 5 mL (1 mg) in 500 mL of 5% Dextrose Injection 1
• Initial infusion should start at the lowest recommended dose (0.5-5 mcg/min) and be increased gradually based on patient response 1
• Adjust infusion rate based on heart rate, central venous pressure, systemic blood pressure, and urine flow 1
• Consider decreasing or temporarily discontinuing the infusion if heart rate exceeds 110 beats per minute 1

Clinical Considerations for Bradycardia

• Isoprenaline is generally considered a second-line agent for bradycardia after atropine (0.5-1 mg IV, maximum 3 mg) has failed 2, 3
• It is predominantly used in the electrophysiology laboratory and has only a second-line role in treatment of bradycardia in the setting of resuscitation 2
• In patients with sinus node dysfunction (SND), isoprenaline may be considered when symptoms or hemodynamic compromise are present and the patient is at low likelihood of coronary ischemia 2
• Isoprenaline should be avoided in settings where there is concern for coronary ischemia as it increases myocardial oxygen demand while potentially decreasing coronary perfusion 2

Special Populations

• For pediatric patients, the American Heart Association recommends an initial infusion rate of 0.1 mcg/kg/min, with the usual range being 0.1-1 mcg/kg/min 1
• In post-heart transplant patients, isoprenaline may be used, but atropine should be avoided as it can cause paradoxical heart block 3

Isoprenaline for Asthma/Bronchospasm

Dosage and Administration

• For bronchospasm occurring during anesthesia, administer 10-20 mcg (0.5-1 mL of diluted solution) as an intravenous bolus injection 1
• Preparation involves diluting 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

Clinical Considerations for Asthma

• Isoprenaline has been largely replaced by more selective beta-2 agonists (like salbutamol) for asthma treatment due to its significant cardiac effects 4
• Studies show isoprenaline causes greater increases in heart rate and greater changes in blood pressure compared to the same dose of salbutamol 4
• The effect of isoprenaline on heart rate is about 10 times greater than salbutamol, though the bronchodilator effects are equipotent 4

Precautions and Monitoring

• Carefully monitor heart rate, blood pressure, and ECG during administration 2, 1
• Isoprenaline can increase myocardial oxygen demand through beta-1 effects while decreasing coronary perfusion due to beta-2 effects 2
• Use with extreme caution in hypoxic conditions as animal studies have shown increased cardiotoxicity of isoprenaline during hypoxia 5
• Paradoxical bradycardia has been reported in approximately 7% of patients receiving isoprenaline infusion, particularly in those with hypervagotonia 6
• Higher doses (>20 mcg/min) may result in vasoconstriction or arrhythmias 2
• Isoprenaline affects multiple metabolic pathways including increasing plasma free fatty acids, insulin levels, and plasma renin activity 7

Alternative Treatments

• For bradycardia: atropine (first-line), epinephrine (2-10 mcg/min), or dopamine (5-20 mcg/kg/min) 2, 3
• For bradycardia refractory to medication: transcutaneous or transvenous pacing 2
• For asthma: selective beta-2 agonists like salbutamol are preferred due to fewer cardiac side effects 4