What is the recommended dose and administration of adrenaline (epinephrine) in asthma, particularly when used with dilution?

Epinephrine Dosage and Administration in Asthma

For severe asthma exacerbations, epinephrine should be administered subcutaneously at 0.01 mg/kg of 1:1000 solution (maximum: 0.3–0.5 mg) and may be repeated every 20 minutes for up to 3 doses, while simultaneously initiating treatment with inhaled beta-agonists and corticosteroids. 1

Dosing Guidelines for Epinephrine in Asthma

Subcutaneous Administration

• Dose: 0.01 mg/kg of 1:1000 solution
• Maximum dose: 0.3–0.5 mg
• Frequency: May repeat every 20 minutes up to 3 doses
• Important: Begin simultaneous treatment with inhaled beta-agonists (albuterol) and corticosteroids 1

Nebulized Administration Options

• For laryngotracheobronchitis (croup) with airway edema:
  • 0.5 mL/kg of 1:1000 solution (maximum: 5 mL = 5 mg) administered by nebulizer 1
  • Alternative: 2.25% inhalation solution: 0.05 mL/kg (maximum: 0.5 mL) in 2 mL of normal saline 1

Clinical Considerations

Efficacy Comparison

Studies comparing nebulized epinephrine (adrenaline) with salbutamol have shown similar efficacy in acute asthma. A controlled trial found that nebulized adrenaline (2 mg) was as effective as salbutamol (5 mg) in acute severe asthma, with both drugs inducing significant improvements in peak expiratory flow and decreases in heart rate and respiratory frequency 2.

Route of Administration Considerations

• The subcutaneous route is recommended for asthma specifically 1
• For patients with mild to moderate asthma, aerosol epinephrine may produce fewer side effects than injected epinephrine while maintaining similar efficacy 3
• For severe airway obstruction (PEFR <120 or <25% of predicted normal), parenteral epinephrine has been shown to be superior to aerosol administration 3

Important Safety Precautions

• Always ensure selection of the appropriate concentration for the route of administration and patient age/condition
• Conversion guide: 0.01 mg/kg = 0.1 mL/kg of 1:10,000 solution and 0.1 mg/kg = 0.1 mL/kg of 1:1000 solution 1
• Monitor for potential side effects including tachyarrhythmias, ectopic beats, and blood pressure changes

Special Considerations

Severe Cases

• In cases of severe acute asthma not responding to initial therapy, intravenous epinephrine may be considered at a dose of 0.33 μg/kg/minute, in association with intravenous steroid therapy and aminophylline 4
• This approach has shown good clinical improvement with low rates of requiring mechanical ventilation (2.3% overall) 4

Comparison with Selective Beta-2 Agonists

Recent systematic review evidence suggests that epinephrine and selective β2-agonists have similar efficacy in acute asthma, though the overall quality of evidence is low 1. The non-selective properties of epinephrine (alpha and beta effects) may provide additional benefits through:

• Reduction in microvascular leakage and edema via alpha-receptor stimulation
• Inhibition of bronchoconstrictor neural pathways 5

Remember that while epinephrine is valuable in severe asthma, it should be administered as part of a comprehensive treatment approach that includes inhaled beta-agonists and systemic corticosteroids.