Is epinephrine (adrenaline) effective for treating acute asthma?

Epinephrine for Acute Asthma: Evidence-Based Recommendations

Epinephrine should NOT be used routinely in acute asthma exacerbations, as it offers no advantage over selective β2-agonists (like albuterol) and has a worse cardiovascular side effect profile, but it is indicated specifically when concomitant anaphylaxis/angioedema is present or in life-threatening asthma unresponsive to first-line therapies. 1

When Epinephrine IS Indicated

Epinephrine has three specific clinical scenarios where use is appropriate:

• Anaphylaxis with asthma: When concomitant anaphylaxis or angioedema is present, epinephrine becomes the primary treatment (not just for asthma, but for the anaphylaxis itself). 1

• Life-threatening asthma unresponsive to standard therapy: Consider epinephrine only after repeated courses of inhaled β2-agonists have failed in severe or life-threatening presentations. 1

• Inability to cooperate with inhaled therapy: In prehospital settings or when patients cannot use inhalers effectively, epinephrine may be considered as an alternative route of bronchodilator delivery. 1

Why Epinephrine Is NOT First-Line

The evidence clearly demonstrates epinephrine's limitations:

• Equivalent efficacy to selective β2-agonists: Meta-analysis shows a pooled odds ratio for treatment failure of 0.99 (95% CI 0.75-1.32), meaning no clinically meaningful difference in effectiveness between epinephrine and albuterol. 1, 2

• Worse side effect profile: Epinephrine's non-selective adrenergic properties cause increased heart rate, myocardial irritability, and increased myocardial oxygen demand—effects that selective β2-agonists avoid. 1, 3

• Cardiovascular risks: IV epinephrine carries a 4% risk of serious side effects, and adverse events occurred in 30.5% of cases in one series (though most were minor). 2, 4

• Very low quality evidence: Current recommendations against routine use are based on very low-quality evidence with serious risk of bias, significant inconsistency between studies, and imprecision in effect estimates. 1

Proper Administration When Indicated

If epinephrine is warranted, use these evidence-based protocols:

Subcutaneous route (preferred for most cases):

• Dose: 0.01 mg/kg (approximately 0.3 mg) using 1:1000 concentration 1, 2
• Can repeat every 20 minutes for up to 3 doses 1, 2
• Better tolerated than previously thought, even in patients over 35 years 1

Intramuscular route (alternative in prehospital settings):

• Provides rapid absorption and effect for severe or life-threatening asthma 1
• Same dosing as subcutaneous route 1

Intravenous route (only for truly life-threatening cases):

• Continuous infusion at 0.25-1 mcg/min 1
• Carries 4% risk of serious side effects 1
• No proven improved outcomes compared to inhaled selective β2-agonists 2
• Should be reserved for extreme circumstances only 5

Critical Pitfalls to Avoid

• Do NOT delay first-line therapies: Never delay oxygen, nebulized β2-agonists, and systemic corticosteroids while considering epinephrine. 1

• Do NOT use as first-line when inhalers are available: Modern guidelines prioritize high-dose inhaled β2-agonists, early systemic corticosteroids, and ipratropium bromide for severe exacerbations. 2

• Beware of cardiac asthma mimicking status asthmaticus: Epinephrine can precipitate cardiogenic shock in patients with unrecognized left ventricular dysfunction, as its vasoconstrictive properties worsen hemodynamic status. 6

• Avoid in patients with cardiac risk factors unless absolutely necessary: While better tolerated than historically believed, cardiovascular risks remain, particularly with IV administration. 2

The Standard Treatment Algorithm

First-line for ALL acute asthma exacerbations:

• Oxygen to maintain SaO2 >90% (>95% in pregnant women and patients with heart disease) 1
• High-dose inhaled short-acting β2-agonists (albuterol/salbutamol) 1, 2
• Systemic corticosteroids 1, 2

For severe exacerbations, ADD:

• Ipratropium bromide 1
• Consider magnesium sulfate 7

Only THEN consider epinephrine if:

• Anaphylaxis/angioedema is present, OR 1
• Patient remains unresponsive to repeated courses of inhaled therapy, OR 1
• Patient cannot cooperate with inhaled therapy 1

Important Context: Historical vs. Current Practice

Epinephrine was historically the mainstay of acute asthma treatment before selective β2-agonists became available, but international asthma guidelines no longer recommend it except with concomitant anaphylaxis. 2 This creates a discrepancy where many prehospital ambulance guidelines still commonly recommend epinephrine for severe asthma, conflicting with current evidence-based international asthma guidelines. 1 In hospital settings, prioritize selective β2-agonists over epinephrine unless specific indications are met.