Why is adenosine contraindicated in asthma?

Adenosine Contraindication in Asthma

Adenosine is contraindicated in asthma because it can cause significant bronchoconstriction in asthmatic patients, potentially leading to severe respiratory difficulties and life-threatening bronchospasm. 1

Mechanism of Adenosine-Induced Bronchoconstriction

• Adenosine causes bronchoconstriction specifically in asthmatic patients but not in normal subjects with healthy airways 2
• The bronchoconstriction occurs primarily through indirect mechanisms:
  • Adenosine stimulates mast cells (particularly through A2B receptors), causing release of inflammatory mediators that trigger bronchial smooth muscle contraction 2
  • This effect is more pronounced in atopic and asthmatic individuals compared to non-atopic controls 2
• Adenosine can augment mediator release from mast cells that are already primed for release, which is common in asthmatic airways 2, 3

Clinical Evidence Supporting the Contraindication

• The FDA drug label explicitly lists "known or suspected bronchoconstrictive or bronchospastic lung disease (e.g., asthma)" as an absolute contraindication for adenosine administration 1
• Adenosine administration can cause dyspnea, bronchoconstriction, and respiratory compromise in susceptible individuals 1
• Even in patients without asthma but with obstructive lung disease, adenosine should be used with extreme caution 1

Comparative Potency and Specificity

• Inhaled adenosine is less potent than histamine in producing bronchoconstriction in asthmatic patients, but still causes significant airway narrowing 4
• Adenosine challenge tests are actually used diagnostically because they show higher specificity for asthma compared to methacholine challenges 2
• Adenosine and adenosine 5'-monophosphate (AMP) challenges can help differentiate asthma from other respiratory conditions like COPD, cystic fibrosis, and bronchiectasis 2

Physiological Response and Safety Concerns

• When administered intravenously (as commonly used in cardiac testing), adenosine can cause:
  • Severe bronchospasm in asthmatic patients 1
  • Respiratory difficulties requiring immediate resuscitative measures 1
• The risk is significant enough that resuscitative equipment should be immediately available when adenosine is administered to any patient 1

Potential Mechanisms of Protection

• Theophylline (a methylxanthine) can antagonize adenosine-induced bronchoconstriction, suggesting competitive receptor antagonism may be involved 4
• Cromolyn sodium has shown protection against adenosine-induced bronchoconstriction in some asthmatic subjects, suggesting mast cell stabilization may help prevent this reaction 5
• However, these protective effects are not reliable enough to overcome the contraindication 1

Clinical Implications

• Healthcare providers must thoroughly screen patients for asthma or bronchospastic disease before administering adenosine 1
• For cardiac testing that would normally use adenosine, alternative pharmacological agents should be considered for patients with asthma 2
• If bronchospasm occurs during adenosine administration, the drug should be immediately discontinued and appropriate resuscitative measures initiated 1