A 30-year-old woman with moderate persistent asthma presents with a regular narrow-complex tachycardia at 180 bpm and mild hypotension. Vagal maneuvers fail. Which intravenous agent should be avoided as the next step?
- A Adenosine
- B Diltiazem
- C Both adenosine and metoprolol should be avoided ✓
- D Metoprolol
Correct answer: C. Both adenosine and metoprolol should be avoided
Explanation
In an asthmatic, both adenosine and beta blockers can precipitate severe bronchospasm: adenosine directly triggers bronchoconstriction via mast cell mediator release, and beta blockade antagonizes bronchodilating beta-2 receptors. Diltiazem, a nondihydropyridine calcium channel blocker, slows AV nodal conduction without airway effects and is the appropriate choice here. Note that adenosine remains first-line for stable SVT in patients without reactive airway disease, per Indian exam convention as well.
Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.
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