A myasthenia gravis patient on pyridostigmine presents with worsening weakness and respiratory difficulty. Which drug is used at the bedside to differentiate a myasthenic crisis from a cholinergic crisis?
- A Neostigmine
- B Edrophonium ✓
- C Atropine
- D Pralidoxime
Correct answer: B. Edrophonium
Explanation
Edrophonium is a very short-acting acetylcholinesterase inhibitor (action lasting about 5 minutes). In a myasthenic crisis, weakness briefly improves after injection; in a cholinergic crisis, muscarinic side effects worsen and weakness does not improve. Its ultra-short duration is precisely what makes it suitable as a diagnostic test, whereas longer-acting agents such as neostigmine or pyridostigmine would produce sustained cholinergic toxicity if the crisis were cholinergic.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
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