A neurologist suspects myasthenia gravis in a 30-year-old woman with fluctuating ptosis. She administers a short-acting drug intravenously and observes improvement in ptosis within one minute. Which drug was used and why is it suitable diagnostically?
- A Pyridostigmine, because its intermediate duration allows serial testing
- B Edrophonium, because its very brief action of 5 to 10 minutes permits rapid assessment with minimal risk of cholinergic crisis ✓
- C Rivastigmine, because it crosses the blood-brain barrier to enhance central cholinergic tone
- D Ambenonium, because its irreversible binding gives a definitive response
Correct answer: B. Edrophonium, because its very brief action of 5 to 10 minutes permits rapid assessment with minimal risk of cholinergic crisis
Explanation
Edrophonium is a short-acting, reversible acetylcholinesterase inhibitor whose onset within seconds and duration of only 5 to 10 minutes make it ideal for the tensilon test: transient improvement in strength supports myasthenia gravis. Pyridostigmine lasts several hours and is used for chronic therapy, not diagnosis. Rivastigmine is a centrally acting agent for dementia, and ambenonium is a longer-acting reversible inhibitor used in maintenance therapy, neither suitable for bedside diagnostic use.
Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.
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