A short-acting acetylcholinesterase inhibitor is administered intravenously to a suspected case of myasthenia gravis as a bedside diagnostic test. Improvement in muscle strength within seconds confirms the diagnosis. Which drug was used?

• A Pyridostigmine
• B Rivastigmine
• C Physostigmine
• D Edrophonium ✓

Explanation

Edrophonium has the shortest duration of action among cholinesterase inhibitors because it binds reversibly and non-covalently to the active site of acetylcholinesterase, clearing within about 5 to 10 minutes. This brevity makes it ideal for the tensilon test. Pyridostigmine and rivastigmine act for hours and are therapeutic agents, while physostigmine is reserved for anticholinergic toxicity. The distractor that tempts most students is pyridostigmine, but its long duration would produce prolonged cholinergic effects unsuitable for a diagnostic challenge.

Reference: Katzung's Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.