A 28-year-old woman reports drooping eyelids that worsen through the day. On intravenous injection of a test drug, her ptosis resolves dramatically within 45 seconds but returns after 8 minutes. The drug most likely administered was:
- A Pyridostigmine
- B Physostigmine
- C Edrophonium ✓
- D Pralidoxime
Correct answer: C. Edrophonium
Explanation
Edrophonium is a quaternary ammonium compound that reversibly binds the anionic site of acetylcholinesterase for only a few minutes, making it the classical agent for the Tensilon diagnostic test in myasthenia gravis. Pyridostigmine takes longer to act and lasts hours, so it cannot serve as a rapid diagnostic agent. Physostigmine is tertiary and crosses into the CNS, which is irrelevant here.
Reference: Katzung's Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.