Pharmacology · Cholinesterase inhibitors
Edrophonium !
A very short-acting cholinesterase inhibitor once used as a bedside test for myasthenia gravis. Antibody tests have largely replaced it.
Updated 2026-11-01
The figure shows edrophonium in the active site of Torpedo (electric ray) acetylcholinesterase, an enzyme with the same gorge and catalytic serine as the human one.
Mechanism of action
Edrophonium binds the choline site of acetylcholinesterase reversibly, without forming a covalent bond, and blocks acetylcholine from entering. Its effect lasts only minutes because it is quickly removed by the kidney. In myasthenia gravis, an injection briefly improves strength, which was the basis of the old «edrophonium test».
- Binds the choline site of acetylcholinesterase reversibly
- Acetylcholine is broken down more slowly
- Strength improves briefly in myasthenia gravis
- The kidney clears it quickly
Pharmacokinetics
- Distribution
- Quaternary: acts only in the peripheral nervous system
- Elimination
- Rapid renal elimination, hence its short action
- Onset and duration
- Rapid after intravenous injection; lasts only minutes
Indications
- Diagnostic test for myasthenia gravis (historical; antibody tests are now preferred) Myasthenia gravis →
- Reversal of non-depolarizing neuromuscular block, like neostigmine
Adverse effects
Common
- Salivation, sweating and tearing
- Nausea and abdominal cramps
- Fasciculations
Contraindications
- Mechanical obstruction of the bowel or urinary tract (class)
- Caution in asthma and heart rhythm disorders (class)
Key interactions
- Atropine
- Kept ready to treat bradycardia during the test
- Succinylcholine
- Prolonged block (class effect)
What is monitored
- Heart rate and ECG during the test
- Strength of a defined muscle (for example eyelid drooping) before and after
Administration and safety
- Given intravenously in a monitored setting with atropine and airway equipment at hand
Nursing care
- Attach a cardiac monitor before the injection
- Watch for slow heart rate and wheeze
- Record the muscle response the team is testing
Test yourself
Think of the answer, then tap the question to see it.
Why does edrophonium act for only a few minutes?
It binds acetylcholinesterase reversibly without a covalent bond and is quickly eliminated by the kidney.
What was a positive edrophonium test in myasthenia gravis?
A brief, clear improvement in muscle strength after the injection.
What has largely replaced the edrophonium test?
Blood tests for antibodies against the acetylcholine receptor, plus electrodiagnostic studies.
Related drugs
Related conditions
← Back to the class: Cholinesterase inhibitors
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 12 (McGraw Hill, 2023); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); RCSB PDB - 1AX9: ACETYLCHOLINESTERASE COMPLEXED WITH EDROPHONIUM, LAUE DATA (RCSB Protein Data Bank, 2026).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.