Edrophonium

Summary

Edrophonium is a cholinesterase inhibitor used primarily in the diagnosis of Myasthenia Gravis. It works in the periphery only to inhibit the breakdown of acetylcholine, which outcompete myasthenic antibodies to providing brief symptomatic improvement for the patient. This brief symptomatic improvement with Edrophonium is diagnostic for MG, and another name for this test is the Tensilon Test.

Key Points

• Edrophonium
  • Also known by its trade name, Tensilon
  • Mechanism
    • Cholinesterase inhibitor (anticholinesterase)
      • Prevents acetylcholine (ACh) breakdown, which increases ACh at neuromuscular junction
    • Works peripherally (does not cross BBB)
      • Quaternary amine structure is too polar to cross the blood brain barrier
      • This prevents its use for treatment of atropine poisoning because it cannot reverse CNS effects of atropine (use Physostigmine instead)
  • Indications
    • Diagnosis of myasthenia gravis (Tensilon Test)
      • Effects begin in 30-60 seconds and last ~10 minutes; short duration is optimal for diagnosis but not treatment
      • Purely diagnostic use case is mostly historical, as MG is now diagnosed by anti-acetylcholine receptor Ab (myasthenic antibody)
      • However, edrophonium is currently used to differentiate between 2 cases: (1) undertreated MG with a myasthenic crisis (aka not enough ACh in the cleft), which will improve with edrophonium, (2) overtreatment with AChEIs (cholinergic crisis), which causes too much ACh and refractory muscle, and will not improve with edrophonium
    • Nondepolarizing neuromuscular blocking drugs blockade reversal
      • along with neostigmine and other cholinesterase inhibitors
    • Treatment of ileus (e.g. postoperative)
    • Treatment of arrhythmias
  • Adverse Effects
    • Cholinergic Overstimulation
      • Effects sometimes memorized using the mnemonic DUMBELLS: Diarrhea, Urination, Miosis, Bradycardia, Emesis, Lacrimation, Lethargy, and Salivation
  • Reversal of overdose
    • Atropine or Pralidoxime