DESCRIPTION

Edrophonium is a medication used in the diagnosis of myasthenia gravis and occasionally in the treatment of snakebite.

FORMS AND USES

Edrophonium chloride (Tensilon, Enlon, Reversol)

MECHANISM OF ACTION

• Edrophonium is a reversible inhibitor of the enzyme acetylcholinesterase in the synaptic junction.
• Inhibition of acetylcholinesterase in the synaptic junction increases the concentration of acetylcholine, thereby overcoming the effect of blockade of the acetylcholine receptor.
• The onset of action is 30 to 60 seconds, and its duration is 10 to 30 minutes.

DRUG AND DISEASE INTERACTIONS

• Synergistic cholinergic effects can occur in patients with pre-existing cholinergic inhibition (neostigmine, pyridostigmine, physostigmine, organophosphate, or carbamate insecticides).
• Increased dysrhythmias may occur with digoxin, calcium channel blockers, or beta-blockers.
• Quinidine may antagonize the effects of edrophonium and may mask diagnostic response in patients with myasthenia gravis.
• Procainamide may antagonize the effects on skeletal muscle.

PREGNANCY AND LACTATION

US FDA Pregnancy Category C. Studies have shown that the drug exerts teratogenic or embryocidal effects, but there are no controlled studies in women, or no studies are available in either animals or women.

Section Outline:

• DESCRIPTION
• FORMS AND USES
• MECHANISM OF ACTION
• DRUG AND DISEASE INTERACTIONS
• PREGNANCY AND LACTATION

• Edrophonium acts as an antagonist to nondepolarizing, neuromuscular blockers:
  • It is used for postoperative, postprocedure reversal of paralysis.
  • It is used for bites of the Philippine cobra (Naja naja phillippinesis), as well as some other snakebites with neurotoxicity, especially if antivenom is unavailable.

CONTRAINDICATIONS

• Known hypersensitivity to cholinergic agonists
• Known adequate anticholinesterase therapy
• Organophosphate or carbamate poisoning

ADVERSE EFFECTS

• Acute overdose or oversensitivity reactions are usually manifested by symptoms of muscarinic cholinergic receptor stimulation: nausea, vomiting, diarrhea, sweating, increased bronchial and salivary secretions, bradycardia, and hypotension.
• Bradycardia and cardiac standstill may occur.
• Respiratory weakness may occur.
• Airway obstruction by secretions may occur.

Section Outline:

• CONTRAINDICATIONS
• ADVERSE EFFECTS

• As an antagonist to nondepolarizing, neuromuscular blockers. The dose for adults is 10 mg given intravenously over 30 to 45 seconds, repeated as necessary to a maximum of 40 mg. The pediatric dose is 233 µg/kg.
• Bite by Philippine cobra, or some other snakebites with neurotoxicity if antivenom is unavailable
  • Atropine is administered intravenously (0.6 mg for adults, 50 µg/kg for children).
  • Then edrophonium is administered.
    • The adult test dose is 2 mg given intravenously over 15 to 30 seconds. If there is no reaction in 45 seconds, another 8 mg (total 10 mg) is injected.
    • For children over 75 pounds, the test dose is 1 mg given intravenously over 15 to 30 seconds. If there is no reaction in 45 seconds, the remainder of up to 5 mg is injected.
    • For children under 75 pounds, the dose is 2 mg given intramuscularly.
    • The effect of each dose should be carefully assessed before giving additional edrophonium.

• Cholinergic symptoms of excessive respiratory secretions and bradycardia from edrophonium are common.
• Symptoms of cholinergic excess in patients already on anticholinesterases may complicate therapy.
• Hypoxia may result if inadequate airway management is provided when cholinergic effects occur.
• Neurotoxicity from snakebite may produce respiratory paralysis indistinguishable from that seen as an adverse reaction to edrophonium.
• Hypotension may occur and should be managed with isotonic fluid infusion, Trendelenburg position, and, if needed, dopamine.
• Seizures may occur and should be controlled with benzodiazepine administration; phenytoin and phenobarbital are second-line treatments.
• Cardiac rhythm should be monitored continuously until the dysrhythmia resolves, the airway is controlled, and the patient is stable.
• Geriatric patients have an increased susceptibility to dysrhythmia and greater likelihood of underlying renal failure and drug-drug interactions.

Poisoning by drugs primarily affecting the autonomic nervous system: parasympathetics (cholinergics).

See Also: SECTION II, Hypotension, Seizure, and Bradycardia chapters; SECTION III, Atropine chapter; and SECTION IV, Edrophonium chapter.

RECOMMENDED READING

Gilman AG, Rall TW, Nies AS, et al., eds. Goodman and Gilman's the pharmacological basis of therapeutics, 8th ed. New York: Pergamon, 1990.

Osserman KE, Kaplan LI. Rapid diagnostic test for myasthenia gravis: increased muscle strength, without fasciculations, after intravenous administration of edrophonium (TensilonR chloride). JAMA 1952;150:265-268.

Youngberg JA. Cardiac arrest following treatment of paroxysmal atrial tachycardia with edrophonium. Anesthesiology 1979;50:234-235.

Author: Steven A. Seifert

Reviewer: Luke Yip