edrophonium chloride
Enlon, Reversol, Tensilon

Available forms
Available by prescription only
Injection: 10 mg/ml in 1-ml ampule, 10-ml vial, 15-ml vial

Indications and dosages
 Curare antagonist (to reverse neuromuscular blocking action). Adults: 10 mg I.V. over 30 to 45 seconds, repeated p.r.n. to 40-mg maximum dose. Larger doses may potentiate rather than antagonize effect of curare.
 Diagnostic aid in myasthenia gravis. Adults: 2 mg I.V. within 15 to 30 seconds; then 8 mg if no response (increased muscular strength) occurs. Or, 10 mg I.M. If cholinergic reaction occurs, 2 mg I.M. 30 minutes later to rule out false-negative response.
Children who weigh more than 34 kg (75 lb): 2 mg I.V. If no response within 45 seconds, give 1 mg q 45 seconds to maximum dose of 10 mg. Or, 5 mg I.M.
Children who weigh 34 kg or less: 1 mg I.V. If no response within 45 seconds, give 1 mg q 45 seconds to maximum dose of 5 mg. Or, 2 mg I.M.
Infants: 0.5 mg I.V.
 To differentiate myasthenic crisis from cholinergic crisis. Adults: 1 mg I.V. If no response in 1 minute, repeat dose once. Increased muscle strength confirms myasthenic crisis; no increase or exaggerated weakness confirms cholinergic crisis.
 Tensilon test for evaluating treatment requirements in myasthenia gravis. Adults: 1 to 2 mg I.V. 1 hour after oral intake of drug being used in treatment. Response will be myasthenic in the undertreated patient, adequate in the controlled patient, and cholinergic in the overtreated patient.
 To terminate paroxysmal atrial tachycardia or as an aid in diagnosing supraventricular tachyarrhythmias and evaluating the function of demand pacemakers. ◇ Adults: 10 mg I.V. over 5 minutes.
≡ Dosage adjustment. For elderly or digitalized adults, 5 to 7 mg I.V. over 5 minutes.
 To slow supraventricular tachyarrhythmias unresponsive to a cardiac glycoside. ◇ Adults: 2 mg/minute I.V. test dose, followed by 2 mg q minute until a total dose of 10 mg is given. If heart rate decreases in response to this dose, infusion of 0.25 mg/minute may be started; infusion may be increased to 2 mg/minute, if necessary.

Pharmacodynamics
Cholinergic action: Edrophonium blocks hydrolysis of acetylcholine by cholinesterase, resulting in acetylcholine accumulation at cholinergic synapses. This leads to increased cholinergic receptor stimulation at the neuromuscular junction and vagal sites. Edrophonium is a short-acting drug, which makes it particularly useful for diagnosing myasthenia gravis.

Pharmacokinetics
Absorption: No information available.
Distribution: Not clearly identified.
Metabolism: Exact metabolic fate is unknown; drug isn’t hydrolyzed by cholinesterases.
Excretion: Exact excretion mode is unknown.

Contraindications and precautions
Contraindicated in patients hypersensitive to anticholinesterase drugs and in those with mechanical obstruction of the intestine or urinary tract. Use cautiously in patients with bronchial asthma or arrhythmias.

Interactions
Drug-drug. Aminoglycosides, anesthetics: Prolongs or enhances muscle weakness. Use together cautiously.
Cardiac glycosides: Increase cardiac sensitivity to edrophonium. Use together cautiously.
Cholinergic drugs: Causes additive toxicity. Avoid use together.
Corticosteroids: Decrease cholinergic effects of edrophonium; when corticosteroids are stopped, cholinergic effects may increase, possibly affecting muscle strength. Watch for lack of drug effect.
Ganglionic blockers such as mecamylamine: May lead to a critical blood pressure decrease. Avoid use together.
Magnesium: Causes direct depressant effect on skeletal muscle. Avoid use together.
Procainamide, quinidine: May reverse cholinergic effect of edrophonium on muscle. Use together cautiously.
Succinylcholine: Prolongs respiratory depression from plasma esterase inhibition. Avoid use together.
Drug-herb. Jaborandi tree, pill-bearing spurge: Causes additive effect and increases risk of toxicity. Tell patient to use cautiously.

Adverse reactions
CNS: seizures, weakness.
CV: hypotension, bradycardia, AV block, cardiac arrest.
EENT: excessive lacrimation, diplopia, miosis, conjunctival hyperemia.
GI: nausea, vomiting, diarrhea, abdominal cramps, dysphagia, excessive salivation.
GU: urinary frequency, incontinence.
Musculoskeletal: dysarthria, muscle cramps, muscle fasciculation.
Respiratory: paralysis of muscles of respiration, central respiratory paralysis, bronchospasm, laryngospasm, increased bronchial secretions.
Skin: diaphoresis.

Effects on lab test results
None reported.

Overdose and treatment
Signs and symptoms of overdose include muscle weakness, nausea, vomiting, diarrhea, blurred vision, miosis, excessive tearing, bronchospasm, increased bronchial secretions, hypotension, incoordination, excessive sweating, cramps, fasciculations, paralysis, bradycardia or tachycardia, excessive salivation, and restlessness or agitation. Muscles first weakened by overdose include neck, jaw, and pharyngeal muscles, followed by muscle weakening of the shoulder, arms, pelvis, outer eye, and legs.
 Discontinue drug immediately. Support respiration; bronchial suctioning may be performed. Atropine may be given to block the muscarinic effects of edrophonium but won’t counter the paralytic effects of the drug on skeletal muscle. Avoid atropine overdose because it may lead to bronchial plug formation.

Special considerations
• When giving edrophonium to differentiate myasthenic crisis from cholinergic crisis, evaluate patient’s muscle strength closely.
• For easier administration, use a tuberculin syringe with an I.V. needle.
• Always have atropine sulfate injection readily available as an antagonist for the muscarinic effects of edrophonium.
Pregnant patients
• Drug may cause uterine irritability and induce premature labor when given I.V. to patients near term.
Breast-feeding patients
• Safety hasn’t been established. Breast-feeding women should avoid edrophonium.
Pediatric patients
• Children may require I.M. administration; with this route, drug effects may be delayed for 2 to 10 minutes.
Geriatric patients
• Elderly patients may be more sensitive to effects of this drug. Use cautiously.

Patient education
• Tell patient that adverse effects of drug will be transient because of its short duration of effect.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use