edrophonium chloride

ed·ro·pho·ni·um chloride (dr-fn-m)

n.

A competitive antagonist of skeletal muscle relaxants, such as curare derivatives, used as an antidote for curariform drugs, as a diagnostic agent in myasthenia gravis, and in myasthenic crisis.

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edrophonium chloride

[ed′rōfō′nē·əm]

a cholinesterase inhibitor that acts as an antidote to curare and other nondepolarizing neuromuscular blockers and is an aid in the diagnosis of myasthenia gravis.

indications It is prescribed to reverse neuromuscular blockade, to treat curare toxicity, and to aid in the diagnosis of suspected myasthenia gravis.

contraindications Obstruction of the GI or urinary tract, hypotension, bradycardia, or known hypersensitivity to this drug prohibits its use. Should be used with caution in patients with asthma and those taking cardiac glycosides.

adverse effects Among the most serious adverse effects are respiratory paralysis, hypotension, bradycardia, and bronchospasm.

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edrophonium chloride

Enlon, Tensilon

Pharmacologic class: Anticholinesterase

Therapeutic class: Diagnostic drug, muscle stimulant, antidote

Pregnancy risk category C

Action

Reversibly inhibits cholinesterase, blocking acetylcholine from its release sites in parasympathetic and somatic efferent nerves and increasing acetylcholine concentration in synapses

Availability

Injection: 10 mg/ml in 1-ml ampules and in 10-ml and 15-ml vials

⊘Indications and dosages

➣ Diagnostic aid in myasthenia gravis (Tensilon test)

Adults: 1 to 2 mg I.V. over 15 to 30 seconds; if no response occurs within 45 seconds, give 8 mg. Alternatively, 10 mg I.M.

Children weighing more than 34 kg (75 lb): 2 mg I.V.; if no response occurs within 45 seconds, give 1 mg q 45 seconds, to a maximum of 10 mg. Alternatively, 5 mg I.M.

Children weighing 34 kg (75 lb) or less: 1 mg I.V.; if no response occurs within 45 seconds, give 1 mg q 45 seconds, to a maximum of 5 mg. Alternatively, 2 mg I.M.

➣ To differentiate myasthenic crisis from cholinergic crisis

Adults: 1 mg I.V.; if no response occurs in 1 minute, repeat dose once. Increased muscle strength confirms myasthenic crisis; weakness or no increase in muscle strength confirms cholinergic crisis.

➣ Antidote for curare to reverse nondepolarizing neuromuscular blocking action

Adults: 10 mg I.V. given over 30 to 45 seconds. Repeat dose q 5 to 10 minutes p.r.n. to a maximum of 40 mg.

Contraindications

• Hypersensitivity to drug or sulfites
• Mechanical GI or urinary tract obstruction
• Peritonitis
• Breastfeeding

Precautions

Use cautiously in:
• bronchial asthma, peptic ulcer, bradycardia, arrhythmias, vagotonia, hyperthyroidism, epilepsy, recent coronary occlusion
• pregnant patients.

Administration

• Withdraw anticholinesterase drugs at least 8 hours before test.
☞ Keep atropine (edrophonium antidote) readily available.
☞ Keep advanced life-saving equipment on hand during administration, because drug may cause respiratory distress.
☞ Administer only when continuous ECG monitoring is available.
• Know that drug may be given undiluted and that maximum concentration is 10 mg/ml.
• Frequently assess muscle strength when giving drug for diagnostic or differentiating indications.

Route	Onset	Peak	Duration
I.V.	<1 min	Unknown	5-20 min
I.M.	2-10 min	Unknown	10-40 min

Adverse reactions

CNS: asthenia, dysarthria, dysphonia, dizziness, drowsiness, headache, syncope, loss of consciousness, seizures

CV: hypotension, thrombophlebitis (with I.V. use), atrioventricular block, cardiac arrest, bradycardia

EENT: lacrimation, diplopia, miosis, conjunctival hyperemia

GI: nausea, vomiting, diarrhea, abdominal cramps, increased salivation, dysphagia

GU: urinary frequency or incontinence

Musculoskeletal: muscle cramps, fasciculations

Respiratory: increased secretions, dyspnea, respiratory muscle paralysis, respiratory depression, central respiratory paralysis, respiratory arrest, bronchospasm, laryngospasm

Skin: rash, diaphoresis, flushing

Other: anaphylaxis

Interactions

Drug-drug. Aminoglycosides: prolonged or increased muscle weakness

Cholinergics: increased cholinergic effects that mimic myasthenia weakness

Corticosteroids, magnesium, procainamide, quinidine: antagonism of cholinergic effects

Depolarizing neuromuscular blockers: increased neuromuscular blockade, prolonged respiratory depression

Local and general anesthetics: antagonism of cholinergic effects

Drug-diagnostic tests. Urine cannabinoid test: false-positive result

Drug-food. High-fat meals: decreased drug absorption

Drug-herbs. Jaborandi, pill-bearing spurge: additive effects

Patient monitoring

☞ When giving as diagnostic test for myasthenia gravis, monitor closely for cholinergic crisis (skeletal muscle fasciculations and increased muscle weakness, especially in respiratory muscles) after 2-mg dose. If cholinergic crisis occurs, discontinue drug and give atropine I.V. as prescribed.
☞ Assess for bradycardia, hypotension, and cardiac arrest.
• Monitor I.V. site closely.
• Observe for nausea and vomiting. Give antiemetics, as prescribed.

Patient teaching

• Tell patient that increased muscle strength is a positive response to drug.
• Advise patient to report vision changes.
• Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration and alertness.
• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, foods, and herbs mentioned above.