Tensilon

Tensilon

trademark for edrophonium chloride; used in the diagnosis of myasthenia gravis, known as the Tensilon test.

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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.