Mestinon

Action

Prevents acetylcholine destruction, resulting in stronger contractions of muscles weakened by myasthenia gravis or curare-like neuromuscular blockers

Availability

Injection: 5 mg/ml

Syrup: 60 mg/5 ml

Tablets: 60 mg

Tablets (extended-release): 180 mg

Indications and dosages

➣ Myasthenia gravis

Adults: 600 mg P.O. given over 24 hours, with doses spaced for maximum symptom relief. For myasthenic crisis, 2 mg or 1/30 of oral dose I.M. or very slow I.V. q 2 to 3 hours.

➣ Postoperative reversal of nondepolarizing neuromuscular blockers

Adults: 10 to 20 mg slow I.V. injection (range is 0.1 to 0.25 mg/kg) with or immediately after 0.6 to 1.2 mg atropine sulfate I.V.

Dosage adjustment

• Renal impairment

• Seizure disorders

Off-label uses

• Myasthenia gravis in children

• Constipation in patients with Parkinson's disease

• Nerve agent prophylaxis

Contraindications

• Hypersensitivity to drug or bromides

• Mechanical intestinal or urinary tract obstruction

Precautions

Use cautiously in:

• seizure disorders, bronchial asthma, coronary occlusion, arrhythmias, bradycardia, hyperthyroidism, peptic ulcer, vagotonia, cholinergic crisis

• pregnant or breastfeeding patients

• children (safety and efficacy not established).

Administration

See Don't exceed I.V. injection rate of 1 mg/minute.

See Don't give concurrently with other anticholinesterase drugs.

• Have atropine available for use in emergencies.

Adverse reactions

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

CV: decreased cardiac output leading to hypotension, bradycardia, nodal rhythm, atrioventricular block, cardiac arrest, arrhythmias

EENT: diplopia, lacrimation, miosis, spasm of accommodation, conjunctival hyperemia

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

GU: urinary frequency, urgency, or incontinence

Musculoskeletal: muscle weakness, fasciculations, and cramps; joint pain

Respiratory: increased pharyngeal and tracheobronchial secretions, dyspnea, central respiratory paralysis, respiratory muscle paralysis, laryngospasm, bronchospasm, bronchiolar constriction

Skin: diaphoresis, flushing, rash, urticaria

Other: thrombophlebitis at I.V. site, cholinergic crisis, anaphylaxis

Interactions

Drug-drug. Aminoglycosides: potentiation of neuromuscular blockade

Anesthetics (general and local), antiarrhythmics: decreased anticholinesterase effects

Atropine, belladonna derivatives: suppression of parasympathomimetic GI symptoms (leaving only fasciculations and voluntary muscle paralysis as signs of anticholinesterase overdose)

Corticosteroids: decreased anticholinesterase effects; after corticosteroid withdrawal, increased anticholinesterase effects

Ganglionic blockers (such as mecamy-lamine): increased anticholinesterase effects

Magnesium: antagonism of beneficial anticholinesterase effects

Nondepolarizing neuromuscular blockers (atropine, pancuronium, tubocurarine): antagonism of neuromuscular blockade and reversal of muscle relaxation after surgery (with parenteral pyridostigmine)

Other anticholinesterase drugs: in patients with myasthenia gravis, symptoms of anticholinesterase overdose that mimic underdose, causing patient's condition to worsen

Succinylcholine: increased and prolonged neuromuscular blockade (including respiratory depression)

Patient monitoring

• Assess patient's response to each dose.

• Monitor vital signs, ECG, and cardiovascular and respiratory status.

See Assess for signs and symptoms of overdose, which indicate cholinergic crisis.

Patient teaching

• If patient is using syrup, advise him to pour it over ice.

• Instruct patient using extended-release tablets not to crush them.

See Teach patient to recognize and promptly report signs and symptoms of overdose, including muscle fasciculations, sweating, excessive salivation, and constricted pupils.

• Tell patient drug may cause headache and muscle cramps. Encourage him to discuss activity recommendations and pain management with prescriber.

• Advise patient to monitor and report his response to ongoing therapy so that optimal dosage can be determined.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs mentioned above.