Document from `Drug Information Handbook'
Brand Names
Mestinon ; Regonol
Therapeutic Category
Antidote, Neuromuscular Blocking Agent Cholinergic Agent
Use
Symptomatic treatment of myasthenia gravis; also used as an antidote for nondepolarizing neuromuscular blockers; not a cure; patient may develop resistance to the drug.
Pregnancy Risk Factor
Contraindications
Hypersensitivity to pyridostigmine, bromides, or any component; GI or GU obstruction
Warnings/Precautions
Use with caution in patients with epilepsy, asthma, bradycardia, hyperthyroidism, cardiac arrhythmias, or peptic ulcer; adequate facilities should be available for
cardiopulmonary resuscitation when testing and adjusting dose for myasthenia gravis; have atropine and epinephrine ready to treat hypersensitivity reactions; overdosage may result in cholinergic crisis, this must be distinguished from myasthenic crisis; anticholinesterase insensitivity can develop for brief or prolonged periods.
Adverse Reactions
>10%: Gastrointestinal: Diarrhea, nausea, stomach cramps, mouth watering Miscellaneous: Increased sweating
1% to 10%: Genitourinary: Urge to urinate Ocular: Small pupils, lacrimation Respiratory: Increased bronchial secretions
<1%: Cardiovascular: Bradycardia, A-V block Central nervous system: Seizures, headache, dysphoria, drowsiness, weakness Local: Thrombophlebitis
Neuromuscular & skeletal: Muscle spasms Ocular: Miosis, diplopia Respiratory: Laryngospasm, respiratory paralysis
Miscellaneous: Hypersensitivity, hyper-reactive cholinergic responses
Overdosage/Toxicology
Symptoms of overdose include muscle weakness, blurred vision, excessive sweating, tearing and salivation, nausea, vomiting, diarrhea, hypertension, bradycardia,
paralysis. Atropine is the treatment of choice for intoxications manifesting with significant muscarinic
symptoms. Atropine I.V. 2-4 mg every 3-60 minutes (or 0.04-0.08 mg I.V. every 5-60 minutes if needed for children) should be repeated to control symptoms and then continued as needed for 1-2 days following the acute ingestion.
Drug Interactions
Increased effect of depolarizing neuromuscular blockers
(succinylcholine) Increased toxicity with edrophonium
Stability
Protect from light
Mechanism of Action
Inhibits destruction of acetylcholine by acetylcholinesterase which facilitates transmission of impulses across myoneural junction
Pharmacodynamics/Kinetics
Onset of action: Oral, I.M.: Within 15-30 minutes
I.V. injection: Within 2-5 minutes
Absorption: Oral: Very poor (10% to 20%) from GI tract Metabolism: In the liver
Usual Dosage
Normally, sustained release dosage form is used at bedtime for patients who complain of morning
weakness
Myasthenia gravis:
Oral: Children: 7 mg/kg/day in 5-6 divided doses
Adults: Initial: 60 mg 3 times/day with maintenance dose
ranging from 60 mg to
1.5 g/day; sustained release formulation should be dosed at
least every 6 hours
(usually 12-24 hours)
I.M., I.V.:
Children: 0.05-0.15 mg/kg/dose (maximum single dose: 10 mg)
Adults: 2 mg every 2-3 hours or 1/30th of oral dose
Reversal of nondepolarizing neuromuscular blocker: I.M., I.V.:
Children: 0.1-0.25 mg/kg/dose preceded by atropine
Adults: 10-20 mg preceded by atropine
Test Interactions
aminotransferase amylase
Patient Information
Side effects are generally due to exaggerated pharmacologic effects; most
common side effects are
salivation and muscle fasciculations; notify physician if nausea, vomiting,
muscle weakness, severe
abdominal pain, or difficulty breathing occurs
Nursing Implications
Do not crush sustained release drug product; observe for cholinergic
reactions, particularly when
administered I.V.
Dosage Forms
Injection: 5 mg/mL (2 mL, 5 mL)
Syrup (raspberry flavor): 60 mg/5 mL (480 mL)
Tablet: 60 mg
Tablet, sustained release: 180 mg
Selected Readings
1.Dunn MA and Sidell FR, "Progress in Medical Defense Against Nerve
Agents," JAMA ,
1989, 262(5):649-52.
2.Keeler JR, Hurst CG, and Dunn MA, "Pyridostigmine Used as a Nerve Agent
Pretreatment
Under Wartime Conditions," JAMA , 1991, 266(5):693-5.
3.Sidell FR and Borak J, "Chemical Warfare Agents: II. Nerve Agents," Ann
Emerg Med ,
1992, 21(7):865-71.
Copyright (1995 to present) Lexi-Comp, Inc.
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