Mestinon

Mestinon (Pyridostigmine) is used for treating myasthenia gravis.

Product dosage: 60mg
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Synonyms Amiasten Piridostigmina Pyridostigminum Dostirav Regonol Becilan Distinon

Mestinon (pyridostigmine bromide) is a first-line acetylcholinesterase inhibitor medication central to the symptomatic management of myasthenia gravis. It functions by slowing the breakdown of acetylcholine, the critical neurotransmitter responsible for transmitting signals between nerves and muscles. This action effectively increases the availability of acetylcholine at the neuromuscular junction, leading to improved muscle strength and endurance. Its predictable pharmacokinetic profile and well-established efficacy make it a cornerstone therapy for patients and clinicians managing this chronic autoimmune condition.

Features

• Active Pharmaceutical Ingredient: Pyridostigmine Bromide
• Available Formulations: Immediate-release oral tablets (60 mg), extended-release oral tablets (180 mg), and oral syrup (60 mg/5 mL)
• Pharmacologic Class: Reversible Anticholinesterase Agent
• Mechanism of Action: Inhibits the hydrolysis of acetylcholine by acetylcholinesterase
• Onset of Action: Typically 30-45 minutes for immediate-release formulations
• Duration of Effect: Approximately 3-4 hours for immediate-release; 6-8 hours for extended-release formulations
• Bioavailability: Poor and variable gastrointestinal absorption (approximately 10-20%)
• Protein Binding: Minimal
• Metabolism: Undergoes hydrolysis in the gastrointestinal tract and liver
• Elimination Half-life: Approximately 1-2 hours
• Excretion: Primarily renal (unchanged drug and metabolites)

Benefits

• Rapid Improvement in Muscle Strength: Directly addresses the core pathophysiology of myasthenia gravis, leading to a noticeable reduction in ptosis, diplopia, and difficulty with chewing, swallowing, and speaking.
• Enhanced Functional Capacity and Quality of Life: By mitigating muscle weakness and fatigability, it enables patients to perform activities of daily living with greater independence and reduced exertion.
• Flexible Dosing Regimens: The availability of immediate-release and extended-release formulations allows for tailored treatment schedules, including the use of time-span tablets to cover overnight symptoms.
• Well-Established Safety Profile: Decades of clinical use have provided a comprehensive understanding of its side effect profile and management strategies.
• Predictable Pharmacodynamic Response: The dose-response relationship is generally consistent, allowing neurologists to titrate effectively based on clinical assessment.
• Acts as a Diagnostic Tool: The Tensilon test (using edrophonium, a related agent) or a clear clinical response to Mestinon can support the diagnosis of myasthenia gravis.

Common use

Mestinon is primarily indicated for the treatment of myasthenia gravis, an autoimmune disorder characterized by autoantibodies that attack postsynaptic acetylcholine receptors at the neuromuscular junction. It is used for symptomatic control to improve muscle strength and reduce fatigability. It is suitable for both ocular and generalized forms of the disease. It may also be used perioperatively to manage muscle strength. Furthermore, it is occasionally used off-label to reverse the effects of non-depolarizing neuromuscular blocking agents after surgery and to treat orthostatic hypotension and certain types of urinary retention, owing to its parasympathomimetic effects.

Dosage and direction

Dosage is highly individualized and must be titrated under the supervision of a neurologist based on clinical response and tolerability.

• Myasthenia Gravis (Adults): The typical initial dose of immediate-release tablets is 30-60 mg administered orally every 3-4 hours while awake. The usual maintenance dosage ranges from 60 mg to 150 mg every 3-4 hours, with total daily doses typically between 600 mg and 1500 mg, divided into 5-6 doses. The dosing schedule is often aligned with meal times to leverage the symptomatic relief during eating.
• Extended-Release Tablets (Timespan): Reserved for nighttime use only to control symptoms while sleeping. The typical dose is 180 mg at bedtime. It is crucial to note that extended-release tablets must never be crushed or chewed and are not to be used for daytime symptom control due to the risk of overdose.
• Pediatric Population: Dosage is based on body weight or surface area. A common starting dose is 7 mg/kg/day or 200 mg/m²/day, divided into 5-6 doses.
• Administration: Tablets should be taken with a full glass of water, with or without food. If gastrointestinal side effects occur, administration with food or milk may improve tolerability.

Precautions

Patients should be closely monitored for both under-dosing (myasthenic weakness) and over-dosing (cholinergic crisis). Caution is advised in patients with asthma, chronic obstructive pulmonary disease (COPD), or other respiratory conditions due to the potential for increased bronchial secretions and bronchospasm. It should be used with care in patients with bradycardia, hypotension, hyperthyroidism, peptic ulcer disease, or recent coronary occlusion. Renal impairment necessitates dosage adjustment, as the drug and its metabolites are renally excreted. Patients should be advised that the medication’s effects may be diminished by infections, stress, surgery, or other medications.

Contraindications

Mestinon is contraindicated in patients with a known hypersensitivity to pyridostigmine bromide or any components of the formulation. Its use is also contraindicated in cases of mechanical intestinal or urinary obstruction, a history of which is a absolute contraindication due to the drug’s stimulatory effect on smooth muscle.

Possible side effect

Side effects are primarily related to its parasympathomimetic activity (muscarinic and nicotinic effects).

• Common (Muscarinic): Nausea, vomiting, diarrhea, abdominal cramps, increased salivation, increased bronchial secretions, sweating, lacrimation.
• Less Common (Nicotinic): Muscle cramps, fasciculations, weakness (can be a sign of cholinergic crisis).
• Serious: Bradycardia, hypotension, syncope, respiratory depression or failure (in cholinergic crisis), bronchospasm.

A cholinergic crisis, resulting from overdose, is a medical emergency characterized by severe muscarinic and nicotinic effects, including increased weakness, and must be differentiated from a myasthenic crisis.

Drug interaction

Concurrent use with other cholinergic agents (e.g., bethanechol) will have additive effects and toxicity. Anticholinergic agents (e.g., atropine, glycopyrrolate) may counteract the muscarinic side effects of Mestinon but can mask the early signs of a cholinergic crisis. Aminoglycoside antibiotics, magnesium salts, and antiarrhythmic drugs like procainamide or quinidine can antagonize the neuromuscular effects of Mestinon, potentially worsening weakness. Corticosteroids may initially exacerbate myasthenic weakness, requiring careful monitoring when initiating therapy. Succinylcholine may be potentiated and its duration prolonged, while the effects of non-depolarizing neuromuscular blockers may be antagonized.

Missed dose

If a dose is missed, it should be taken as soon as it is remembered. However, if it is almost time for the next scheduled dose, the missed dose should be skipped, and the regular dosing schedule resumed. Patients should never double the dose to make up for a missed one, as this significantly increases the risk of a cholinergic crisis.

Overdose

Overdose constitutes a medical emergency due to the high risk of developing a cholinergic crisis. Symptoms include severe nausea, vomiting, diarrhea, excessive salivation and sweating, blurred vision, bradycardia, hypotension, muscle twitching and increasing weakness, and respiratory paralysis. Supportive measures, including securing the airway and providing assisted ventilation, are paramount. Atropine sulfate is the specific antidote for the muscarinic effects (e.g., bradycardia, secretions) but will not counteract the neuromuscular blockade (nicotinic effects) which is the primary cause of respiratory failure.

Storage

Store at room temperature (20°C to 25°C or 68°F to 77°F), in a tight, light-resistant container. Keep the bottle tightly closed to protect from moisture. Keep all medications out of the reach of children and pets. Do not use after the expiration date printed on the label.

Disclaimer

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your neurologist or other qualified health provider with any questions you may have regarding a medical condition or medication. Never disregard professional medical advice or delay in seeking it because of something you have read here. The content has been compiled from various pharmacological resources but may not be exhaustive or fully updated.

Reviews

• Clinical Neurologist, 20 years experience: “Mestinon remains the bedrock of symptomatic therapy for myasthenia gravis. Its rapid onset allows patients to gain immediate control over debilitating symptoms like ptosis and dysphagia. The key is careful, individualized titration to find the minimal effective dose that maximizes function while minimizing cholinergic side effects. The availability of a syrup formulation is invaluable for our pediatric and dysphagic patients.”
• Patient with Generalized MG, 5 years on therapy: “It’s not a cure, but it gives me back hours of my day. I plan my doses around meals and important activities. The side effects were tough at first—stomach cramps mainly—but they settled down after a few weeks. It’s a constant balancing act, but without it, I wouldn’t be able to work or care for my family.”
• Pharmacist Specialist in Neurology: “Patient education is critical with Mestinon. We spend considerable time ensuring patients understand the difference between under-treatment and over-treatment, the strict instructions for the timespan tablets, and the signs of a cholinergic crisis. It’s a powerful drug that, when used correctly, dramatically improves quality of life.”