MESTINON
Clinical safety rating: caution
Comprehensive clinical and safety monograph for MESTINON (MESTINON).
Inhibits acetylcholinesterase, preventing breakdown of acetylcholine and increasing its concentration at cholinergic synapses, thereby enhancing neuromuscular transmission.
| Metabolism | Primarily metabolized by plasma esterases via hydrolysis; minor hepatic metabolism. |
| Excretion | Renal excretion of unchanged drug and metabolites accounts for approximately 80-90% of elimination, with a small fraction (10-20%) eliminated in feces via biliary secretion. |
| Half-life | The terminal elimination half-life is approximately 1.5 to 2 hours in adults. In patients with renal impairment, half-life may be prolonged (up to 6-10 hours in severe impairment), necessitating dose adjustment. |
| Protein binding | Approximately 30–40% bound to plasma proteins, primarily albumin. |
| Volume of Distribution | 0.6–1.4 L/kg (approximately 42–98 L in a 70 kg adult). The wide distribution reflects extensive tissue uptake, including voluntary muscles. |
| Bioavailability | Oral: 10–20% (due to extensive first-pass metabolism); Intramuscular: approximately 100% (complete absorption). |
| Onset of Action | Oral: 30–45 minutes; Intramuscular: 15–30 minutes; Intravenous: 1–5 minutes. |
| Duration of Action | Oral: 3–6 hours; Intramuscular: 2–4 hours; Intravenous: 1–2 hours. The duration is dose-dependent and shorter in patients with myasthenia gravis due to rapid clearance. |
Myasthenia gravis: 60-150 mg orally every 3-4 hours, up to 1.2 g/day. Extended-release: 180-540 mg orally once or twice daily.
| Dosage form | INJECTABLE |
| Renal impairment | CrCl 10-50 mL/min: administer 75% of normal dose every 6 hours. CrCl <10 mL/min: administer 50% of normal dose every 6 hours. |
| Liver impairment | No specific dose adjustment recommended; use with caution due to potential prolongation of effects. |
| Pediatric use | Neonates: 0.5-1 mg/kg IM or SC every 4-6 hours. Children: 7 mg/kg/day orally divided every 3-4 hours or 0.3-0.6 mg/kg IM every 4-6 hours. |
| Geriatric use | Start at lower end of dosing range; monitor for excessive muscarinic effects; adjust based on renal function and tolerability. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for MESTINON (MESTINON).
| Breastfeeding | Small amounts of pyridostigmine are excreted into breast milk; approximate M/P ratio is 0.3–0.6. Clinical relevance is low, but monitor infant for cholinergic effects (diarrhea, muscle weakness, excessive salivation). Compatible with breastfeeding with caution. |
| Teratogenic Risk | FDA Pregnancy Category C. Animal reproduction studies have not been conducted. It is not known whether pyridostigmine can cause fetal harm when administered to a pregnant woman. Risks by trimester: First trimester – potential for teratogenicity unknown; limited human data. Second and third trimesters – use only if clearly needed; may cause transient neonatal myasthenia gravis (muscle weakness, respiratory distress) if used near term. |
■ FDA Black Box Warning
None.
| Serious Effects |
["Hypersensitivity to pyridostigmine or bromides","Mechanical intestinal or urinary obstruction"]
| Precautions | ["May cause bradycardia, hypotension, and seizures; monitor cardiac function.","Caution in patients with asthma, bradyarrhythmias, or peptic ulcer disease.","Overdosage can lead to cholinergic crisis characterized by muscle weakness, paralysis, and respiratory failure."] |
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| Fetal Monitoring | Monitor maternal vital signs, respiratory function, and signs of cholinergic crisis (e.g., bradycardia, hypotension, excessive secretions). Assess fetal growth and well-being via ultrasound and non-stress tests in third trimester. Neonatal assessment for transient myasthenic symptoms postpartum. |
| Fertility Effects | No known adverse effects on fertility. Pyridostigmine is not known to impair fertility in males or females. However, underlying disease (myasthenia gravis) may impact fertility. |