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Acetylcholinesterase Inhibitor — Myasthenia Gravis Pregnancy: Use with caution — neonatal myasthenia from maternal antibody transfer; pyridostigmine itself does not cross placenta significantly

Pyridostigmine

Brand names: Mestinon

Adult dose

Dose: 30–120 mg every 3–6 hours; usual total 300–600 mg/day
Route: Oral
Frequency: Every 3–6 hours (typically 4–6 doses/day)
Max: 960 mg/day
First-line symptomatic treatment for myasthenia gravis (MG). Inhibits acetylcholinesterase at the neuromuscular junction — increases ACh and improves neuromuscular transmission. Titrate dose to symptoms — ocular, bulbar, and limb weakness. Does not alter disease course (immunosuppressants needed for remission).

Paediatric dose

Dose: 1 mg/kg
Route: Oral
Frequency: Every 4–6 hours
Max: 7 mg/kg/day
Neonatal myasthenia: 1–2 mg/kg/dose (from maternal antibody transfer). Children: 1 mg/kg every 4–6 hours.

Dose adjustments

Renal

Reduce dose in renal impairment — renally excreted. Monitor for cholinergic excess.

Hepatic

No specific adjustment.

Paediatric weight-based calculator

Neonatal myasthenia: 1–2 mg/kg/dose (from maternal antibody transfer). Children: 1 mg/kg every 4–6 hours.

Clinical pearls

  • Cholinergic crisis vs. myasthenic crisis: both cause weakness. Cholinergic crisis has SLUDGE features + pupillary constriction — stop pyridostigmine and give atropine. Myasthenic crisis: worsening despite medication — need IV immunoglobulin or plasmapheresis.
  • Always inform anaesthetist before surgery — suxamethonium is contraindicated; non-depolarising NMBs require much higher doses due to competitive antagonism
  • Antidote for cholinergic crisis/overdose: atropine 1–2 mg IV titrated to effect

Contraindications

  • Mechanical bowel or urinary obstruction
  • Depolarising neuromuscular blockers (suxamethonium — prolonged block)

Side effects

  • Cholinergic excess: SLUDGE (Salivation, Lacrimation, Urination, Defaecation, GI distress, Emesis)
  • Bradycardia
  • Muscle fasciculations
  • Miosis
  • Bronchospasm (high doses)
  • Cholinergic crisis (overdose — muscle weakness paradoxically worsens)

Interactions

  • Suxamethonium (prolongs depolarising block — tell anaesthetist before surgery)
  • Non-depolarising NMB agents (antagonism — higher doses needed)
  • Beta-blockers (additive bradycardia)
  • Corticosteroids (initially worsen MG weakness — start low and titrate slowly)

Monitoring

  • Clinical MG assessment (MGFA classification)
  • Forced vital capacity (FVC) — respiratory muscle weakness
  • Cholinergic side effects

Reference: BNFc; BNF 90; MGNZ/UK Myasthenia Gravis Foundation Guidelines; BNFc. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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