Acetylcholinesterase Inhibitor — Myasthenia Gravis Pregnancy: Safety in pregnancy not established; experience in pregnant myasthenic patients has revealed no untoward effect on the course of pregnancy. Crosses the placenta — avoid excessive doses and monitor the newborn for possible effects. IV administration can induce uterine contraction (especially in late pregnancy). Only negligible amounts excreted in breast milk.

Pyridostigmine

Brand names: Mestinon

Pyridostigmine is a reversible acetylcholinesterase inhibitor used as first-line symptomatic treatment for myasthenia gravis.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Myasthenia gravis: 30 to 120 mg per dose

Route: Oral

Frequency: At intervals throughout the day when maximum strength is needed (e.g. on rising and before mealtimes); duration of action 3-4 hours in the daytime, up to 6 hours for a bedtime dose

Myasthenia gravis (adults): total daily dose usually in the range of 5-20 tablets (each tablet 60 mg), but higher doses may be needed according to dose titration. Paralytic ileus and post-operative urinary retention (adults): usual dose 1-4 tablets (60-240 mg) per day, frequency varied to patient need. Paediatric myasthenia gravis (not a per-kg dose): children under 6 years initial 30 mg (half a tablet), children 6-12 years 60 mg (one tablet), increased gradually in 15-30 mg daily increments; total daily requirements usually 30-360 mg. Paediatric paralytic ileus / urinary retention: 15-60 mg per day. Verify paediatric dosing against a children's formulary. Take with water.

Dose adjustments

Renal

Pyridostigmine is mainly excreted unchanged by the kidney; lower doses may be required in patients with renal disease and treatment should be based on titration of dosage to effect.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance, bromides or to any of the excipients
Mechanical gastro-intestinal or urinary obstruction

Side effects

Muscarinic: nausea, vomiting, diarrhoea, abdominal cramps, increased peristalsis, increased bronchial secretion, salivation, bradycardia, miosis
Nicotinic: muscle spasms, fasciculation, muscular weakness
Arrhythmia (including bradycardia, tachycardia, AV block), Prinzmetal angina, syncope, hypotension
Increased lacrimation, accommodation disorders (e.g. blurred vision)
Rash, hyperhidrosis, urticaria; drug hypersensitivity

Interactions

Corticosteroids / immunosuppressant drugs: requirement for pyridostigmine may be decreased (a new addition of corticosteroids may initially aggravate myasthenia gravis symptoms)
Methylcellulose (and medicines containing it as an excipient) can completely inhibit absorption of pyridostigmine
Atropine and hyoscine antagonise the muscarinic effects; slower GI motility from these drugs may affect pyridostigmine absorption
Non-depolarising muscle relaxants (e.g. pancuronium, vecuronium): pyridostigmine antagonises their effect; may prolong the effect of depolarising relaxants (e.g. suxamethonium)
Aminoglycoside antibiotics, local and some general anaesthetics, antiarrhythmic agents and other drugs interfering with neuromuscular transmission may interact

Clinical monograph

How it works

It inhibits acetylcholinesterase at the neuromuscular junction, increasing the availability of acetylcholine at nicotinic receptors and so improving muscle strength.

Prescribing in practice

Overdose or excessive dosing can precipitate a cholinergic crisis with muscle weakness that mimics myasthenic deterioration; distinguishing the two is critical before escalating the dose.
It provides symptomatic relief only and does not modify the underlying autoimmune disease, so it is usually combined with immunosuppression in more severe disease.
Use cautiously in asthma, bradyarrhythmias and mechanical gastrointestinal or urinary obstruction, as cholinergic effects may worsen these conditions.

Monitoring

Monitor the clinical response in terms of muscle strength and watch for cholinergic adverse effects such as excessive salivation, abdominal cramps, diarrhoea and fasciculations.

Counselling the patient

Report increasing weakness, as this may signal either undertreatment or overtreatment and needs medical review rather than self-adjusting the dose.
Muscarinic side effects such as cramping, diarrhoea and increased saliva are common and can sometimes be managed with an antimuscarinic agent.
Take doses to coincide with periods when strength is most needed, such as before meals if swallowing is affected.

Evidence & guidelines

Pyridostigmine is the long-established standard symptomatic therapy for myasthenia gravis and is recommended as first-line treatment in international consensus guidance.

Reference: MGNZ/UK Myasthenia Gravis Foundation Guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways