Pyridostigmine

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.