10.2.1 Drugs that enhance neuromuscular transmission

Prescribing Notes

• Anticholinesterase drugs enhance neuromuscular transmission in voluntary and involuntary muscle in myasthenia gravis. They prolong the action of acetylcholine by inhibiting the action of the enzyme acetylcholinesterase. Excessive dosage of these drugs can impair neuromuscular transmission and precipitate cholinergic crises by causing a depolarising block. This may be difficult to distinguish from a worsening myasthenic state.
• Muscarinic side-effects of anticholinesterases include increased sweating, increased salivary and gastric secretions, increased gastro-intestinal and uterine motility, and bradycardia. These parasympathomimetic effects are antagonised by atropine.
• Treatment for myasthenia gravis should only be initiated on specialist advice.
• An antimuscarinic (e.g. propantheline 15mg orally as required, up to 3 times daily or adjusted to individual circumstances) may be required to treat side-effects such as sweating, colic, excessive salivation and diarrhoea.