Acetylcholine esterase inhibitors (of which pyridostig-
mine is the most widely used) inhibit the breakdown of
ACh at the neuromuscular junction. This increases the
availability of ACh to stimulate AChR and facilitates
muscle activation and contraction. These drugs are
most helpful as initial therapy in newly diagnosed pa-
tients with MG, and as sole long-term treatment of
milder disease.
These drugs are usually well tolerated at standard
doses of up to 60 mg five times per day. Adverse effects
are caused by the increased concentration of ACh at
both nicotinic and muscarinic synapses. The common
muscarinic effects are gut hypermotility (stomach
cramps, diarrhoea), increased sweating, excessive
respiratory and gastrointestinal secretions [12,13], and
bradycardia. The main nicotinic adverse effects are
muscle fasciculations and cramps.