Pyridostigmine

Pyridostigmine is a reversible cholinesterase inhibitor of the carbamate class, commonly administered as pyridostigmine bromide. It is a quaternary ammonium compound that does not readily cross the blood–brain barrier, so central nervous system effects are limited. By inhibiting acetylcholinesterase, it increases acetylcholine at the neuromuscular junction, improving transmission in conditions with reduced acetylcholine availability.

Pyridostigmine is the first-line symptomatic therapy for many people with myasthenia gravis, used to improve muscle strength and endurance in combination with immunosuppressants in some regimens. It can also be used as a pretreatment to help protect against organophosphate nerve agents in certain military and civilian settings.

Administration and pharmacokinetics: It is typically given orally, in divided doses taken with meals to reduce gastrointestinal side effects. The onset of improvement occurs within 15–60 minutes; duration is several hours. A parenteral formulation exists but oral administration is standard. The compound is poorly absorbed into the central nervous system and is largely excreted by the kidneys; the half-life is roughly 3–4 hours.

Safety and considerations: Common adverse effects are muscarinic (salivation, diarrhea, abdominal cramps, sweating), nicotinic (muscle cramps, fasciculations), and bradycardia. Overdosing can cause a cholinergic crisis; symptoms overlap with a myasthenic crisis, requiring clinical assessment and possible atropine for muscarinic symptoms or pralidoxime for organophosphate exposure. Cautions include peptic ulcer disease, asthma, gastrointestinal or urinary tract obstruction, and interactions with other cholinergic or anticholinergic drugs. Use in pregnancy and lactation should be discussed with a clinician.