Pyridostigmine is a cholinesterase inhibitor used to treat Myasthenia Gravis by increasing peripheral acetylcholine levels. This increase in acetylcholine increases the strength of peripheral skeletal muscle contractions, effectively treating the muscle weakness seen in Myasthenia Gravis. Pyridostigmine is considered to be the first line treatment for Myasthenia Gravis because it acts on the peripheral nervous system only and is blocked from entering the central nervous system. Adverse effects to look out for in question stems include cholinergic overload.

Key Points

  • Pyridostigmine
    • Mechanism
      • Cholinesterase inhibitor
        • Increases ACh levels by inhibiting Acetylcholinesterase levels (indirect agonist)
      • Does not cross BBB (peripheral only)
        • Quaternary amine structure does not allow passage into brain
    • Clinical Use
      • Myasthenia Gravis (long-acting)
        • Increase in acetylcholine levels can help outcompete myasthenic antibodies at the neuromuscular junction
    • Adverse Effects
      • Cholinergic overstimulation
        • Via overstimulation of cholinergic receptors
          • Glands: sweating, salivation, and lacrimation
          • GI and GU: diarrhea, abdominal cramping, urination
          • Heart: bradycardia
          • Respiratory: bronchospasm
          • Musculoskeletal: skeletal muscle overexcitation
          • Eye: miosis
        • Can be treated with atropine or pralidoxime