Physostigmine

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Summary

Physostigmine is a cholinesterase inhibitor, that leads to increased levels of acetylcholine by inhibiting its breakdown. Its primary clinical use is to counteract the anticholinergic effects of atropine poisoning. Physostigmine works peripherally but also centrally since it is able to cross the blood brain barrier. At high doses, watch out for adverse effects like cholinergic overstimulation.

Key Points

  • Physostigmine
    • Mechanism
      • Cholinesterase inhibitor (AChEI)
        • Increases ACh levels by blocking its breakdown
      • Crosses blood-brain-barrier
        • Works peripherally and centrally
        • Therefore, a good antidote for atropine poisoning since it can reverse central effects
    • Clinical Use
      • Treatment for atropine poisoning
        • Mnemonic: physostigmine “phyxes” atropine overdose
        • May also be used for other anticholinergic poisons, e.g. belladonna (nightshade) or jimson weed (datura)
      • Glaucoma
      • Myasthenia Gravis
        • Less preferred vs. neostigmine because it works centrally (e.g. off-target CNS effects)
    • 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