16 December 2019

Physostigmine – a natural carbamate derivate and an indole alkaloid


Physostigmine has a role as a miotic, a cholinesterase inhibitor and an antidote to curare poisoning. It is a highly toxic parasympathomimetic alkaloid, specifically, a reversible cholinesterase inhibitor. It occurs naturally in the Calabar bean.

Physostigmine is a secondary metabolites of Physostigma venenosum (Calabar bean). The plant is widely used for the treatment of anticholinergic syndrome, myasthenia gravis, glaucoma and delayed gastric emptying, which mainly associated with its physostigmine content. In ancient times, the calabar bean is used to indicate guilt and, at the same time, to be a rightful punishment flowed by the deadly effect on the person swallowed it.


Figure: Left – Physostigma venenosum (Calabar bean) and right – structural representation of physostigmine.

Physostigmine is a reversible cholinesterase inhibitor alkaloid. It delays the breakdown of acetylcholine and increases its concentration at the receptor, which results in indirect parasympathomimetic effect. The symptom includes influencing communication between the nerves and muscles, and resulting in copious salivation, seizures, loss of control over the bladder and bowels, and eventually loss of control over the respiratory system, causing death by asphyxiation. Other side effects may also include nausea, vomiting, diarrhea, anorexia, dizziness, headache, stomach pain, sweating and dyspepsia.

In bodily condition, physostigmine undergoes hydrolyses in water and releases the metabolite eseroline, which is neurotoxic to humans. The overdose can cause cholinergic syndrome as a result of respiratory arrest and paralysis of the heart, which subsequently leads to death.


CAS No: 57-47-6


  • Somani SM, Kutty RK and Krishna G, 1990. Eseroline, a metabolite of physostigmine, induces neuronal cell death. Toxicology and Applied Pharmacology, 106 (1): 28-37.
  • Čolović MB, Krstić DZ, Lazarević-Pašti TD, Bondžić AM, and Vasić VM, 2013. Acetylcholinesterase Inhibitors: Pharmacology and Toxicology. Neuropharmacology, 11: 315-335.
  • Proudfoot A, 2006. The Early Toxicology of Physostigmine. Toxicological Reviews volume 25: 99–138.
  • https://pubchem.ncbi.nlm.nih.gov/compound/119198
  • https://en.wikipedia.org/wiki/Physostigmine