Eserin

Eserin, commonly known as physostigmine or eserine, is a naturally occurring alkaloid that acts as a reversible acetylcholinesterase inhibitor. It is derived from the seeds of Physostigma venenosum, the Calabar bean, a plant native to West Africa. Physostigmine is a carbamate ester of a tertiary amine, and it belongs to the class of cholinesterase inhibitors.

Pharmacologically, eserine reversibly inhibits acetylcholinesterase, increasing the concentration of acetylcholine at cholinergic synapses. Its tertiary amine structure allows it to cross the blood–brain barrier, producing both central and peripheral effects. This dual action distinguishes it from many other acetylcholinesterase inhibitors that act mainly peripherally.

Medical uses have included treatment of open-angle glaucoma, where its miotic effect helps to improve aqueous humor outflow. It has also been employed as an antidote to anticholinergic (antimuscarinic) poisoning due to its ability to restore cholinergic function in the central and peripheral nervous systems. Because of safety concerns and the availability of more selective agents, physostigmine is now less commonly used for routine therapy, with alternatives favored in many situations.

Safety considerations are important. Adverse effects reflect cholinergic overstimulation and can include increased salivation, lacrimation, urination, defecation, miosis, bradycardia, hypotension, and, at high doses, seizures or coma. It is contraindicated in certain GI or urinary tract obstructions and in individuals with hypersensitivity; caution is advised in patients with asthma, COPD, peptic ulcer disease, or a history of seizures. The drug’s ability to affect the central nervous system requires careful dosing and monitoring.