Calabar Bean

Scientific Name(s): Physostigma venenosum Balf. f. Family: Fabaceae 1 (beans)

Common Name(s): Calabar bean , physostigma , ordeal bean , chop nut , esere nut , faba calabarica 2

Uses

Originally consumed in African ritual ordeals which killed many subjects, the bean produces alkaloids clinically used to contract the pupil, manage ocular pressure in glaucoma, reverse toxicity of certain other drugs, and treat myasthenia gravis.

Slideshow: Fact or Fiction? The Top 15 Osteoarthritis Myths

Dosing

Calabar bean has been widely studied as the pure alkaloid physostigmine. A typical dose for the pure alkaloid is 2 mg. There is no clinical evidence relating to the crude plant material or to an extract.

Contraindications

Contraindications have not yet been identified.

Pregnancy/Lactation

Documented adverse effects. Avoid use. 3

Interactions

None well documented.

Adverse Reactions

There are few reports on adverse reactions, as calabar bean is toxic to humans.

Toxicology

Calabar bean contains physostigmine, which is extremely toxic. It kills by affecting heart contractibility and inducing respiratory paralysis.

Botany

The calabar bean is the dried ripe seed of P. venenosum , a perennial woody climbing plant found on the banks of streams in West Africa. Vines of the plant extend more than 50 feet in the air, climbing high among the trees. 4 The plant bears showy purple flowers and seed pods that grow to about 6 inches in length. 4 Each pod contains from 2 to 3 seeds. 5 The dark brown seeds are about 1 inch wide and thick and have an extremely hard shell.

History

This plant is native to an area of Africa around Nigeria once known as Calabar. The plant is widely known in Africa because the seeds had been used as an “ordeal poison” to determine if a person was a witch or possessed by evil spirits. 6 When used for this purpose, the victim was made to ingest several beans; if the person regurgitated the beans and survived the “ordeal,” his innocence was proclaimed. Western settlers who were captured by native tribes and who underwent the “ordeal” soon learned not to chew the bean, but to swallow the kidney-shaped bean intact, thereby not permitting the release of the toxic constituents. The plant has been long recognized as a commercial source of the alkaloid physostigmine, first isolated in 1864.

Chemistry

The seeds contain the alkaloid physostigmine (eserine) in a concentration of about 0.15%, along with the related alkaloids eseramine, physovenine, calabatine, and geneserine, among others. These alkaloids are derived from a tryptophan precursor. On exposure to air, physostigmine oxidizes to a reddish compound, rubreserine, and therefore should be protected from air and light.

Uses and Pharmacology

Physostigmine (usually as the stable salicylate salt) ( Antilirium ) is an acetylcholinesterase inhibitor and, therefore, prolongs the neuronal activity of acetylcholine. It is used clinically to contract the pupil of the eye, often to counter the dilating effects of mydriatic drugs, reverse the CNS toxicity of anticholinergic drugs, including tricyclic antidepressants, and to manage intraocular pressure in patients with glaucoma. Physostigmine and related drugs have been investigated for their ability to increase cognition, particularly in demented patients, but these therapies have met with minimal success. Physostigmine and the related synthetic agent neostigmine (eg, Prostigmin ) have been used for the diagnosis and treatment of myasthenia gravis. 3

Dosage

Calabar bean has been widely studied as the pure alkaloid physostigmine. A typical dose for the pure alkaloid is 2 mg. There is no clinical evidence relating to the crude plant material or to an extract.

Pregnancy/Lactation

Documented adverse effects. Avoid use. 3

Interactions

None well documented.

Adverse Reactions

There are few reports on adverse reactions, as calabar bean is toxic to humans.

Toxicology

Physostigmine is extremely toxic, with an oral LD50 of 4.5 mg/kg in mice. The maximum reported number of beans eaten followed by survival of a human is 35. 6 Physostigmine kills by affecting heart contractility and inducing respiratory paralysis.

Bibliography

1. Lewis W, et al. Medical Botany: Plants affecting man's health . New York: John Wiley & Sons, 1977.
2. Osol A, et al. The Dispensatory of the United States of America , 25th ed. Philadelphia: JB Lippincott, 1955:1054.
3. Wickersham RM, Novak KK, managing eds. Drug Facts and Comparisons . St. Louis, MO: Wolters Kluwer Health, Inc.; 2003.
4. Dobelis I. Magic and Medicine of Plants . Pleasantville, NY: Reader's Digest Association, 1986.
5. Evans, W. Trease and Evans' Pharmacognosy . 13th ed. London: Balliere Tindall, 1989.
6. Duke J. Handbook of Medicinal Herbs . Boca Raton, FL: CRC Press, 1985.

Copyright © 2009 Wolters Kluwer Health

More about calabar bean

Hide
(web5)