Calabar beans, or Ordeal Beans (Physostigma, U.S.P.), are the ripe seeds of Physostigma venenosum, Balfour (N.O. Leguminosae), a climbing plant indigenous to the West Coast of Africa. The beans are dark chocolate brown in colour, and reniform. in shape, about 25 millimetres long, 18 millimetres broad, and 12 millimetres thick, with a deep groove (the hilum) extending almost the length of the arched side. The surface is somewhat rough, but with a slight polish. Cut transversely the beans exhibit a thick, brown shell, surrounding two large, firm, white, starchy cotyledons, which enclose a large cavity, the air in which causes the entire seeds to float upon water. The odour and taste are not specially characteristic. The seeds of Entada scandens (Garbee beans), of Mucuna urens (horse-eye beans), and of Pentaclethra macrophylla have been offered as Calabar beans; they bear scarcely any resemblance to the genuine. A seed very similar in appearance to Calabar beans, but nearly cylindrical in shape and with a shorter hilum, has also been imported; the plant yielding it, which is unknown, has been named Physostigma cylindrospermum, Holmes;it is said to contain eserine.
Constituents.—The chief constituent of Calabar beans is the alkaloid physostigmine (eserine), with which are associated small quantities of eseridine and eseramine. Physostigmine forms large crystals melting at 105° to 106°; it is tasteless, laevorotatory, sparingly soluble in water, readily in alcohol, ether, chloroform, benzene, or carbon bisulphide. Its characteristic reactions are described under Physostigminae Sulphas. Eseridine is crystalline, and changes, on heating with a mineral acid, into physostigmine; it has but little action on the pupil of the eye, and is not employed medicinally. Eseramine crystallises in needles, melting at 238° to 240°. The presence of calabarine, which was formerly considered to be a constituent of the seeds, has not been confirmed. The total alkaloid varies from 0.15 to 0.3 per cent. (U.S.P., not less than 0.15). The seeds also contain the phytosterol stigmasterol, and abundance of starch; and yield about 4 per cent. of ash.
Action and Uses.—The properties of Calabar beans are virtually those of the alkaloid physostigmine (see Physostigminae Sulphas). An extract and a tincture are prepared from the crude drug. They are employed in tetanus, in hemiplegia and paraplegia, in locomotor ataxy, and in strychnine poisoning. The extract may be administered in pills or cachets, or as a solution prepared for hypodermic use by dissolving it in water and filtering. In cases of poisoning by Calabar beans, the stomach should be evacuated, and atropine injected until the pulse quickens or the symptoms pass off.
Dose.—3 to 10 centigrams to 1 1/2 grains).
- Extractum Physostigmatis, B.P.—EXTRACT OF CALABAR BEAN.
- Calabar bean, in No. 40 powder, 100; alcohol (90 per cent.), 500; milk sugar, in fine powder, a sufficient quantity. Macerate the drug for forty-eight hours, with 125 of the alcohol, then percolate with the remainder of the alcohol, press the marc, filter, recover most of the alcohol by distillation, evaporate to a very soft extract, and add three times its weight of milk sugar. Dose.—15 to 60 milligrams (1/4 to 1 grain).
- Extractum Physostigmatis, U.S.P.—EXTRACT OF PHYSOSTIGMA.
- Physostigma, in No. 80 powder, 100; alcohol (95 per cent.), and peeled Russian glycyrrhiza, in No. 80 powder, a sufficient quantity. The physostigma is exhausted with the alcohol, the product evaporated to dryness, and sufficient glycyrrhiza added to make the extract contain 2 per cent. of ether-soluble alkaloids. Average dose.—8 milligrams (4 grain).
- Tinctura Physostigmatis, B.P.C.—TINCTURE OF CALABAR BEAN. Syn.—Tincture of Physostigma. 1 in 5.
- Used in paralysis and other nervous diseases, apparently for the exciting action of the drug on motor nerve-endings. Dose.—3 to 10 decimils (0.3 to 1.0 milliliters) (5 to 15 minims).
- Tinctura Physostigmatis, U.S.P.—TINCTURE OF PHYSOSTIGMA.
- Prepared by extracting 10 of Calabar bean with sufficient 95 per cent. alcohol to produce 100, and should contain 0.014 per cent. w/v of alkaloids. Average dose.—1 mil (15 minims).
The British Pharmaceutical Codex, 1911, was published by direction of the Council of the Pharmaceutical Society of Great Britain.