Frangula, or alder buckthorn bark (Frangula, U.S.P.), is obtained from the stem and branches of Rhamnus Frangula, Linn. (N.O. Rhamneae), a shrub widely distributed over Europe. The dried bark should mature for at least a year before being employed medicinally. The bark varies considerably in appearance, according to the age of the branch or stem from which it has been taken. Young bark, which is to be preferred, occurs in narrow (about 1 centimetre), single or double quills, and is of papery texture. It is covered with smooth cork of a dark purplish colour, and bears numerous whitish lenticels; when gently scraped the inner layers are seen to be crimson in colour. The inner surface of the bark is brown and very finely striated. The fracture is short in the cork and cortex, but fibrous in the bast. Older bark is rougher externally, thicker, and usually in single quills or channelled pieces. Transverse sections are characterised by the absence of sclerenchymatous cells from the cortex and bast. The taste of the drug is sweetish and slightly bitter. Frangula or alder buckthorn should be distinguished from common buckthorn (Rhamnus catharticus, Linn.., from the ripe berries of which Syrupus Rhamni is prepared.
Constituents.—The constituents of frangula bark, especially those to which the laxative properties are due, are but imperfectly known. A yellow, crystalline glucoside, frangulin, yielding by hydrolysis rhamnose (isodulcite) and frangula-emodin (trioxymethylanthraquinone), has been isolated from it. The emetic action of the fresh bark has been attributed to an enzyme, and it has been asserted that the maturing of the bark can be rendered unnecessary by heating it for a short time to 100°, thus rendering the enzyme inactive. Possibly other glucosides, yielding oxymethylanthraquinones by hydrolysis, are also present, and contribute to the laxative action of the drug, but the evidence in favour of this assumption is not conclusive. Frangula-emodin appears to be identical with the emodin of rhubarb, but not with that of aloes or senna.
Action and Uses.—Frangula bark has properties similar to those of cascara sagrada. It is used as a mild purgative, principally in the form of fluidextract.
- Fluidextractum Frangulae, U.S.P.—FLUIDEXTRACT OF FRANGULA.
- Frangula, in No. 40 powder, 100 alcohol (95 per cent.) and water, of each a sufficient quantity, to 100. Prepared by percolation with a menstruum of the alcohol, 5, and distilled water, 8. 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.