Rhamnus purshianus Bark Extract

Rhamnus purshianus Bark Extract

Cascara sagrada (Rhamnus Purshiana, U.S.P.) is the dried bark of Rhamnus purshianus, DC. (N.O. Rhamneae), a shrub growing in North California, Oregon, and Washington. It is collected in the spring and early summer, and dried in the shade. It is generally considered that the action of the bark becomes milder and less emetic by keeping; hence matured bark (three years old) is preferred for pharmaceutical purposes. The bark occurs in quilled, channelled, or curved pieces, varying considerably in size, but often about 10 centimetres long, 1 to 2 centimetres wide, and 1 to 2 millimetres thick, thin bark being preferred for use in pharmacy.

The cork is nearly smooth, dark purplish-brown in colour, and bears scattered lenticels, but in most pieces the cork is more or less completely covered by a whitish coat of lichens; the inner surface is of a yellowish-brown or dark brown colour, and faintly striated and corrugated. It breaks with a short fracture, which is somewhat fibrous near the inner surface. The transverse section exhibits a narrow purplish cork, a yellowish-grey cortex, in which groups of sclerenchymatous cells may be distinguished, and a brownish-yellow bast, containing wavy, medullary rays. The odour is characteristic, though not powerful; the taste is nauseous and persistently bitter.

Constituents.—The constituents of the bark are but imperfectly known. It has been proved to contain emodin and an allied substance, possibly identical with the frangula-emodin of alder buckthorn bark; fat (2 per cent.), glucose, and a hydrolytic enzyme have also been found in it, as well as a small quantity of a substance yielding, on treatment with acids, syringic acid. Neither chrysophanic acid nor chrysarobin is present. The assertion has been made that the bark contains glucosides which yield on hydrolysis emodin, chrysophanic acid, etc., but the evidence on this point is conflicting.

The bitter principle is apparently a lactone, which is converted into less bitter salts by treatment with alkalies; upon this property the methods of making tasteless liquid extracts are based, but simultaneous loss of activity occurs. The total amount of oxymethylanthraquinones present in the bark, or extractable after boiling with dilute sulphuric acid, has been estimated to be from 1.4 to 2 per cent., but although these bodies are laxative, this proportion can scarcely influence the activity of the drug. The principal purgative constituent of cascara bark remains, therefore, still unknown. The drug yields about 5 per cent. of ash, and about 27 per cent. of aqueous extractive.
Action and Uses.—Cascara sagrada is a mild laxative. It acts principally on the large intestine and empties the rectum, producing no inflammation. It is suitable for delicate and elderly persons, and is a good laxative in haemorrhoidal conditions; small repeated doses are preferred in habitual constipation. It is administered in the form of liquid extract of cascara in a mixture combined with glycerin, or alkalies, especially aromatic spirit of ammonia; mixtures with mineral acids and salts are often unpresentable in appearance. Elixir Cascarae and Syrupus Cascarae Aromaticus are not unpleasant liquid forms of extract of cascara; for children, the miscible liquid extract may be given with glycerin and syrup, flavoured with liquid extract of liquorice. On account of the unpleasant taste of the liquid extract, it is very frequently given in gelatin capsules, containing the equivalent of 6 to 30 decimils (0.6 to 3.0 milliliters) (10 to 45 minims) of liquid extract in each; they are readily soluble. Tablets contain from 6 to 30 centigrams (1 to 5 grains) of solid extract, and pills are prepared of similar strengths. The latter are best massed with 60 per cent. alcohol, adding a little powdered gum acacia. Extract of cascara is frequently combined with euonymin, nux vomica, aloin, belladonna, or strychnine, in pill or tablet form.
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