Rhubarb

RHUBARB (Pharmacopoeia VII), Rheum palmatum L. var. tanguticum Maximowicz, of the buckwheat family (Polygonaceae). A perennial herbaceous plant with very large basal leaves. It grows wild in southern Mongolia, Tibet, and China (see Medicinal Plants). It is cultivated in Germany; in the USSR, cultivation has been introduced, but it does not yet have industrial significance. Rheum officinale Baill. (see figure) yields a poorer variety of rhubarb. Harvesting is carried out in the autumn; the roots are discarded, and the rhizomes are cleaned and cut into pieces. According to the German Pharmacopoeia (1926), the roots are also used. Commercial rhubarb consists of pieces of various shapes; their surface is uniformly yellow, and the fracture is marbled; scattered across a white background are a multitude of orange dots and lines (medullary rays containing orange-colored anthraglycosides), which in places form the "star" figures characteristic of the rhizome of true rhubarb (leaf bundles in cross-section). The odor of rhubarb is peculiar, the taste is bitter-astringent; rhubarb stains saliva yellow (anthraglycosides); it crunches between the teeth due to the abundance of large druses of calcium oxalate salt. Rhubarb can be stored for years without losing its potency, but it spoils in a damp room, easily absorbing moisture and becoming moldy. Rhubarb contains two groups of substances that determine its medicinal properties: anthraglycosides and tannoglycosides. Anthraglycosides are found in both bound and free states; upon cleavage, they yield aglycones: rheum-emodin [C₁₄H₄O₂(CH₃)(OH)₃ - methyltrioxyanthraquinone], identical to frangula-emodin (see Buckthorn), chrysophanic acid [(HO)(CH₃)-C₆H₂C₆H₃OH, methyldioxyanthraquinone], rhein [C₁₄H₆O₂(CH₃)(OH)₄ - tetraoxymethylanthraquinone], and a number of other closely related compounds. These are orange-colored substances, easily soluble in water, even more so in alkalis, and less so in alcohol. Tannoglycosides are less soluble

in water and in alkalis, but are well soluble in alcohol. The Bornträger qualitative reaction (see Buckthorn) is used for the identification of rhubarb. Various chemical methods have been proposed for the quantitative determination of anthraglycosides. The biological action of rhubarb is tested on white mice. Rhubarb belongs to the group of plant laxatives that act on the large intestine similarly to buckthorn, aloes, and senna. In large doses, rhubarb causes liquid stools; in medium doses, mushy stools; and in small doses, it slows peristalsis and is therefore used against diarrhea in children. If the dose of rhubarb is significant (0.8–1.0 g or more), then the influence of anthraglycosides—both free and, perhaps even more so, those not isolated in pure form and close to cathartic acid—is felt first and most strongly in humans. The action of rhubarb, as it contains anthracene derivatives, is caused primarily by the stimulation of the muscles of the large intestine; substances of the anthracene group have only a weak effect in the small intestine, probably due to the absence of appropriate conditions for their dissolution there. It is noted that the presence of bile in the intestine is a necessary condition for the laxative effect of rhubarb. With large doses of rhubarb, or when its contents are evacuated from the intestine sufficiently quickly, the rhubarb-tannin substances usually do not have time to exert their astringent effect; however, sometimes the laxative effect of rhubarb is subsequently replaced by constipation, which is associated with the strong influence of tannoglycosides. Emodin, chrysophan, as well as amorphous components of rhubarb that have not yet been sufficiently studied chemically—rhaporetin, pheoretin, and erythroretin—possess antiseptic properties, as a result of which the therapeutic value of rhubarb increases significantly compared to other laxatives that do not have antiseptic properties. Large doses of rhubarb, while exerting a laxative effect, can cause pain and cramping in the intestine, especially if the medicine is taken on an empty stomach. Medium doses of rhubarb (0.1–0.2 g per dose) cause mushy stools (laxative effect) as a result of the mild irritating effect of anthraglycosides on the intestine, which is also moderated by the influence of tannoglycosides or rhubarb-tannin substances, which manifest their effect in these cases due to the longer duration of rhubarb's stay in the intestines. If rhubarb is given in small doses (0.05–0.1 g), then the rhubarb-tannin substances, through their astringent action, cause the cessation of diarrhea, in which the components of rhubarb belonging to the anthracene series play a significant role by acting antiseptically. When taking rhubarb, thanks to the excreted anthraquinone derivatives, urine, feces, sweat, and milk take on a yellow color, which turns red under the influence of alkalis. Rhubarb is prescribed in powders, pills, and infusions at 0.8–2.0 g as a laxative and at 0.1–0.2 g as a regulator of intestinal function. Preparations: Pulvis Magnesiae cum Rheo (Pharmacopoeia VII), children's powder, consists, in addition to rhubarb, of magnesium carbonate, which neutralizes acids and acts as a laxative, and sugar with essential dill oil, which acts as a carminative. It is prescribed for children from a pinch to a teaspoon, depending on age and indications. Extractum Rhei (Pharmacopoeia VII), dry rhubarb extract; prescribed internally in pills at 0.1–0.3 g as a tonic; at 0.5–1.0 g as a laxative. Extractum Rhei compositum (Pharmacopoeia VII), compound rhubarb extract, in pills at 0.1–0.3 g as a tonic; at 0.5–1.0 g as a strong laxative. Sirupus Rhei (Pharmacopoeia VII), rhubarb syrup, taken by the teaspoon as a gentle laxative for children. Tinctura Rhei aquosa (Pharmacopoeia VII), aqueous tincture of rhubarb, used as a laxative by the tablespoon. Tinctura Rhei amara spirituosa (Pharmacopoeia VII), bitter alcoholic tincture of rhubarb, used in doses of 1/2–1 teaspoon 2–3 times a day 1/2 hour before meals as a stomachic.