Rhubarb root (Rhei radix)

Published November 1, 1984; Revised December 5, 1984; Replaced July 21, 1993.
List of German Commission E Monographs (Phytotherapy)

Rhabarber

Name of Drug

Rhei radix, rhubarb root.

Composition of Drug

Rhubarb consists of the dried under-ground parts of Rheum palmatum L., R. officinale Baillon or of both species [Fam. Polygonaceae], as well as their preparations in effective dosage. Stem parts, roots and most of the bark are removed from the rhizomes.

The bark contains anthranoids, mainly of the rhein and physcion type.

The drug must conform to currently valid pharmacopeia.

Pharmacological Properties, Pharmacokinetics, Toxicology

1,8-dihydroxy-anthracene derivatives have a laxative effect. This effect is primarily due to the influence of the herb on the motility of the colon, inhibiting stationary and stimulating propulsive contractions. This results in an accelerated intestinal passage and, because of the shortened contact time, a reduction in liquid absorption. In addition, stimulation of the active chloride secretion increases the water and electrolyte content of stool.

Systematic studies pertaining to the kinetics of rhubarb preparations are not available; however, it must be supposed that the aglycones contained in the drug are already absorbed in the upper small intestine. The ß-glycosides are prodrugs which are neither absorbed nor cleaved in the upper gastrointestinal tract. They are degraded in the colon by bacterial enzymes to anthrones. Anthrones are the laxative metabolites.

Active metabolites of other anthronoids, such as rhein, infiltrate in small amounts into the milk ducts. A laxative effect on nursing infants has not been observed. The placental permeability for rhein is very small.

Drug preparations [i.e., herbal stimulant laxative drugs] have a higher general toxicity than the pure glycosides, presumably due to the content of aglycones.

Experiments pertaining to the genotoxicity of rhubarb and its preparations are not available. Some positive data were obtained for aloe-emodin, emodin, physcion and chrysophanol. No data are available for carcinogenicity.

Clinical Data 1. Uses Constipation.

2. Contraindications

Intestinal obstruction, acute intestinal inflammation, e.g., Crohn's disease, colitis ulcerosa, appendicitis, abdominal pain of unknown origin. Children under 12 years of age; pregnancy.

3. Side Effects

In single incidents, cramp-like discomforts of the gastrointestinal tract. These cases require a dosage reduction.

With chronic use or abuse:

Disturbances of electrolyte balance, especially potassium deficiency, albuminuria, and hematuria. Pigment implantation into the intestinal mucosa (pseudomelanosis coli) is harmless and usually reverses upon discontinuation of the drug. Potassium deficiency can lead to disorders of heart function and muscular weakness, especially with concurrent use of cardiac glycosides, diuretics, or corticoadrenal steroids. 4. Special Caution for Use Stimulating laxatives must not be used over an extended period (1 - 2 weeks) without medical advice.

5. Use During Pregnancy and Lactation

Because of insufficient toxicological investigation, this drug should not be used during pregnancy and lactation.

6. Interactions with Other Drugs

With long-term use/abuse, due to loss in potassium, an increase in effectiveness of cardiac glycosides and an effect on antiarrhythmics is possible. Potassium deficiency can be increased by simultaneous application of thiazide diuretics, corticoadrenal steroids or licorice root.

7. Dosage and Administration

Cut bark, powder or dry extracts for teas, decoction, cold maceration or elixir.

Liquid or solid forms of medication exclusively for oral use.

Unless otherwise prescribed:

20 - 30 mg hydroxyanthracene derivatives/day, calculated as rhein. The individually correct dosage is the smallest dosage necessary to maintain a soft stool.

Note: The form of administration should be smaller than the normal daily dosage. Rhubarb preparations rich in tannin and deficient in anthranoids can have a constipating effect.

8. Overdosage

Electrolyte and fluid imbalance.

9. Special Warnings

Use of a stimulating laxative for longer than the recommended short-term application can cause an increase in intestinal sluggishness.

The preparation should be used only if there are no results from a change of diet or usage of bulk-forming products.

10. Effects on Operators of Vehicles and Machinery

None known.