Plants> <Rhizoma Rhei>
Rhizoma Rhei consists of the underground parts (rhizome and root) of Rheum
officinale Baill., or R. palmatum L, (Polygonaceae).
Selected vernacular names
Akar kalembak, Chinese rhubarb, chuong diep dai hoilng, dai hoilng, daioh,
aiou, kot nam tao, rawind, Rhabarberwurzel, rhabarbarum, rhubarb, rhubard
de Chine, rhubarb root, turkey rhubarb, ta-huang.
Rheum species are perennial herbs resembling the common garden rhubarb
except for their lower growth and shape of their leaf blades; the underground
portion consists of a strong vertical rhizome with fleshy, spreading roots;
the portion above ground consists of a number of long petioled leaves
that arise from the rhizome in the spring, and flower shoots bearing elongated
leafy panicles that are crowded with greenish white, white, to dark purple
flowers; the lamina is cordate to somewhat orbicular, entire or coarsely
dentate (Rheum offinale) or palmately lobed (R. palmatum). The fruit
is an ovoid-oblong or orbicular achene bearing 3 broad membranous wings
and the remains of the perianth at the base.
material of interest: rhizomes and roots
appearance of the rhizomes and roots varies according to the plant's geographical
origin. They occur on the market in sub cylindrical. barrel-shaped, plano-convex
or irregularly formed pieces. frequently showing a perforation, or in
cubes or rectangular pieces, the last-commonly known as "rhubarb
fingers". They are hard and moderately heavy. The outer surfaces
are smooth, longitudinally wrinkled or sunken, yellowish brown and mottled
with alternating striae of greyish whitc parenchyma and brownish or reddish
medullary ray.s, while here and there may be secn brown cork patches and
branched scars, "star spots", of leaf trace fibrovascular bundles.The
fracture is uneven and granular, the fractured surface pinkish brown.
The smooth transverse surface of the rhizome exhibits a cambium line near
the periphery traversed by radial lines that represent medullary rays
that project for a short distance. within it. The large area within this
circle of medullary rays contains stellate vascular bundles 2-4 mm in
diameter that are arranged in a more or less continuous circle in R. palmatum
or scattcrcd irregularly in R. officinale.
Odour, characteristic aromatic; taste, slightly astringent and bitter;
when chewed, gritty bctwcen thc tecth; colour, yellow-brown to light brown.
The transverse section of the rhizome shows wavy medullary rays, 2-4 cells
in width; the xylem consists of a matrix of wood parenchyma and resembles
the phloem and cortex regions in that the cells possess either starch,
tannin, or large cluster crystals of calcium oxalate. Large, reticulately
thickened vessels occur singly or in small groups. Embedded in the parenchyma
near the cambium line and mostly in the pith are a number of compound
("stellate") fibrovascular bundles, each of which consists of
a small circle of open collateral bundles separated from each other by
yellowish brown medullary rays containing anti raquinone derivatives.
The bundles differ from the ordinary open collateral bundle in showing
phloem inside and xylem outside the cambium. In R. officinale the compound
bundles ("stellate spots") are scattered through the pith, whereas
in R. palmatum they are mostly arranged in a ring, the remainder being
scattered on either side of the ring.
Powdered Rhizoma Rhei is dusky yellowish orange to moderate yellowish
brown, and coloured red in the presence of alkali. Under the microscope,
it shows numerous starch grains, spherical, single or 2-4-compound, 1-25
um in diameter; fragments of non-lignified, reticulate and spiral tracheae,
vessels, parenchyma cells containing starch grains or tannin masses; large
rosette aggregates of calcium oxalate, 30-60um, frequently over 100um,
and occasionally attaining a diameter of 190 um and medullary-ray cells
containing an amorphous yellow substance, insoluble in alcohol but soluble
in ammonia test solution with a reddish or pink colour; cork, sclerenchymatous
cells, and fibres absent.
Rheum officinale and R. palmatum are cultivated in China (Gansu, Sichuan.
and Oinghai provinces), the Democratic People's Republic of Korea and
the Republic of Korea. There are several commercial grades (rhizomr with
or without rootlets, peeled or unreeled. in transverse or longitudinal
Macroscopic and microscopic examinations: microchemical colour tests and
thin-layer chromatographic analysis for the presence of anthraquinones.
The test for Salmonella spp. in Rhizoma Rhei products shoul dbe negative.
The maximum acceptable limits of other microorganisms are as follows.
For preparation of decoction: aerobic bacteria--not more thatn 10 4/g:
fungi--not more than 10 5/g; Escherichia coli--not more than 10 2/g.
Preparations for internal use: aerobic bacteria--not more than 10 5/g
or ml: fungi--not more than 10 4/g or ml; enterobacteria and certain Gram-negative
bacteria--not more than 10 3/g or ml: Esscherichia coli--o/g or ml.
Foreign Organic Matter
Not more than 1.0%
Not more than 12% (2, 3).
Not more than 2.0%.
Not less than 30%.
Not more than l2%.
To be established in accordance with national requirements. Normally,
the maximum residue limit of aldrin and dieldrin in Rhizoma Rhei is not
more than 0.05 mg/kg. For other pesticides, see WHO guidelines on quality
control methods for medicinal plants and guidelines for predicting dietary
intake of pesticide residues.
Recommended lead an dcadmium levels are no more than 10 and 0.3mg/kg,
respectively, in the final dosage form of the plant material.
For analysis of strontium-90, iodine-131, caesium-134, caesium-137, and
plutonium-239, see WHO guidelincs on quality control methods for
Other purity tests
Chemical and water-soluble extractive tests to be established in accordance
with national requirements.
Contains not less than 2.2% hydroxyanthracene derivatives calculated as
rhein. Quantittive analysis of total hydroxyanthracene glycosides,calculated
as rhein, perofrmed by spectophotometric analysis. High-performance
liquid chromatography is also vailable for quantitative analysis hydroxyanthracene
derivatives calculated as rhein.
chromatography is employed for the qualitative analysis for he presence
of emodin, physcione (emodin 3-methyl ether), chrysophanol (chrysophanic
acid), rhein, and aloe-emodin.
The major constituents arc hydroxyanthracene derivatives (2-5%) including
emodin, physcione, aloe-emodin, and chrysophanol glycosides, along with
di-O, C-glucosides of the monomeric reduced forms (rheinosides A-D), and
dimeric reduced forms (sennosides A-F). The level of the oxidized forms
is maximal in the summer and almost nil in the winter. Until the 1950s,
chrysophanol and other anthraquinones were considered to be the constituents
producing the purgative action of rhubarb. Current evidence indicates
that the major active principles are the dimeric sennosides A-F.
Dried plant material and preparations standardized to contain 10-30 mg
of hydroxyanthracene derivatives per dose.. Package in well-closed, light-resistant
Uses supported by clinical data
Short-term treatment of occasional constipation.
described in pharmacopoeias and in traditonal systems of medicine
described in folk medicine, not supported by eperimental or clinical data
To treat hypotension, increase peripheral vasodilation, and inhibit blood
As shown for senna, the mechanism of action is twofold: (1) stimulation
of colonic motility, which augments propulsion and accelerates colonic
transit (which in turn reduces fluid absorption from the faecal mass);
and (2) an increase in the paracellular permeability across the colonic
mucosa probably owing to an inhibition of Na + /K+ .-exchanging ATPase
or to an inhibition of chloride channels which results in an increase
in the water content in the large intestine. Purgation is followed by
an astringent effect owing to the tannins present.
The active constituents of Rhizoma Rhei are the anthraquinone glycosides,
sennosides A-F and rheinosides A-D. The rheinosides are similar to aloin
A and B, the main cathartic principles of aloe. The cathartic action of
both the sennosides and rheinosides is limited to the large intestine,
where they directly increase motor activity in the intestinal tract. Consequently,
they are seldom effective before 6 hours after oral administration, and
they sometimes do not act before 24 hours.
mechanism of action is similar to that of other anthraquinone stimulant
laxatives. Both the sennosides and rheinosides are hydrolysed by intestinal
bacteria and then reduced to the active anthrone metabolite, which acts
as a stimulant and irritant to the gastrointestinal tract. Preparations
of rhubarb, are suitable as an occasional aperient, but should not be
used in chronic constipation. A variable amount is absorbed and imparts
a yellowish brown colour to the urine, which is changed toa purplish red
on the addition of alkali. Rhizoma Rhei preparations have becn emrloyed
occasionally for their astrinent after effects, to check the diarrhoea
produced by irritating substances in the intestines.
The major symptoms of overdose are griping and severe diarrhoea with consequent
losses of fluid and electrolytes. rreatment should be supportive
with generous amounts of fluid. Electrolytes, particularly potassium should
be monitored, especially in children and the elderly.
As with other stimulant laxatives, products containing Rhizoma Rhei should
not be administered to patients with intestinal obstruction and stenosis,
atony, severe dehydration states with water and electrolyte depletion,
or chronic constipation. Rhizoma Rhei should not be used in patients
with inflammatory intestinal diseases, such as appendicitis, Crohn disease,
ulcerative colitis, or irritable bowel syndrome, or in children under
10 years of age. Rhizoma Rehi should not be used during pregnancy
or lactation except under medical supervision after respective benefits
and risks have been cosnidered. As with other stimulant laxatives,
Rhizoma Rhei is contraindicated in patients with cramps, colic, haemorrhoids,
nephritis, or any undiagnosed abdominal symptoms such as pain , nausea,
Products containing Rhizoma Rhei should be used only if no effect can
be obtained through a change of diet or use of bulk-forming laxatives.
Stimulant laxatives should not be used when abdominal pain, nausea. or
vomiting are present. Rectal bleeding or failure to have a bowel movement
after the use of a laxative may indicate a seriolls condition. Use of
stimulant laxatives for longer than the recommended short-term application
may increasc intestillal sluggishness.
use of stimulant laxatives for more than 2 weeks requires medical supervision.
use may lead to pseudomelanosis coli (harmless) and to an aggravation
of constipation with dependence and possible need for increased dosages
abuse with diarrhoea and consequent fluid and electrolyte losses (mainly
hypokalaemia) may cause albuminuria and haematuria, and it may result
in cardiac and neuromilscufar dysfunction. the latter particularly in
case of concomitant use of cardiac glycosides (digoxin), diuretics, corticosteroids.
or liquorice root (see below precautions).
Laxatives containing anthraquinone gylcosides hould not be used for periods
longer than 1-2 weeks continually, owing to the danger of electrolyte
Decreased intestinal transit time may reduce absorption of orally administered
imbalances such as increased loss of potassium may potentiate the effects
of cardiotonic glycosides (digitalis, strophanthus). Existing hypokalaemia
resulting from long-term laxative abuse can also potentiate the effects
of antiarrhythmic drugs, such as qunidine, which affect potassium channels
to change sinus rhythm. Simultaneous use with other drugs or herbs
which induce hypokalaemia, such as thiazide diuretics, adrenocorticosteroids,
or liquorice root, may exacerbate electrolyte imbalance.
and laboratory teest interactions
Anthranoid metabolites may not be detectable with standard methods.
Thus results of measuring faecal excretion may not be reliable.
Urinary excretion of certain anthranoid metabolites may discolour the
urine, which is not clincally relevant but may cause false positive results
for urinary urobilinogen and for estrogens when measured by the Kober
mutagenesis, impairment of fertility
Data on the carcinogenicity of Rhzoma Rhei are not available. While
chronic abuse of anthranoid-containing laxatives was hypothesized to play
a role in colorectal cancer, no causal relationship between anthranoid
laxative abuse and colorectal cancer has been demonstrated.
The teratogenic effects of Rhizoma Rhei have not been evaluated.
Products containing Rhizoma Rhei should not be used by pregnant women
because they have a pronounced action on the large intestine and have
not undergone sufficient toxicological investigation.
Anthranoid metabolites appear in breast milk. Rhizoma Rhei should
not be used during lactation as there are insufficient data available
to assess the potential for pharmacological effects in the breast-fed
Use of Rhizoma Rhei for children under 10 years of age is contraindicated.
Single doses may cause cramp-like discomfort of the gastointestinal tract,
which may require a reduction of dosage. Overdoses can lead to colicky
abdominal spasms and pain and the formation f thin, watery stools.
abuse of anthraquinone stimulant laxatives can lead to hepatitis.
Long-term laxative abuse may lead to electrolyte disturbances (hypokalaemia,
hypocalcaemia), metabolic acidosis, malabsorption, weight loss, albuminuria,
and haematuria. Weakness and orthostatic hypotension may be exacerbated
in elderly patients when stimulant laxatives are repeatedly used.
Secondary aldosteronism may occur due to renal tubular damage after aggravated
use. Steatorrhea and protein-losing gastroenteropathy with hypoalbuminaemia
have also been reproted in laxative abuse. Melanotic pigmentation
of the colonic mucosa (pseudomelanosis coli) has been observed in individuals
taking anthraquinone laxatives for extended time periods. The pigmentation
is clinically harmless and usually reversible within 4-12 months after
the drug has been discontinued. Conflicting data exist on
other toxic effects such as iintestinal-neuronal damage after long-term
The individually correct dosage is the smallest dosage necessary to maintain
a soft stool. The average dose is 0.5-1.5g of dried plant material or
in decoction; preparations standardized to contain 10-30mg of hydroxyanthracene
derivatives, usually taken at bedtime.
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