Page 241 - Pharmacognosy 2 PG303

Pharmacognosy-2 (PG303) Level 2 Clinical Pharmacy-Pharm D

The amount of drug taken has to be raised in order, to achieve the same effect.
Use is also made of the laxative action in liver and biliary disorders, which are
not infrequently accompanied by constipation; hence, the drug and drug extracts
are accompanied of many cholagogues.
On the other hand, use as an astringent, eg. as anti-diarrhea, has greatly
decreased. Because of the bitter taste of the anthracene glycosides, small
amount of rhubarb are used, e.g. in the form of alcohol extracts (Tinctura Rhei
vinosa) as a stomachic.
It is known that one of the components of the tannin mixture (galloyl-
dihydro-cinnamoyl-glucose) has an analgesic and anti-inflammatory actions
which are comparable with those of phenyl-butazone and acetyl salicylic acid,
respectively. The stilbene glucosides are moderately active as α-glucosidase
inhibitors.

Side Effects
If used as prescribed, none was known. Like all anthracene glycoside-
containing drugs, rhubarb should not be used continuously over for a prolonged
period since this disturbs the water and electrolyte balance. Rhubarb should
not be taken during pregnancy (reflex stimulation of uterus) or during
lactation (a proportion of the aglycones reaches the mother's milk) or in cases
of intestinal obstruction (danger of intestinal rupture).

Anthraquinones are partly conjugated with glucuronic and sulfuric acids
and are excreted in the urine, which then takes on a deep yellowish-brown color
and which on being made alkaline becomes red to reddish brown.

Adulteration
It is observed now and then, especially with Rheum rhaponticum L.
(rhapontic), but also with R rharbarbarum L. and other Rheum species; they
all contain a much smaller amount of anthracene derivatives than does the
pharmaceutical drug. The detection is based on the occurrence of stilbene
derivatives, especially rhaponticin (= rhapoticoside). Rhapontic rhubarb is
identified as follows:
I- Examine powdered rhubarb with the aid of a lens in UV light, a velvet reddish
brown fluorescence appears, but no shining bluish violet spots or particles.
2- Place on a microscope slide 2-3 drops of freshly prepared 10% solution of
furfural in alcohol (90%) and 3 drops of sulfuric acid, then sprinkle a little
powdered rhubarb, and immediately observe under the microscope, no violet
color is produced.

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