Astringents are substances that precipitate proteins, but do not penetrate cells, thus affecting the superficial layer only. They toughen the surface making it mechanically stronger and decrease exudation.
ASTRINGENTS
Astringents are
substances that precipitate proteins, but do not penetrate cells, thus
affecting the superficial layer only. They toughen the surface making it
mechanically stronger and decrease exudation. Drugs are:
Tannic
Acid And Tannins
Tannic acid is present in many plants but is generally obtained from
nutgalls of oak. Tannins are found in tea, catechu, nutmeg, areca nut (betel nut),
etc. They denature proteins forming protein tannate. Uses are:
·
Bleeding gums—as glycerine of
tannic acid.
·
Bleeding piles—as tannic acid
suppository.
· Alkaloidal poisoning—precipitates ingested alkaloids as tannates.
(Its use on burns has been abandoned because it forms a crust
under which bacteria could grow. Sufficient systemic absorption often occurred
to cause centrilobular necrosis of the liver.)
Alcohol
Ethanol and methanol are good astringents at 50–90%
concentration. Denatured spirit rubbed on the skin prevents bedsores, but
should not be applied on the sores once these have formed, as it is highly
irritating to raw surfaces. Ethanol is also used as aftershave and on minor
cuts.
Mineral Astringents
Heavy metal ions are astringent and antiseptic.
Alum has been used as aftershave and as local haemostatic on minor cuts. Other
aluminium, zinc and zirconium salts are used as antiperspirants. They diffuse
through the sweat ducts, reduce secretion from glands and partially block the
ducts as well. Their antibacterial action prevents decomposition of sweat by
bacteria, reducing body odor.
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