Astringents

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.