Kaolin

• BPHeavy Kaolin
• JPKaolin
• Ph. Eur.Kaolin, Heavy
• USP–NFKaolin

Argilla; bolus alba; China clay; hydrated aluminium silicate; porcelain clay; white bole; heavy kaolin; light kaolin

Hydrated aluminium silicate · [1332-58-7]

Al2H4O9Si2 (Al2O3·2SiO2·2H2O) · 258.16

Adsorbent, Diluent (filler)

Typical concentrations: — · Dosage forms: Solid, Liquid

Used in oral solid dosage forms as a diluent and adsorbent, and in topical products such as dusting powders, poultices and face masks. As an active substance it has been used as an oral adsorbent in antidiarrhoeal mixtures. It is also widely used in cosmetics and as a filler in many industries.

A white or greyish-white, unctuous, fine powder that is practically odourless and has an earthy taste. It is a purified natural clay consisting mainly of the mineral kaolinite; light kaolin contains a dispersing agent and is finer than heavy kaolin.

Density

true density about 2.6 g/cm³

Solubility

practically insoluble in water, ethanol, ether, other organic solvents, cold dilute acids and alkali hydroxide solutions

Structure

layered (1:1) aluminosilicate; swells very little in water

Heat stability

withstands dry-heat sterilisation; loses structural water only at several hundred °C

Stable. Store in a well-closed container in a cool, dry place. Because it may carry bacterial spores, including those of Clostridium species, kaolin for poultices and dusting powders should be sterilised, for example by dry heat.

Kaolin adsorbs many drugs and can reduce their oral absorption when taken at the same time; reduced absorption has been reported, for example, with digoxin, lincomycin and tetracyclines. It can also adsorb preservatives and reduce their activity.

Mined natural clay is purified by suspending it in water and separating the fine fraction from sand, mica and other impurities by sedimentation or elutriation; it is then bleached if necessary, dried and milled.

Not absorbed orally and regarded as non-toxic by mouth. Chronic inhalation of kaolin dust in occupational settings can cause pneumoconiosis (kaolinosis).

Observe normal precautions for the quantity handled. Avoid generating dust; use local exhaust, eye protection and a dust respirator.

Included in the FDA Inactive Ingredient Database (oral capsules and tablets; topical preparations) and in non-parenteral medicines licensed in Europe.

Bentonite; magnesium aluminium silicate; talc; light kaolin.

Pharmacopoeial kaolin is tested for limits on soluble impurities, heavy metals and swelling, and grades for topical or oral use should be checked for microbial quality. Separating the doses of kaolin-containing products and other oral drugs by at least two hours reduces adsorption interactions.