Bentonite

• BPBentonite
• JPBentonite
• Ph. Eur.Bentonite
• USP–NFBentonite

Bentonitum; mineral soap; montmorillonite clay; soap clay; taylorite; wilkinite

Bentonite (native colloidal hydrated aluminium silicate, mainly montmorillonite) · [1302-78-9]

Al2O3·4SiO2·H2O (idealised)

Gelling agent, viscosity modifier, Adsorbent

Typical concentrations: — · Dosage forms: Liquid, Semi-solid

Used as a suspending agent and viscosity builder in oral and topical suspensions, lotions and creams, as an emulsion stabiliser, and as an adsorbent and clarifying agent. Typical concentrations: suspending agent 0.5–5%; emulsion stabiliser about 1%; adsorbent and clarifying agent variable.

A very fine, odourless, pale buff or cream to greyish-white powder, free from grit, with a slightly earthy taste. It consists of particles about 50–150 µm along with numerous particles of colloidal size, and its plate-like montmorillonite layers carry exchangeable cations, usually sodium or calcium.

pH

9.5–10.5 (2% w/v aqueous suspension)

Loss on drying

about 5–8% w/w

Swelling

swells markedly in water, up to about 12 times its dry volume, forming thixotropic dispersions and, at higher concentrations, gels

Solubility

practically insoluble in water, ethanol and other organic solvents

Hygroscopic. Store in an airtight container in a cool, dry place. Aqueous suspensions are fairly stable and can be sterilised by autoclaving; they support microbial growth, so a preservative is needed.

Aqueous dispersions are flocculated and lose viscosity in the presence of electrolytes and acids, and are most stable above about pH 6. The negatively charged clay adsorbs cationic drugs and preservatives (for example quaternary ammonium compounds), which can reduce their activity or availability.

Mined from natural deposits formed by weathering of volcanic ash, then dried, milled and sieved; it may be purified or treated to adjust the exchangeable cation content.

Not absorbed after oral administration and regarded as non-toxic and non-irritant in oral and topical use. It must not be given parenterally. Prolonged inhalation of the dust should be avoided because of possible crystalline silica content.

Observe normal precautions for the quantity handled. Use eye protection and a dust mask, and avoid creating dust.

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

Attapulgite; kaolin; magnesium aluminium silicate; purified bentonite; hectorite.

Bentonite hydrates best when sprinkled onto the surface of water and left to stand, or when dispersed with high-shear mixing; adding water to the powder tends to form lumps. Pre-wetting with glycerol also helps dispersion.