Bentonite

Category

Adsorbent; Suspending Agents; Thickener; Dairy Stabilizer; Stabilizer

Molecular Formula

Al2O3`4SiO2`H2O

Molecular Weight

359.16

Grade

Pharmceutical Excipients

Description

Bentonite is a crystalline, claylike mineral, and is available as an odorless, pale buff, or cream to grayish-colored fine powder, which is free from grit. It consists of particles about 50-150 mm in size along with numerous particles about 1-2 mm. Microscopic examination of samples stained with alcoholic methylene blue solution reveals strongly stained blue particles. Bentonite may have a slight earthy taste.

UNII

A3N5ZCN45C

Chemical Name

Bentonite

CAS Number

1302-78-9

Synonyms

Albagel; bentonitum; E558; mineral soap; Polargel; soap clay; taylorite; Veegum HS; wilkinite

Administration route

Dental; Oral; Topical; Transdermal

Dosage Form

Oral capsules, tablets, and suspensions, topical suspensions, controlled-release transdermal films, and pessaries

Stability and Storage Conditions

Bentonite is hygroscopic and should avoid absorbing moisture from the environment. The bentonite aqueous suspension can be sterilized by autoclaving. After the solid bentonite was dried at 100°C, it was kept at 170°C for 1 hour for dry heat sterilization. This product should be sealed and stored in a cool, dry place.

Commonly used amount and the maximum amount

Concentration: Adsorbent (clarifying agent) 1.0-2.0%; Emulsion stabilizer 1.0%; Suspending agent 0.5-5.0%.

Source and Preparation

Bentonite is a non-metallic mineral with montmorillonite as the main mineral component. The montmorillonite structure is a 2:1 crystal structure composed of two silicon-oxygen tetrahedra sandwiching a layer of aluminum-oxygen octahedron. Due to the formation of montmorillonite unit cells There are some cations in the layered structure, such as Cu, Mg, Na, K, etc., and the interaction between these cations and the montmorillonite unit cell is very unstable, and they are easily exchanged by other cations, so they have good ion exchange properties. People call it "universal soil". It is a colloidal natural hydrated aluminum silicate colloid produced in Canada and the United States. The natural ore must remove slag and inswellables before it is suitable for pharmaceutical applications.

Applications

Bentonite is a naturally occurring hydrated aluminum silicate used primarily in the formulation of suspensions, gels, and sols, for topical pharmaceutical applications. It is also used to suspend powders in aqueous preparations and to prepare cream bases containing oil-in-water emulsifying agents.

Safety

This product is mainly used in topical pharmaceutical preparations, but it is also used in oral pharmaceutical preparations, food industry and cosmetics. After oral administration, this product is not absorbed by the gastrointestinal tract. It is generally believed that this product is a non-toxic and non-irritating substance. LD50 (rat, IV): 0.035 g/kg.

Incompatibilities

The bentonite aqueous suspension maintains its viscosity when the pH value is higher than 6, and settles after adding acid. The acid-washed bentonite has no suspending properties. The addition of alkaline substances such as magnesium oxide helps to form the gel. Adding a large amount of ethanol to the aqueous preparation of this product will dehydrate the network structure and cause bentonite to precipitate. Bentonite is negatively charged, and flocculation can occur when adding electrolytes or positively charged suspensions. Therefore, although electrolytes are beneficial to clear turbid liquids, bentonites are not compatible with electrolytes. The antibacterial efficacy of cationic preservatives decreased in bentonite suspension, while nonionic and anionic preservatives were not affected. Bentonite is not compatible with acriflavine hydrochloride.