Simethicone

• BPSimeticone
• Ph. Eur.Simeticone
• USP–NFSimethicone

Activated dimethicone; activated polymethylsiloxane; simeticone; dimethicone with silicon dioxide; silicone antifoam

Mixture of fully methylated linear siloxane polymers (dimethicone) with finely divided silicon dioxide · [8050-81-5]

[–(CH3)2SiO–]n with SiO2

Semi-solid base, emollient

Typical concentrations: — · Dosage forms: Liquid, Solid

Simethicone is used as an antifoaming agent: as an active ingredient in antiflatulent products, and as a processing aid to suppress foaming during the manufacture of liquids, emulsions and fermentation products. It is also used in topical barrier preparations and as a defoamer in oral suspensions. It is effective at low concentrations, usually well below 1% of the product, often supplied as an aqueous emulsion for ease of dispersion.

A translucent, grey, viscous fluid. Pharmacopoeial material contains about 90.5–99.0% polydimethylsiloxane and 4.0–7.0% silicon dioxide; the silica particles are hydrophobised by the silicone, which makes the mixture a much more effective defoamer than dimethicone alone.

Silicon dioxide content

4.0–7.0%

Defoaming activity

foam collapses within 15 seconds in the pharmacopoeial test

Solubility

practically insoluble in water and ethanol; the polysiloxane fraction is soluble in toluene, chloroform and ether, leaving the silica as a residue

Appearance

grey, translucent, viscous liquid

Chemically stable and resistant to oxidation. Simethicone emulsions may separate if frozen or exposed to high temperatures. Store in a well-closed container.

Few incompatibilities have been reported. Silicone antifoams can be deactivated by strong emulsifiers and surfactants, and may interfere with the wetting of tablet surfaces in film coating.

Prepared by dispersing finely divided silicon dioxide (silica) in dimethicone and treating the mixture, usually with heat, so that the silica surface becomes coated with the silicone. Dimethicone itself is made by hydrolysis and polycondensation of dichlorodimethylsilane with chlorotrimethylsilane as a chain stopper.

Simethicone is physiologically inert, is not absorbed from the gastrointestinal tract and is regarded as non-toxic and non-irritant. It is given orally in relatively large doses as an antiflatulent without significant adverse effects.

Observe normal precautions for the quantity handled. Spills are very slippery and should be cleaned up promptly; eye protection is recommended.

Included in the FDA Inactive Ingredient Database (oral preparations) and in non-parenteral medicines licensed in Europe. Simethicone is also an FDA monograph active ingredient for over-the-counter antiflatulent products.

Dimethicone; cyclomethicone; colloidal silicon dioxide.

When used as a processing antifoam, add the minimum amount needed, since excess silicone can cause oily films, turbidity or poor adhesion of later coating layers. Pre-dilution or use of an emulsion grade helps uniform dispersion in aqueous systems.