POLYDIMETHYLSILOXANE

Chemical Properties

Viscous, greyish-white, opalescent liquid.

Chemical Properties

The PhEur 6.0 and USP 32 describe simethicone as a mixture of fully methylated linear siloxane polymers containing repeating units of the formula [–(CH3)2SiO–]n, stabilized with trimethylsiloxy endblocking units of the formula [(CH3)3 SiO–], and silicon dioxide. It contains not less than 90.5% and not more than 99.0% of the polydimethylsiloxane [–(CH3)2SiO–]n, and not less than 4.0% and not more than 7.0% of silicon dioxide. The PhEur 6.0 additionally states that the degree of polymerization is between 20–400.
Simethicone occurs as a translucent, gray-colored, viscous fluid. It has a molecular weight of 14 000–21 000.

Originator

Mylicon,Stuart,U.S.,1960

Uses

Simethicone Emulsion USP is a water dilutable, non-ionic emulsion containing 30% Simethicone USP by weight. Highly stable over a broad pH range. Simethicones are used as anti foam agents in the manufacture of drugs. Their use in Pharmaceuticals is to comb

Uses

Antifoam A Concentrate has been used as a component of Luria Bertani culture medium for growth of BL21 (DE3) E. coli cells transformed with the plasmids. It has also been used as a constituent in the preparation of aerosol generation fluid.

Uses

Simethicone is an oral anti-foaming agent used to reduce bloating, discomfort and pain caused by excess gas in the stomach or intestinal tract. Simethicone is a mixture of polydimethylsiloxane and hydrated silica gel.

Production Methods

Silicon dioxide is initially rendered hydrophobic in one of a variety of proprietary processes specific to a particular manufacturer. It is then slowly mixed with the silicone fluids in a formulation. After mixing, the simethicone is milled to ensure uniformity.

Manufacturing Process

In a 5 liter three-necked flask, fitted with a reflux condenser, agitator and thermometer, were placed 1,393 g (9.41 mold) of redistilled (CH3)2Si(OEt)2 and 1,110 g (9.41 mols) of (CH3)3SiOEt. To this solution was added 254 g (14.11 mols) of water containing 7.5 g of NaOH (approximately 1 NaOH per 100 silicon atoms). This insured the formation of only straight chain polymers. The mixture was heated to 40°C and the temperature continued to rise for nearly an hour. After adding 50 cc (20% excess) more water, the mixture was refluxed for two hours and then allowed to stand overnight.
Alcohol was then distilled off, until the temperature reached 100°C. 1,706.6 g of distillate was collected. (Theory 1,430 g.) This alcohol was poured into four times its volume of water and an insoluble oil separated (457 g). The insoluble fraction was added back to the copolymer residue from the distillation and 555 cc of 20% hydrochloric acid was added. The acid mixture was refluxed for two hours, and the silicon oils were carefully washed with distilled water until neutral. The yield was 1,420 g. (Theory 1,409 g.)

brand name

Gas-X (Novartis); Mylanta Gas Relief (Johnson & Johnson-Merck Consumer); Mylicon Infant’s Drops (Johnson & Johnson-Merck Consumer); Sentry Simethicone (Witco); Sentry Simethicone Emulsion (Witco).

Therapeutic Function

Antiflatulent

General Description

Antifoam A Concentrate is an extremely effective foam suppressor for aqueous and non-aqueous systems. It is 100% active silicone polymer. No emulsifiers are present. Antifoam A Concentrate is typically effective at 1-100 ppm. Antifoam A Concentrate should be diluted with 3-10 parts of propylene glycol (aqueous) or vegetable oil (nonaqueous) with slow mixing. The product will be stable in the pH range of 5 to 9. Antifoam A Concentrate can be added directly to a fermentation medium, but it is not recommended that it be pumped to a fermenter on an as-needed basis.

Pharmaceutical Applications

The main use of simethicone as an excipient is as an antifoaming agent in pharmaceutical manufacturing processes, for which 1–50 ppm is used.
Therapeutically, simethicone is included in a number of oral pharmaceutical formulations as an antiflatulent, although its therapeutic benefit is questionable. It is also included in antacid products such as tablets or capsules. In some types of surgical or gastroscopic procedures where gas is used to inflate the body cavity, a defoaming preparation containing simethicone may be used in the area to control foaming of the fluids.
When simethicone is used in aqueous formulations, it should be emulsified to ensure compatibility with the aqueous system and components.
In the USA, up to 10 ppm of simethicone may be used in food products.

Safety

Simethicone is used in cosmetics, foods, and oral and topical pharmaceutical formulations, and is generally regarded as a relatively nontoxic and nonirritant material when used as an excipient. Direct contact with the eye may cause irritation.
Therapeutically, oral doses of 125–250mg of simethicone, three or four times daily, have been given as an antiflatulent. Doses of 20–40 mg of simethicone have been given with feeds to relieve colic in infants.
LD50 (dog, IV): 0.9 g/kg

storage

Simethicone is generally regarded as a stable material when stored in the original unopened container. A shelf-life of 18 months from the date of manufacture is typical. However, some simethicone products have a tendency for the silicon dioxide to settle slightly and containers of simethicone should therefore be shaken thoroughly to ensure uniformity of contents before sampling or use. Simethicone should be stored in a cool, dry, location away from oxidizing materials.
Simethicone can be sterilized by dry heating or autoclaving. With dry heating, a minimum of 4 hours at 160℃ is required.

Incompatibilities

Simethicone as supplied is not generally compatible with aqueous systems and will float like an oil on a formulation unless it is first emulsified. It should not be used in formulations or processing conditions that are very acidic (below pH 3) or highly alkaline (above pH 10), since these conditions may have some tendency to break the polydimethylsiloxane polymer. Simethicone cannot normally be mixed with polar solvents of any kind because it is very minimally soluble. Simethicone is incompatible with oxidizing agents.

Regulatory Status

GRAS listed. Included in the FDA Inactive Ingredients Database (oral emulsions, powders, solutions, suspensions, tablets; and rectal and topical preparations). Included in nonparenteral medicines licensed in the UK.