Dimethicone

Absorption

The use of dimethicone in skin moisturizers or anti-lice products have proven a very low absorption rate. Studies have indicated that approximately 0.5% of the dose applied to the skin could be considered as bioavailable. When given orally, as it is administered in anti-gas medications, dimethicone 410 is not absorbed or absorbed in very minimal quantities that account only for 0.001-0.2% of the administered dose. Therefore, a minimal to absent dimethicone form can be detected outside of the GI tract.

Toxicity

The reported LD50 in preclinical rat studies after oral administration of dimethicones is 4070 mg/Kg. Long-term use of dimethicone in skin products may cause skin irritation and impaired cell development. Under the FDA, dimethicone is considered as a safe substance for human use.

Description

Dimethicone (polydimethylsiloxane, PDMS) is the answer to dry hands. This flexible polymer, with a backbone of silicon and oxygen instead of carbon, is used in most hand lotions and many cosmetics. Other uses include silly putty, silicone lubricants, silicone caulk, and cutting edge microfluidic devices.

Chemical properties

colourless to slightly yellow liquid

Chemical properties

Dimethicones are clear, colorless liquids available in various viscosities. Dimethicone is a fluid mixture of fully methylated linear siloxane polymers end-blocked with trimethylsiloxy units. Methicone is a linear monomethyl polysiloxane. Dimethicone are safe as used in cosmetic formulations, vulcanization.

The Uses of Dimethicone

dimethicone is a form of silicone used to give products lubricity, slip, and good feel. It can also serve as a formulation defoamer and help reduce the feeling of greasiness that some creams leave on the skin immediately upon application. In addition, dimethicone is reported to protect the skin against moisture loss when used in larger quantities. It improves product flow and spreadability. In combination with other ingredients, dimethicone becomes a good waterproofing material for sunscreen emulsions, and helps reduce the greasiness often seen in high-SPF preparations.

The Uses of Dimethicone

A silicone oil consisting of a mixture of fully methylated linear siloxane polymers end-blocking with trimethylsiloxy units. Commonly used in skin and hair products.

Background

Dimethicone is a silicone-based polymer used as a moisturizer in different skin OTC products. It is formed by repeated polymeric units of -(CH3)2SiO- with a terminal trimethyl siloxy unit. It is currently recognized by the FDA as a skin protectant OTC ingredient for human use in a concentration of 1-30%. The name dimethicone has a lot of nomenclature inconsistencies as it is used to refer to common names, generic names, trade names or even for the listing of mixtures. It is reported that the term dimethicone includes the notation of polydimethylsiloxane and trimethylsiloxy-terminated fluids between 20-30,000 cSt (viscosity).

Indications

Dimethicone is approved as a transdermal drug delivery system. Dimethicone 410 is part of the simethicone element in Dow Corning Q7-2242 LVA which is an antifoam. Some OTC's containing dimethicone are used to relieve the discomfort of infant gas caused by air swallowing or certain formulas or food, to prevent and help rash, to protect and relieve chapped or cracked skin and as an anti-lice agent.

Definition

ChEBI: A polydimethylsiloxane macromolecule, composed of dimethylsiloxane repeating units.

Production Methods

Dimethicone isapoly (dimethylsiloxane) obtained by hydrolysis and polycondensation of dichlorodimethylsilane and chlorotrimethylsilane. The hydrolysis products contain active silanol groups through which condensation polymerization proceeds. By varying the proportions of chlorotrimethylsilane, which acts as a chain terminator, silicones of varying molecular weight may be prepared. Different grades of dimethicone are produced that may be distinguished by a number placed after the name indicating the nominal viscosity. For example, ABIL 20 (Evonik Goldschmidt UK Ltd) has a nominal kinematic viscosity of 18–22mm2/s (18–22cSt).

Indications

Silicone (dimethicone) ointments are excellent water-protective agents because they have an extremely low surface tension and penetrate crevices in the skin to form a plastic-like barrier. Further, they are nontoxic, inert, stable, and water repellent. As such, they are useful as barrier creams in industry or wherever constant or frequent exposure to aqueous compounds is a problem. They will not, however, protect well against solvents, oils, or dusts.

brand name

Sentry Dimethicone (Witco); Sentry Dimethicone Dispension (Witco).

Pharmaceutical Applications

Dimethicones of various viscosities are widely used in cosmetic and pharmaceutical formulations. In topical oil-in-water emulsions dimethicone is added to the oil phase as an antifoaming agent. Dimethicone is hydrophobic and is also widely used in topical barrier preparations. Therapeutically, dimethicone may be used with simethicone in oral pharmaceutical formulations used in the treatment of flatulence. Dimethicone is also used to form a waterrepellent film on glass containers.

Pharmacokinetics

The activity of dimethicone as an anti-flatulent agent prevents the formation of mucus surrounding the gas pockets in the gastrointestinal tract. This allows the formation of big gas bubbles that can be expelled easily. Dimethicone is usually combined with an antacid to confirm the elimination of trapped gas. This particular combination is usually known as simethicone.
The use of dimethicone 410 as an emollient and occlusive agent for the treatment of dry skin conditions has shown to prevent transepidermal water loss which translates into moisturizing of the dry or chapped skin. The effect of dimethicone also reduce flaking and acts as a lubricant which translates into the look of soft, smooth and flexible nature of healthy and young-looking skin.
The use of dimethicone 410 as an anti-lice medication has been reported to effectively cause a lice mortality between 98-100% but the ovicidal effect seems to be limited.

Safety

Dimethicone is generally regarded as a relatively nontoxic and nonirritant material although it can cause temporary irritation to the eyes. In pharmaceutical formulations it may be used in oral and topical preparations. Dimethicones are also used extensively in cosmetic formulations and in certain food applications.
The WHO has set a tentative estimated acceptable daily intake of dimethicone with a relative molecular mass in the range of 200–300 at up to 1.5mg/kg body-weight.
Injection of silicones into tissues may cause granulomatous reactions. Accidental intravascular injection has been associated with fatalities.

Metabolism

Dimethicone 410 is not metabolized and it is excreted unchanged.

storage

Dimethicones should be stored in an airtight container in a cool, dry, place; they are stable to heat and are resistant to most chemical substances although they are affected by strong acids. Thin films of dimethicone may be sterilized by dry heat for at least 2 hours at 160°C. Sterilization of large quantities of dimethicone by steam autoclaving is notrecommended since excesswater diffuses intothe fluid causing it to become hazy. However, thin films may be sterilized by this method. Gamma irradiation may also be used to sterilize dimethicone. Gamma irradiation can, however, cause crosslinking with a consequent increase in the viscosity of fluids.

Regulatory Status

Accepted for use as a food additive in Europe. Included in the FDA Inactive Ingredients Database (oral capsules and tablets, topical creams,emulsions,lotions,and transdermal preparations).Included in nonparenteral medicines licensed in the UK. Included in the Canadian List of Acceptable Non-medicinal Ingredients.