Products
As a pure substance, propylene glycol is available in pharmacies and drugstores, among other places. It is contained in many medicines, medical devices and cosmetics, for example in gels, creams, preparations for inhalation, injectables and film-coated tablets.
Structure and properties
Propylene glycol or propane-1,2-diol (C3H8O2, Mr = 76.1 g/mol) is a racemate. It exists as a clear, colorless, viscous, hygroscopic liquid with a sweetish taste and is miscible with water, ethanol, and acetone. Propylene glycol is a dihydric aliphatic alcohol and a glycol related to the triol glycerol . Like the latter, it is also esterified with fatty acids to form mono- and diesters. The boiling point is about 189°C and the density is only slightly above that of water.
Applications
Propylene glycol is used as a solvent and as an excipient for liquid, semisolid, and solid pharmaceuticals, among others, for example, as a humectant, a preservative, a solubilizer, to promote dermal drug absorption, and as an emollient. It is also used as an additive for food and animal feed, as a humectant for tobacco, and it has numerous technical applications (e.g., deicing fluid, synthesis, antifreeze). Propylene glycol is also an important ingredient in e-cigarette liquids and is found in snus.
Dosage
Propylene glycol enters the body in the form of drugs by dermal, peroral, rectal, and inhalation routes, among others.
Adverse effects
Propylene glycol is generally considered well tolerated and has GRAS (generally recognized as safe) status. It can also be ingested in defined amounts. Adverse effects may occur only in severe overdose because metabolism is saturable. The eyes can be easily irritated by propylene glycol. Smoking tobacco products to which propylene glycol is added is considered harmful to health because toxic metabolites are formed. It is also controversial in e-cigarettes.
