Propylene Glycol

Abstract

Propylene glycol is a water-soluble fluid that is considered by the US Food and Drug Administration safe for use in foods, drugs, and cosmetics. Its attractive property as a solvent, humectant, or antifreeze, along with a low level of toxicity, has led to its widespread use in commercial and industrial products. The amount of propylene glycol in most products is small and its environmental consequences are minimal due to limited human exposures and a rapid biodegradation. Propylene glycol is used in many oral, topical, and intravenous pharmaceuticals. In particular, drugs such as lorazepam and diazepam that are used for continuous sedation over several days contain high concentrations (0.8gml−1) of propylene glycol. The most likely human exposure to lead to health effects is its use as a solvent in the intravenous medications. Oral propylene glycol is rapidly and extensively absorbed, followed by rapid distribution to tissues in proportion to body water. Propylene glycol is eliminated from the body by a combination of metabolic clearance and renal excretion. Commercial propylene glycol exists as an equal mixture of d and l stereoisomers, so its metabolism results in the formation of both d and l forms of lactate. Propylene glycol has a low degree of toxicity in animals as well as humans, such that very high doses are needed to elicit effects in acute toxicity studies. Central nervous system depression, hematologic toxicity, hyperosmolarity, metabolic acidosis, cardiovascular effects, and renal toxicity encompass the main acute and subacute syndromes for propylene glycol. These effects result from high concentrations of the parent molecule or the accumulation of d,l-lactate in the blood. Current exposures to propylene glycol are of negligible concern for reproductive or developmental toxicity or for carcinogenesis in humans.