Propylene glycol

• BPPropylene Glycol
• JPPropylene Glycol
• Ph. Eur.Propylene Glycol
• USP–NFPropylene Glycol

1,2-dihydroxypropane; 2-hydroxypropanol; methyl ethylene glycol; methyl glycol; propane-1,2-diol; propylenglycolum; E1520

1,2-Propanediol · [57-55-6]

UNII 6DC9Q167V3 · PubChem CID 1030

C3H8O2 · 76.09

Solvent, humectant, Antimicrobial preservative

Typical concentrations: ≈15% humectant · 10–25% oral cosolvent · Dosage forms: Liquid, Semi-solid

A widely used solvent and cosolvent in parenteral and non-parenteral products; it is a better general solvent than glycerin and dissolves many drugs, vitamins and essential oils. It also acts as a humectant, antimicrobial preservative, plasticiser for film coatings and carrier for flavours. Typical concentrations: solvent or cosolvent in aerosol solutions 10–30%, oral solutions 10–25%, parenterals 10–60% and topicals 5–80%; humectant in topicals about 15%; preservative in solutions and semisolids 15–30%.

A clear, colourless, viscous, practically odourless liquid with a sweet, slightly acrid taste resembling that of glycerin. It is hygroscopic.

Boiling point

≈ 188 °C

Melting point

≈ −59 °C

Density

≈ 1.038 g/cm³ at 20 °C

Viscosity (dynamic)

≈ 58 mPa s at 20 °C

Flash point

≈ 99 °C (open cup)

Solubility

miscible with water, acetone, chloroform, ethanol (95%) and glycerin; not miscible with fixed oils or light mineral oil, though it dissolves some essential oils

Stable in a well-closed container at cool temperatures, but at high temperatures in the open air it oxidises to products such as propionaldehyde and lactic, pyruvic and acetic acids. It is chemically stable when mixed with ethanol, glycerin or water, and aqueous solutions can be sterilised by autoclaving. Being hygroscopic, it should be stored in a well-closed container, protected from light, in a cool, dry place.

Incompatible with oxidising agents such as potassium permanganate.

Made mainly by hydration of propylene oxide, which is itself obtained from propylene; the glycol is then purified by distillation. Routes from glycerol (for example by catalytic hydrogenolysis of bio-based glycerol) are also used.

Used in a wide range of medicines, foods and cosmetics and generally regarded as relatively non-toxic. Large doses, particularly in neonates and young children whose ability to metabolise it is limited, have been associated with CNS depression, hyperosmolality and lactic acidosis. Rapid intravenous injection of products with a high propylene glycol content can cause local pain, haemolysis and cardiovascular effects. Topically it can be mildly irritant and occasionally causes contact dermatitis.

Observe normal precautions for the quantity handled. Eye protection and gloves are recommended. It is combustible; handle in a well-ventilated area away from ignition sources.

GRAS listed. Accepted in Europe as a food additive (E1520). Included in the FDA Inactive Ingredient Database (including dental, inhalation, intramuscular, intravenous, oral, otic, rectal, topical, transdermal and vaginal preparations) and in parenteral and non-parenteral medicines licensed in Europe; the EMA requires label warnings above set daily exposure thresholds.

Glycerin; polyethylene glycol; propylene glycol alginate; propylene carbonate.

EMA guidance sets labelling thresholds of 1 mg/kg/day for neonates up to 4 weeks, 50 mg/kg/day for children under 5 years and 500 mg/kg/day for older children and adults; these should be considered when formulating paediatric and parenteral products. Its antimicrobial activity is similar to that of ethanol, and it is often used to enhance the efficacy of other preservatives.