Stearic acid

• BPStearic Acid
• JPStearic Acid
• Ph. Eur.Stearic Acid
• USP–NFStearic Acid

cetylacetic acid; Crodacid; Emersol; Hystrene; Industrene; octadecanoic acid; Pristerene; acidum stearicum; E570

Octadecanoic acid · [57-11-4]

UNII 4ELV7Z65AP · PubChem CID 5281

C18H36O2 · 284.48

Lubricant

Typical concentrations: 1–3% · Dosage forms: Solid, Semi-solid

Used in oral products mainly as a tablet and capsule lubricant, and also as a binder and as a matrix or coating material in sustained-release forms. In topical products it is an emulsifying and solubilising agent and stiffener; partly neutralised with an alkali or triethanolamine it forms the soap-based emulsifier of 'vanishing' creams. It is also a hardening agent in suppositories. Typical concentrations: tablet lubricant 1–3% w/w; ointments and creams 1–20% w/w.

A hard, white or faintly yellow, somewhat glossy crystalline solid, or a white to yellowish-white powder, with a slight odour and taste suggesting tallow. The pharmaceutical material is a mixture of stearic and palmitic acids; Ph. Eur. describes types 50, 70 and 95 according to their nominal stearic acid content.

Melting point

about 54–69 °C depending on grade (pure stearic acid ≈ 69 °C)

Acid value

≈ 194–212

Iodine value

not more than about 4

Solubility

freely soluble in chloroform and ether; soluble in ethanol (95%), hexane and propylene glycol; practically insoluble in water

Stable; an antioxidant may be added. Store in a well-closed container in a cool, dry place.

Incompatible with most metal hydroxides and with oxidising agents. It forms insoluble stearates with many metals, so ointment bases containing stearic acid may become dry or lumpy when compounded with zinc or calcium salts.

Obtained by hydrolysis (fat splitting) of animal fats or of vegetable oils such as hydrogenated palm or cottonseed oil; the fatty acid mixture is hydrogenated and separated by distillation, pressing or crystallisation to give the required stearic acid content.

Widely used in oral and topical products and in foods, and regarded as non-toxic and non-irritant. It is a normal component of dietary fat.

Observe normal precautions for the quantity handled. Eye protection and gloves are recommended, and a dust mask where dust is generated. It is combustible.

GRAS listed. Accepted in Europe as a food additive (E570). Included in the FDA Inactive Ingredient Database (oral capsules and tablets, sublingual tablets, topical and vaginal preparations) and in non-parenteral medicines licensed in Europe.

Calcium stearate; magnesium stearate; palmitic acid; zinc stearate; stearyl alcohol.

As a tablet lubricant stearic acid is less efficient than magnesium stearate but is less likely to slow dissolution or interact with drugs that are sensitive to alkaline earth salts. Grades differ in stearic:palmitic ratio and in source (animal or vegetable), which affects melting behaviour and suitability for some markets.