Wax, anionic emulsifying

• BPEmulsifying Wax
• Ph. Eur.Cetostearyl Alcohol (Type A), Emulsifying
• Ph. Eur.Cetostearyl Alcohol (Type B), Emulsifying

Anionic emulsifying wax; emulsifying wax BP; emulsifying cetostearyl alcohol; Lanette Wax SX; Lanette N

Mixture of cetostearyl alcohol and an anionic surfactant (sodium lauryl sulfate or sodium cetostearyl sulfate) · [—]

Polymer, mixture or material of variable composition — no single molecular formula applies.

Surfactant, emulsifier, Semi-solid base, emollient

Typical concentrations: — · Dosage forms: Semi-solid

Used as an emulsifying agent and stiffener to make o/w creams and emulsifying ointments. Classic examples are Emulsifying Ointment BP (30% emulsifying wax with white soft paraffin and liquid paraffin) and Aqueous Cream BP, which contains 30% emulsifying ointment.

A white or pale yellow waxy solid or flakes with a faint characteristic odour. It becomes plastic when warm and melts to a clear liquid. On mixing with water when melted it forms stable o/w emulsions.

Composition (BP)

cetostearyl alcohol 9 parts and sodium lauryl sulfate 1 part, with a small amount of water

Melting range

about 50–56 °C

Solubility

soluble in ether and chloroform, partly soluble in ethanol (95%); practically insoluble in water but forms emulsions when melted with water

Ionic character

anionic

Physical form

white or pale yellow waxy solid or flakes

Stable. Store in a well-closed container in a cool, dry place. Creams made from it need an antimicrobial preservative.

Because of its anionic surfactant it is incompatible with cationic compounds, such as quaternary ammonium antiseptics and many basic drugs, and with polyvalent metal ions; high electrolyte concentrations and strongly acidic conditions may destabilise emulsions.

Made by melting cetostearyl alcohol, adding sodium lauryl sulfate (or sodium cetostearyl sulfate) and a little water, heating with stirring until the water is removed and a homogeneous mass is obtained, and then cooling and flaking.

Used widely in topical products and generally regarded as non-toxic. The sodium lauryl sulfate component can irritate the skin; Aqueous Cream BP used as a leave-on emollient has been associated with stinging and skin irritation, particularly in children with eczema, and is better used as a soap substitute.

Observe normal precautions for the quantity handled. Take care with the hot molten wax; eye protection and gloves are recommended.

Included in non-parenteral (topical) medicines licensed in the UK and Europe.

Cetostearyl alcohol; sodium lauryl sulfate; wax, nonionic emulsifying; cetrimide emulsifying wax (cationic).

Choose the emulsifying wax according to the charge of the drug: anionic wax for neutral or anionic drugs, nonionic (cetomacrogol) wax where electrolytes or a wide pH range are involved, and cationic wax with cationic drugs. Ph. Eur. describes two emulsifying cetostearyl alcohols: Type A contains sodium cetostearyl sulfate and Type B sodium lauryl sulfate.