International Numbering System (INS) for Food Additives: 431
Food additives Europe numbers: E431
Functional Category:
Emulsifying agent; solubilizing agent; wetting agent.
Applications in Pharmaceutical Formulation
Polyoxyethylene stearates are generally used as emulsifiers in oil-inwater-type creams and lotions. Their hydrophilicity or lipophilicity depends on the number of ethylene oxide units present: the larger the number, the greater the hydrophilic properties. Polyoxyl 40 stearate has been used as an emulsifying agent in intravenous infusions.(1) Polyoxyethylene stearates are particularly useful as emulsifying agents when astringent salts or other strong electrolytes are present. They can also be blended with other surfactants to obtain any hydrophilic–lipophilic balance for lotions or ointment formulations.
Stability and Storage Conditions
Polyoxyethylene stearates are generally stable in the presence of electrolytes and weak acids or bases. Strong acids and bases can cause gradual hydrolysis and saponification. The bulk material should be stored in a well-closed container, in a dry place, at room temperature.
Incompatibilities
Polyoxyethylene stearates are unstable in hot alkaline solutions owing to hydrolysis, and will also saponify with strong acids or bases. Discoloration or precipitation can occur with salicylates, phenolic substances, iodine salts, and salts of bismuth, silver, and tannins.(2–4) Complex formation with preservatives may also occur.(5) The antimicrobial activity of some materials such as bacitracin, chloramphenicol, phenoxymethylpenicillin, sodium penicillin, and tetracycline may be reduced in the presence of polyoxyethylene stearate concentrations greater than 5% w/w.(6,7)
Safety
Although polyoxyethylene stearates are primarily used as emulsifying agents in topical pharmaceutical formulations, certain materials, particularly polyoxyl 40 stearate, have also been used in intravenous injections and oral preparations.(1,4) Polyoxyethylene stearates have been tested extensively for toxicity in animals(8–13) and are widely used in pharmaceutical formulations and cosmetics. They are generally regarded as essentially nontoxic and nonirritant materials. Polyoxyl 8 stearate LD50 (hamster, oral): 27 g/kg LD50 (rat, oral): 64 g/kg Polyoxyl 20 stearate LD50 (mouse, IP): 0.2 g/kg LD50 (mouse, IV): 0.87 g/kg