Food additives Europe numbers: E216
Functional Category
Antimicrobial preservative.
Applications in Pharmaceutical Formulation
Propylparaben is widely used as an antimicrobial preservative in cosmetics, food products, and pharmaceutical formulations; see Table I. It may be used alone, in combination with other paraben esters, or with other antimicrobial agents. It is one of the most frequently used preservatives in cosmetics.(1) The parabens are effective over a wide pH range and have a broad spectrum of antimicrobial activity, although they are most effective against yeasts and molds; see Section 10. Owing to the poor solubility of the parabens, the paraben salts, particularly the sodium salt, are frequently used in formulations. This may cause the pH of poorly buffered formulations to become more alkaline. Propylparaben (0.02% w/v) together with methylparaben (0.18% w/v) has been used for the preservation of various parenteral pharmaceutical formulations; see Section 14. See Methylparaben for further information.
Description
Propylparaben occurs as a white, crystalline, odorless, and tasteless powder.
Stability and Storage Conditions
Aqueous propylparaben solutions at pH 3–6 can be sterilized by autoclaving, without decomposition.(4) At pH 3–6, aqueous solutions are stable (less than 10% decomposition) for up to about 4 years at room temperature, while solutions at pH 8 or above are subject to rapid hydrolysis (10% or more after about 60 days at room temperature).(5)
Incompatibilities
The antimicrobial activity of propylparaben is reduced considerably in the presence of nonionic surfactants as a result of micellization.(6) Absorption of propylparaben by plastics has been reported, with the amount absorbed dependent upon the type of plastic and the vehicle.(7) Magnesium aluminum silicate, magnesium trisilicate, yellow iron oxide, and ultramarine blue have also been reported to absorb propylparaben, thereby reducing preservative efficacy.(8,9) Propylparaben is discolored in the presence of iron and is subject to hydrolysis by weak alkalis and strong acids. See also Methylparaben
Safety
Propylparaben and other parabens are widely used as antimicrobial preservatives in cosmetics, food products, and oral and topical pharmaceutical formulations. Propylparaben and methylparaben have been used as preservatives in injections and ophthalmic preparations; however, they are now generally regarded as being unsuitable for these types of formulations owing to the irritant potential of the parabens. Systemically, no adverse reactions to parabens have been reported, although they have been associated with hypersensitivity reactions. The WHO has set an estimated acceptable total daily intake for methyl, ethyl, and propyl parabens at up to 10 mg/kg body-weight.(10) LD50 (mouse, IP): 0.2 g/kg(11) LD50 (mouse, oral): 6.33 g/kg LD50 (mouse, SC): 1.65 g/kg