Functional Category
Antimicrobial preservative
Applications in Pharmaceutical Formulation
Butylparaben is widely used as an antimicrobial preservative in cosmetics and pharmaceutical formulations; see Table I. It may be used either alone or in combination with other paraben esters or with other antimicrobial agents. In cosmetics, it is the fourth most frequently used preservative.(1) As a group, 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, paraben salts, particularly the sodium salt, are frequently used in formulations. However, this may raise the pH of poorly buffered formulations.
Description
Butylparaben occurs as colorless crystals or a white, crystalline, odorless or almost odorless, tasteless powder
Stability and Storage Conditions
Aqueous butylparaben 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 butylparaben is considerably reduced in the presence of nonionic surfactants as a result of micellization.(6) Absorption of butylparaben by plastics has not been reported but appears probable given the behavior of other parabens. Some pigments, e.g. ultramarine blue and yellow iron oxide, absorb butylparaben and thus reduce its preservative properties.(7) Butylparaben is discolored in the presence of iron and is subject to hydrolysis by weak alkalis and strong acids.
Safety
Butylparaben and other parabens are widely used as antimicrobial preservatives in cosmetics and oral and topical pharmaceutical formulations. Systemically, no adverse reactions to parabens have been reported, although they have been associated with hypersensitivity reactions generally appearing as contact dematitis. Immediate reactions with urticaria and bronchospasm have occurred rarely. See Methylparaben for further information. LD50 (mouse, IP): 0.23 g/kg(8) LD50 (mouse, oral): 13.2 g/kg