Propylparaben

• BPPropyl Parahydroxybenzoate
• JPPropyl Parahydroxybenzoate
• Ph. Eur.Propyl Parahydroxybenzoate
• USP–NFPropylparaben

propyl 4-hydroxybenzoate; propyl p-hydroxybenzoate; propyl parahydroxybenzoate; propylis parahydroxybenzoas; Nipasol M; Solbrol P

Propyl 4-hydroxybenzoate · [94-13-3]

UNII Z8IX2SC1OH · PubChem CID 7175

C10H12O3 · 180.20

Antimicrobial preservative

Typical concentrations: 0.01–0.02% oral · 0.01–0.6% topical · Dosage forms: Liquid, Semi-solid

An antimicrobial preservative widely used in cosmetics, foods and pharmaceutical products, usually combined with methylparaben (for example methylparaben 0.18% with propylparaben 0.02% in parenterals) or with other preservatives to widen the spectrum. The parabens are effective over a wide pH range (about 4–8) and are more active against yeasts and moulds than against bacteria. Typical concentrations: oral solutions and suspensions 0.01–0.02%; injections 0.005–0.2%; topical preparations 0.01–0.6%.

White crystals or a white crystalline powder, odourless and tasteless.

Melting point

96–99 °C

pKa

≈ 8.4

Solubility

very slightly soluble in water (about 1 in 2500 at 20 °C); freely soluble in ethanol, acetone and ether; soluble in propylene glycol

Effective pH range

about 4–8; activity falls at higher pH as the phenolate ion forms

Aqueous solutions at pH 3–6 are stable for long periods at room temperature and can be sterilised by autoclaving without significant loss, whereas at pH 8 and above hydrolysis to 4-hydroxybenzoic acid is rapid. Store in a well-closed container in a cool, dry place.

Antimicrobial activity is markedly reduced by non-ionic surfactants such as polysorbate 80, through micellar binding, and by some macromolecules. It can be sorbed by plastics and adsorbed by magnesium trisilicate and magnesium aluminium silicate. Iron salts cause discolouration, and it is hydrolysed by alkalis and strong acids.

Prepared by esterifying 4-hydroxybenzoic acid with propan-1-ol in the presence of an acid catalyst, followed by purification by crystallisation.

Widely used and generally regarded as of low toxicity. Hypersensitivity reactions, mainly delayed-type contact dermatitis, are the most common adverse effects; immediate reactions after injection are rare. Because of effects on male reproductive parameters seen in juvenile rats, EFSA excluded propylparaben from the group ADI for parabens, and the EMA has proposed a permitted daily exposure of 2 mg/kg/day for oral medicines.

Observe normal precautions for the quantity handled. The powder may irritate the eyes, skin and respiratory tract; eye protection, gloves and a dust mask are recommended.

GRAS listed in the USA. Its former E-number (E216) was withdrawn and it is no longer permitted as a food additive in the EU; in EU cosmetics its use is restricted. Included in the FDA Inactive Ingredient Database (injections, inhalation, ophthalmic, oral, otic, rectal, topical and vaginal preparations) and in parenteral and non-parenteral medicines licensed in Europe.

Butylparaben; ethylparaben; methylparaben; propylparaben sodium.

Because of its low water solubility, propylparaben is usually dissolved in hot water, in propylene glycol or in ethanol before addition, or the more soluble sodium salt is used (which raises the pH). The EMA reflection paper on parabens asks that its use in paediatric oral medicines be justified.