Carbomer

• BPCarbomers
• Ph. Eur.Carbomers
• USP–NFCarbomer Homopolymer; Carbomer Copolymer; Carbomer Interpolymer

Acritamer; acrylic acid polymer; carbomera; Carbopol; carboxy polymethylene; carboxyvinyl polymer; Pemulen; polyacrylic acid; Tego Carbomer

High-molecular-weight polymers of acrylic acid crosslinked with allyl ethers of sucrose or pentaerythritol · [9003-01-4]

(C3H4O2)n (repeat unit) · estimated 7 × 10⁵ to 4 × 10⁹

Gelling agent, viscosity modifier

Typical concentrations: 0.5–2% gel · 0.5–1% suspending · 0.1–0.5% emulsifying · Dosage forms: Semi-solid, Liquid

Used mainly as rheology modifiers in liquid and semisolid preparations, such as gels, creams, lotions and suspensions, including ophthalmic, rectal, topical and vaginal products. Some grades act as primary polymeric emulsifiers, and carbomers are also used as tablet binders, controlled-release matrix formers and bioadhesives. Typical concentrations: emulsifying agent 0.1–0.5%; gelling agent 0.5–2.0%; suspending agent 0.5–1.0%; tablet binder 0.75–3.0%; controlled-release agent 5.0–30.0%.

A white, fluffy, acidic, hygroscopic powder with a slight characteristic odour. Grades differ in crosslink density, polymerisation solvent and the viscosity they give when neutralised.

Carboxylic acid content

56.0–68.0% (dried substance)

pKa

≈ 6.0 ± 0.5

pH

≈ 2.5–3.5 (0.5–1% w/v aqueous dispersion)

Viscosity

low as an acidic dispersion; rises sharply on neutralisation, with the level depending on grade and concentration

Moisture content

hygroscopic; typically not more than 2% as supplied

Solubility

does not dissolve but swells in water, glycerol and, after neutralisation, ethanol (95%)

The dry powder is stable and does not support microbial growth, but aqueous gels do and need a preservative. Gels lose viscosity on prolonged exposure to light; this is reduced by adding an antioxidant or a chelating agent such as edetate. Store in an airtight container in a cool, dry place.

Discoloured by resorcinol and incompatible with phenol, cationic polymers, strong acids and high concentrations of electrolytes, which reduce gel viscosity. Trace iron and other transition metals catalyse its degradation, and cationic drugs may form insoluble complexes.

Made by polymerising acrylic acid with a polyalkenyl ether crosslinker in an organic solvent. Older grades were polymerised in benzene; current grades use ethyl acetate or cyclohexane–ethyl acetate mixtures.

Regarded as essentially non-toxic and non-irritant when used in topical and oral products; its high molecular weight prevents absorption. The powder can irritate the eyes.

The dust may irritate the eyes, mucous membranes and respiratory tract. Wear gloves, eye protection and a dust respirator, and avoid creating airborne dust.

Included in the FDA Inactive Ingredient Database (ophthalmic, oral, rectal, topical and vaginal preparations) and in non-parenteral medicines licensed in Europe.

Polycarbophil; calcium polycarbophil; polyacrylates.

Disperse the powder slowly into vigorously stirred water to avoid lumps, then neutralise with a base such as sodium hydroxide, triethanolamine or trometamol; maximum viscosity is usually reached around pH 6–7.5. Grades polymerised in benzene are subject to residual-solvent limits and have largely been replaced.