Cellulose acetate phthalate

• BPCellacefate
• JPCellacefate
• Ph. Eur.Cellulose Acetate Phthalate
• USP–NFCellacefate

CAP; cellacefate; acetyl phthalyl cellulose; cellulose acetate hydrogen phthalate; cellulosi acetas phthalas; Aquacoat CPD; Eastman C-A-P

Cellulose, acetate, 1,2-benzenedicarboxylate (partial acetate and phthalate ester of cellulose) · [9004-38-0]

Polymer, mixture or material of variable composition — no single molecular formula applies.

Coating agent, film former

Typical concentrations: — · Dosage forms: Solid

Used as an enteric film coating for tablets and capsules, which resists the acid of the stomach and dissolves in the small intestine, and as a matrix former in granules and tablets for modified release. Coatings are usually applied at about 0.5–9.0% of the core weight from organic solvent solutions or from aqueous dispersions or ammonium-salt solutions, with a plasticiser such as diethyl phthalate, triacetin or triethyl citrate.

A hygroscopic, white to off-white, free-flowing powder, granules or flakes. It is tasteless and odourless, or may have a faint odour of acetic acid.

Acetyl content

21.5–26.0% (USP-NF, anhydrous, acid-free basis)

Phthalyl content

30.0–36.0% (USP-NF, anhydrous, acid-free basis)

Free acid

not more than 6.0% (calculated as phthalic acid)

Dissolution pH

insoluble in acidic gastric fluid; dissolves in aqueous media above about pH 6

Solubility

practically insoluble in water, ethanol and chlorinated or aliphatic hydrocarbons; soluble in acetone, dioxane and certain solvent mixtures such as acetone–ethanol

Water content

not more than 5.0% (hygroscopic)

Slowly hydrolysed under prolonged exposure to high temperature and humidity, which increases the free acid content, changes viscosity and produces an odour of acetic acid; this can impair enteric performance. Store in a well-closed container in a cool, dry place.

Incompatible with ferrous sulfate, ferric chloride, silver nitrate, sodium citrate, aluminium sulfate, calcium chloride, mercuric chloride, barium nitrate and basic lead acetate, and with strong oxidising agents, strong alkalis and acids. Its free carboxylic groups may also interact with basic drugs.

Made by reacting a partial acetate ester of cellulose with phthalic anhydride in the presence of a tertiary organic base such as pyridine, or of a strong acid catalyst such as sulfuric acid.

Used in oral products and generally regarded as non-toxic and non-irritant; it is not significantly absorbed from the gastrointestinal tract.

Observe normal precautions for the quantity handled. Eye protection, gloves and a dust mask are recommended. Organic solvent coating solutions require precautions appropriate to the flammable solvents used.

Included in the FDA Inactive Ingredient Database (oral tablets and capsules) and in non-parenteral medicines licensed in Europe.

Cellulose acetate; hypromellose phthalate; hypromellose acetate succinate; polyvinyl acetate phthalate; methacrylic acid copolymers.

CAP films are somewhat permeable to water and certain ionic species, so moisture-sensitive cores may need a sealing subcoat, and enteric coats should be checked after storage at high humidity because hydrolysis can lead to premature release. Because its dissolution threshold (about pH 6) is relatively high, release may be delayed until the lower small intestine.