Cellulose acetate

• Ph. Eur.Cellulose Acetate
• USP–NFCellulose Acetate

Acetic acid, cellulose ester; acetyl cellulose; cellulose diacetate; cellulosi acetas; CA-320S; CA-398-10

Cellulose acetate (partially or completely acetylated cellulose) · [9004-35-7]

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

Coating agent, film former, Release-modifying polymer

Typical concentrations: — · Dosage forms: Solid

Used mainly as the semipermeable membrane of osmotic-pump tablets and as a coating or matrix material in controlled-release tablets, beads and pellets; it is also used for taste masking. Release rate is adjusted with plasticisers and water-soluble pore formers such as macrogols.

A white to off-white, free-flowing powder, pellets or flakes. It is tasteless and odourless or has a faint odour of acetic acid.

Acetyl content

29.0–44.8% (USP–NF); common grades about 32% (CA-320) and 39.8% (CA-398)

Solubility

depends on acetyl content: grades with about 39–40% acetyl are soluble in acetone; higher-acetyl (triacetate) grades need methylene chloride; all are practically insoluble in water

Film properties

forms strong films that are permeable to water but much less permeable to dissolved solutes (semipermeable)

Stable when kept dry. Exposure to heat and high humidity causes slow hydrolysis with release of acetic acid. Store in a well-closed container in a cool, dry place.

Incompatible with strongly acidic or alkaline substances, which hydrolyse the ester groups.

Purified cellulose from wood pulp or cotton linters is acetylated with acetic anhydride in acetic acid using a sulfuric acid catalyst to give the triacetate, which is then partially hydrolysed to the required acetyl content.

Regarded as non-toxic and non-irritant; it is not absorbed. The insoluble shells of osmotic tablets pass through the gut intact and may be seen in the stool, which patients should be told about. Non-deformable controlled-release tablets have rarely caused obstruction in patients with pre-existing gastrointestinal narrowing.

Observe normal precautions for the quantity handled. The fine powder can form explosive dust–air mixtures; avoid ignition sources and wear eye protection and a dust mask.

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

Cellulose acetate butyrate; cellulose acetate phthalate; ethylcellulose.

In osmotic-pump tablets the drug is released through a small, usually laser-drilled, orifice in the cellulose acetate coat, giving release that is largely independent of pH and gastrointestinal motility.