Polyvinyl acetate phthalate

• USP–NFPolyvinyl Acetate Phthalate

Opaseal; PVAP; Sureteric; phthalic acid, polymer with vinyl acetate and vinyl alcohol

Partial phthalate ester of partially hydrolysed polyvinyl acetate (a reaction product of phthalic anhydride and partially hydrolysed polyvinyl acetate) · [34481-48-6]

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, applied either from organic solvent solutions or as aqueous dispersions of fully formulated systems; it is also used as a moisture-protective seal coat on tablet cores before sugar coating. Enteric coatings typically require a weight gain of several percent, with a plasticiser such as triethyl citrate or polyethylene glycol.

A vinyl polymer in which part of the hydroxyl groups of partially hydrolysed polyvinyl acetate are esterified with phthalic acid, giving free carboxyl groups that ionise in neutral to mildly acidic intestinal fluid. It is a white to off-white, free-flowing powder.

Physical form

free-flowing white to off-white powder, sometimes with a slight odour of acetic acid

Phthalyl content

about 55–62% (dried, acid-free basis)

Dissolution pH

insoluble in gastric fluid; dissolves above about pH 5

Solubility

soluble in methanol and ethanol–water mixtures and in alkaline buffer; practically insoluble in water and dichloromethane

More resistant to hydrolysis than cellulose acetate phthalate, but exposure to heat and moisture slowly releases free phthalic and acetic acids, which can impair enteric performance. Store in a well-closed container in a cool, dry place.

Incompatible with strong oxidising agents and with alkaline substances that ionise or hydrolyse the phthalate groups. Its acidic groups may interact with basic drugs in direct contact.

Prepared by esterifying partially hydrolysed polyvinyl acetate (a low-molecular-weight polyvinyl alcohol containing residual acetate groups) with phthalic anhydride in the presence of sodium acetate, followed by purification.

Used in oral solid dosage forms and regarded as non-toxic and non-irritant; the polymer is not significantly absorbed from the gastrointestinal tract.

Observe normal precautions for the quantity handled. Avoid dust inhalation; eye protection, gloves and a dust mask are recommended. Organic coating solutions are flammable.

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

Cellulose acetate phthalate; hypromellose phthalate; polymethacrylates; shellac.

Polyvinyl acetate phthalate dissolves at a relatively low pH among enteric polymers, so drug release begins early in the duodenum. Free phthalic acid content should be monitored on storage, since it increases as the polymer hydrolyses.