Chemical Properties
Polyvinyl acetate phthalate is a free-flowing white to off-white
powder and may have a slight odor of acetic acid. The material is
essentially amorphous.
Production Methods
Polyvinyl acetate phthalate is a reaction product of phthalic
anhydride, sodium acetate, and a partially hydrolyzed polyvinyl
alcohol. The polyvinyl alcohol is a low molecular weight grade, and
87–89 mole percent is hydrolyzed. Therefore, the polyvinyl acetate
phthalate polymer is a partial esterification of a partially hydrolyzed
polyvinyl acetate.
Pharmaceutical Applications
Polyvinyl acetate phthalate is a viscosity-modifying agent that is
used in pharmaceutical formulations to produce enteric coatings for
products and for the core sealing of tablets prior to a sugar-coating
process. Polyvinyl acetate phthalate does not exhibit tackiness
during coating and produces strong robust films.
Plasticizers are often included in polyvinyl acetate phthalate
coating formulations to enable a continuous, homogeneous,
noncracking film to be produced. Polyvinyl acetate phthalate has
been shown to be compatible with several plasticizers such as
glyceryl triacetate, triethyl citrate, acetyl triethylcitrate, diethyl
phthalate and polyethylene glycol 400.
For enteric coating applications, polyvinyl acetate phthalate is
dissolved in a solvent system together with other additives such as
diethyl phthalate and stearic acid. Methanol may be used as the
solvent if a colorless film is required; for a colored film, methanol or
ethanol/water may be used depending on the amount of pigment to
be incorporated. A weight increase of up to 8% is necessary for nonpigmented systems, whereas for pigmented systems a weight
increase of 6% is usually required. A formulated, aqueous-based
coating solution ( Sureteric, Colorcon) is available commercially for
the enteric coating of tablets, hard and soft gelatin capsules and
granules. More recently, hot-melt extrusion of coating polymers,
such as polyvinyl acetate phthalate, has been described for the
enteric coating of capsules.
Polyvinyl acetate phthalate has superseded materials such as
shellac in producing the initial layers of coating (the sealing coat) in
the sugar coating process for tablets. The sealing coating should be
kept as thin as possible while providing an adequate barrier to
moisture, a balance that is often difficult to achieve in practice. A
solvent system containing a high proportion of industrial methylated
spirits and other additives can be used. Two coats are usually
sufficient to seal most tablets, although up to five may be necessary
for tablets containing alkaline ingredients. If an enteric coating is
also required, between six and 12 coats may be necessary;
The properties of polyvinyl acetate phthalate enteric coating
have been compared with those of other enteric polymers such as
cellulose acetate phthalate and Eudragit L 30D.The factors
that affect the release kinetics from polyvinyl acetate phthalate
enteric-coated tablets have also been described.A method for
enteric coating hypromellose capsules which avoids the sealing step
prior to coating has been developed. The properties of several
enteric coating polymers, including polyvinyl acetate phthalate,
were assessed.
Safety
Polyvinyl acetate phthalate is used in oral pharmaceutical formulations
and is generally regarded as an essentially nonirritant and
nontoxic material when used as an excipient.
storage
Polyvinyl acetate phthalate should be stored in airtight containers. It
is relatively stable to temperature and humidity, and does not age,
giving predictable release profiles even after prolonged storage.
At high temperature and humidity, polyvinyl acetate phthalate
undergoes less hydrolysis than other commonly used enteric coating
polymers. In aqueous colloidal dispersions of polyvinyl acetate
phthalate, the formation of free phthalic acid through hydrolysis
was found to adversely affect physical stability.
Following storage at room temperature for 9 months, capsules
coated with a commercial polyvinyl acetate phthalate formulation
(Coateric) were found to retain gastroresistant properties and
showed no apparent physical change; however, a delayed drug
dissolution profile was observed after storage. Storage at 37°C, or
37°C and 80% relative humidity, for 3 months resulted in capsules
having an unsatisfactory appearance.
Incompatibilities
Polyvinyl acetate phthalate reacts with povidone to form an
insoluble complex that precipitates out of solution;benzocaine
is also incompatible with polyvinyl acetate phthalate.Erythromycin
disperses in polyvinyl acetate phthalate and has been shown
to be physically stable while omeprazole exists in the amorphous
form in polyvinyl acetate phthalate coatings with no evidence of
interaction.
Regulatory Status
Included in the FDA Inactive Ingredients Database (sustainedaction
oral tablet). Included in nonparenteral medicines (enteric
coated tablets; in printing ink formulations used for oral tablets and
capsules) licensed in Europe. Included in the Canadian List of
Acceptable Non-medicinal Ingredients.
