Thermoplastic polymers have been established as packaging
materials for sterile preparations, such as large-volume parenterals, ophthalmic solutions, and, increasingly, small- volume
parenterals. For such use to be acceptable, a thorough understanding of the characteristics, potential problems, and advantages for use must be developed. Three principal problem areas
exist in using these materials:
1. Permeation of vapors and other molecules in either direction through the wall of the plastic container;
2. Leaching of constituents from the plastic into the product; and
3. Sorption (absorption and/or adsorption) of drug molecules or ions on the plastic material.
Permeation, the most extensive problem, may be troublesome
by permitting volatile constituents, water, or specific drug molecules to migrate through the wall of the container to the outside
and, thereby, be lost. This problem has been resolved, for example, by the use of an overwrap in the packaging of IV solutions in
PVC bags to prevent loss of water during storage. Reverse permeation in which oxygen or other molecules may penetrate to the
inside of the container and cause oxidative or other degradation
of susceptible constituents may also occur. Leaching may be a
problem, when certain constituents in the plastic formulation,
such as plasticizers or antioxidants, migrate into the product.
Thus, plastic polymer formulations should have as few additives
as possible, an objective characteristically achievable for most
plastics used for parenteral packaging. Sorption is a problem on
a selective basis, that is, sorption of a few drug molecules occurs
on specific polymers. For example, sorption of insulin and other
proteins, vitamin A acetate, and warfarin sodium has been shown
to occur on PVC bags and tubing, when these drugs were present
as additives in IV admixtures. Table 26-2 gives a brief summary
of some of these compatibility relationships.
One of the principle advantages of using plastic packaging
materials is that they are not breakable, as is glass; also, there
is a substantial weight reduction. The flexible bags of polyvinyl
chloride or select polyolefins, currently in use for large-volume
intravenous fluids, have the added advantage that no air interchange is required; the flexible wall simply collapses as the solution flows out of the bag.
Most plastic materials have the disadvantage of not being
as clear as glass, and, therefore, inspection of the contents is impeded. However, recent technologies have overcome this limitation, evidenced by plastic resins, such as CZ (polycyclopentane,
Daikyo Seiko) and Topas COC (cyclic olefin copolymer, Ticona).
In addition, many of these materials soften or melt under the
conditions of thermal sterilization. However, careful selection of
the plastic used and control of the autoclave cycle has made thermal sterilization of some products possible, large-volume injectables, in particular. Ethylene oxide or radiation sterilization may
be employed for the empty container with subsequent aseptic
filling. However, careful evaluation of the residues from ethylene
oxide or its degradation products and their potential toxic effect
must be undertaken. Investigation is required concerning potential interactions and other problems that may be encountered
when a parenteral product is packaged in plastic.
Future trends in primary packaging for parenterals will continue to see significant growth in the application of plastic vials and syringes and the manufacturing of such packaging by
form- (or blow-) fill-seal technologies. (For further details, see
Chapter 35 (Pharmaceutical Packaging) and the review book
chapter by Vilivalam and DeGrazio.22
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