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Evaluating Materials for Container Closure Systems for Medical Products

Materials include glass, metal, plastic and rubber, each of which has advantages and disadvantages. Factors such as the physical performance, the nature of supply and the chemical compatibility of the material must be considered.

Emilia Hevelke prepares samples for testing in Smithers’ analytical chemistry laboratory in Leatherhead, U.K.
Emilia Hevelke prepares samples for testing in Smithers’ analytical chemistry laboratory in Leatherhead, U.K.

The first step in the selection process is to consider the physical performance of each of the materials. Does the material have the correct barrier properties, such as protection from moisture?

There exist more than 90 generic plastic types with more than 100 sub-generic modified types. Plastics offer a combination of properties not available in other materials. Some of these include:

  • Transparency—comparable with glass
  • Good chemical resistance
  • Good barrier properties—gas/liquid permeation resistance
  • Can be sterilized
  • Ability to be tinted in many different colors

The physical performance of plastics makes them prevalent in the pharmaceutical industry. In addition, they feature low unit costs, the ability to be processed and many can be recycled.

Another consideration is the ability of the material to be manufactured and molded with the correct tolerances. Metered dose inhalers, for example, have multiple parts that require manufacturing to tight tolerances to enable the patient to receive the correct dose of medication.

The nature of the material is especially important when considering the propensity of the material to shed particulates. In the last 12 months, there have been numerous product recalls due to potential particulate matter hazards.

Rubber

For rubber materials, as with plastics, there are a huge range of different types and suppliers, each offering a diverse range of properties. The same factors that are considered for plastics need to be reviewed for rubber. In general, rubber materials are more complex than plastics and typically include more processing steps and additives than plastics. The base elastomer will have fillers, pigments and a curing system added. In one example, the rubber will then go through processing to form a sheet from which gaskets can be cut out.

Glass

Glass could be viewed as an ideal material in certain circumstances. It is transparent, has excellent barrier properties and is easily sterilized. However, there have been medical products recalled due to glass delamination, which occurs when small (visible/sub-visible) particles of glass end up in the drug product. This typically happens with product formulations that have a basic pH (>7.0); that contain citrate buffers; have a high ionic strength (>100 mM NaCl); and/or are stored in a certain vial type (tubing) or vial size (>5 mL).

Metals

Metals are generally the lowest risk materials both in terms of their physical properties and chemical compatibility. Low risk does not mean no risk though and care should be taken if metals are treated in some way before use, even washing and the presence of surfactants should be considered. Surface treatments and overall oxidation need to be considered for compatibility and stability.

Chemical compatibility

There are two main areas to take into consideration for chemical compatibility of materials for medical products. First, does the active pharmaceutical ingredient (API) interact directly with the material, e.g. as sorption, either adsorption or absorption? This can affect the efficacy of the product by reducing the level of API available for the patient.

While receiving the incorrect dose can be a minor problem, in certain circumstances it can be potentially life-threatening. This is highlighted by a recent product recall of an epinephrine auto-injector that failed to deliver the correct dose. This type of product is used to treat life-threatening anaphylaxis. In this case, there was a physical malfunction of the device and not a chemical interaction. Secondly, can a chemical species migrate from the material used in the container closure system and leach into the product, potentially affecting patient safety?

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