Media fill validation (Aseptic filling process) in Sterile pharmaceuticals

What is a media fill?

A “media fill” (sometimes known as a “process simulation”) is the performance of an aseptic manufacturing procedure using a sterile microbiological growth medium in place of the drug solution. Microbiological growth medium is used in place of the drug solution during media fills to test whether the aseptic procedures are adequate to prevent contamination during actual drug production.  A media fill is one part of the validation of an aseptic manufacturing process.

What is the media fill designed to evaluate?

The media fill should evaluate the aseptic assembly and operation of the critical (sterile) equipment, qualify the operators and assess their technique, and demonstrate that the environmental controls are adequate to meet the basic requirements necessary to produce a sterile drug by aseptic processing. The media fill does not validate the ability of the filter to sterilize growth media.

What are the steps involved in a media fill?

Design

A media fill should be carefully designed to ensure that the simulation is representative of all the aseptic manipulations performed during production.  These include preparation and assembly of the product containers, transfer of the product containers to the fill area, and all process steps downstream from the “sterilizing filter” up to product release, including packaging into finished product containers. Finished product containers with medium should then be incubated to permit the growth of microbial contamination in any containers. Microbiologically contaminated containers are expected to exhibit observable evidence of microbiological contamination after suitable incubation. The same type and source of containers should be used for media fills as are used in routine production.

Media fills should be conducted in the same locations where the production occurs and employ the broadest scope of possible manipulations that could occur during production. Every aseptic manipulation during production up to the point of finished product release should be included in the media fill.  Because each PET finished product container is to be sampled aseptically prior to release, sample withdrawal and any adjustments should be simulated as well.

The media fill is an experiment and therefore should include controls. These controls are independent of the quality audit of the growth medium (i.e., growth promotion testing).

A positive control for a media fill is a sealed product container of medium that is inoculated with a small number (i.e., less than 10²) of microorganisms. Inoculation of the positive control container should be done in an area separate from the critical manufacturing area. 
To ensure the absence of false positive results, a negative control should be included to demonstrate that the medium was sterile to begin with. A negative control may be prepared by preincubating the medium, or by aseptically transferring medium into a separate suitable sterile container and incubating the control simultaneously with the media fill test containers. The controls should be incubated under the same conditions as the media fill containers. These controls may not need to be repeated when multiple media fills are being done within a week and use the same lot of growth medium.

All steps intended for aseptic manufacturing should be reproduced in the media fill, including sampling and dilution of the final product. All personnel involved in the aseptic manufacture of the drug product should participate in at least one media fill per year. All processing steps that the operator normally performs during aseptic manufacturing should be simulated.

After the final product container is filled and ready for release, it should be incubated in a temperature-controlled incubator. Recommends incubation at 20°– 25°C for the aerobic growth medium, as a practical matter any controlled temperature between 20° and 35°C would work for media fills.  However, the “controlled temperature” should be specified in your procedures and be maintained within a range that does not exceed ±2.5°C. The incubation period of a media fill should be no less than 14 days and the containers should be examined every 2 or 3 days.

All steps in a media fill should be done in the same locations as the drug production steps.

The synthesis box is generally located upstream from the sterilizing filter and is not considered a sterile component or part of the aseptic operations. In such cases, do not include the synthesis unit in the simulations.

Preparation for the Test

Once the media fill procedures are established, all of the components necessary for the simulation should be assembled, including all of the equipment used in the aseptic part of the process. Media to be used in the simulation may be obtained commercially or prepared on site, and should be sterile.

When media are prepared on site, sterilization should be conducted using a validated process such as steam autoclave. Filtration is not recommended to sterilize the growth medium.

How do I choose the growth medium?

The most commonly used growth medium is soybean casein digest medium (SCDM), which is commercially available under various names such as Trypticase Soy Broth.

Medium from a qualified commercial vendor may be used by multiple PET facilities for media fills. Shipping, storage, preparation, and handling procedures should be carefully designed, documented, and followed to ensure media integrity and stability. Commercially prepared media should be used within the label’s shelf life and stored according to the label’s recommendations.

How often should a media fill be performed?

To initially qualify an aseptic process at a specific facility, three media fills should be conducted on three separate days at that facility using the specific production process that is being qualified.Additionally, media fills should be conducted whenever significant changes are made to the aseptic process (e.g., changes in personnel, components, or equipment) and whenever there is evidence of a failure to maintain product sterility. Media fills performed to validate an aseptic process at a specific facility should be done by an operator who previously has been trained and qualified in aseptic techniques (e.g., proper gowning, disinfection practices, handling sterile materials).

Media Used for Media fill:

SCDM should be sterile (confirmed by incubating samples for 7 days at a defined controlled temperature), pH 7.3 (±0.2), and able to permit growth of selected aerobic species (e.g., Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa). For media fills, use of only one species of bacteria is necessary once a media vendor is qualified. Media qualification programs should periodically verify the full COA and growth promotion capability to ensure continuing vendor reliability.

What is growth promotion testing? How is it used in PET production?

A growth promotion test ensures that the medium used in the media fill will support the growth of contaminating microorganisms. This is an essential control for media fills because the desired test result is “no growth” and only by demonstrating the medium’s ability to support microbial growth can the negative result be relied upon. Growth promotion testing should be performed on the growth medium used in media fills.  This may be performed by inoculating a portion of the batch with a small number (≤102) of microorganisms to confirm that the medium supports growth.
When the medium is prepared “in-house” (at the site of the PET drug manufacture), a growth promotion test should be performed for each batch of medium prepared. Medium should be prepared using autoclave sterilization processing and not by sterilizing filtration.
A “ready to use” liquid medium supplied from a commercial vendor should be confirmed as suitable by growth promotion and other testing to confirm that it meets specifications and conforms to its COA. Once a supplier has been demonstrated to provide consistently suitable medium, the COA and positive control will suffice to establish the medium’s suitability for use in media fills (the positive control will be used in lieu of demonstrating growth promotion potential).

What is the difference between a growth promotion test and a positive control?

Growth promotion testing confirms the medium’s ability to support growth. Growth promotion testing is commonly done before using the medium in an experiment. A positive control tests the ability of the test method to result in a positive outcome and is commonly done concurrently with an experiment.
Media fill positive control shows that the medium in the drug product container will support growth after exposure to the filling process.

When do I use a positive control?

A positive control is needed for each media fill that is performed using a single batch of medium. As stated previously, a positive control in the media fill may also serve as the growth promotion test of the medium. When performing a media fill, the positive control test may be done simultaneously with the media fill by inoculating a vial of medium from the same batch used for the media fill. It is also permissible to perform a positive control at the end (after incubation) of a media fill by inoculating an uncontaminated media fill test container and returning it for additional incubation. Inoculation of the positive control container should be done in an area separate from the critical manufacturing area.

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