HealthFebruary 09, 2017

Personnel sampling: design and implementation of media fill testing

Media-fill testing is used to measure the aseptic skill of compounding personnel. In order to be effective, the media-fill testing procedure must represent the most complex and challenging procedures performed in a pharmacy during the most stressful conditions possible. A sterile fluid culture media such as soybean casein digest medium (SCDM) or tryptic soy broth is used in place of the steps you would take to make your most complicated compounded sterile preparation (CSP) which is then incubated to test for growth that was introduced during the process. High risk compounders (those who take nonsterile components and make them sterile) start with nonsterile media powder and make it sterile. Commercial media-fill kits often do not mimic the actual procedures performed in a pharmacy and therefore it is strongly recommend that sterile media be purchased in bags, ampules and vials (as well as nonsterile media as powder for high risk compounders) and substituted for the actual components used in the most complex and challenging procedures. For instance, if your pharmacy uses nonsterile bulk API to make an aliquot bag off of which you then draw patient-specific CSPs, then perhaps that would be an opportunity for a media-fill.

How many media fill units should be made during aseptic testing?

Chapter <797> currently does not specify a specific number of media-fill units that should be made at each testing instance. We strongly recommend that at least 3 units be produced by each compounding staff member at each media-fill testing occurrence. It is easier to do something correctly once, than it is to do it some predetermined number of times.

When are facilities required to test the aseptic work skills of their compounders?

At the time of this writing media-fill testing of aseptic work skills are evaluated through media-fill testing at least:

  • Before preparing compounded sterile preparations (CSPs) which means all new employees or when you begin a media-fill testing process if you haven't already
  • Annually for pharmacies performing low and medium risk level compounding
  • Semiannually for pharmacies performing high risk level compounding

Media-fill testing must be performed under the most stressful conditions possible. Instead of performing media-fill testing at the beginning of shift when staff are fresh and the environment is cleanest, media-fill testing should be performed at the end of a shift when operators are fatigued and the engineering controls have been stressed through use during the day.

How often are compounding facilities required to test aseptic work skills?

It is possible that requirements for media-fill testing may increase in frequency in future versions of Chapter <797>.  It might be a good idea to have new staff perform the media-fill test for 3 consecutive days (e.g., 3 units x 3 days in a row) and then 3 media-fill units at specified intervals thereafter but at least at the time intervals specified in the chapter.

Is it reasonable to use sterile water or saline when developing a media fill procedure?

When developing a media-fill procedure, do not add sterile water or saline (except when following manufacturer instructions using powder, nonsterile media when simulating bulk API to make a 3% solution). Use a vial of media to simulate the diluent you might add to a component. Diluting the media with sterile water, will render it too dilute to support microbial growth.

I've heard of double-strength media. Does that allow me to use water to dilute it because it's double-strength?

When using double-strength media, your facility should have a properly accredited, licensed and registered microbiology lab perform growth promotion (according to USP 71) of the media-fill bags produced when following the manufacturer's instructions. Don't be fooled into thinking that adding water is acceptable because the broth is called "double-strength." Double-strength media has different ingredients but is not to be construed as a "media concentrate" to which water can be added.  Doing so may render the media incapable of supporting growth. All media is a 3% solution with every specific compendial standards (see USP Chapter <71>).

Can process verification also be used to fulfill a staff member's aseptic skill verification?

Media-fill testing can also be used to verify the capability of the compounding environment, specific equipment and processes used to make sterile preparations. This is called "process verification." For instance, if your pharmacy begins to use an automated compounder, you may choose to perform an initial process verification whereby you substitute bags, vials and syringes of media for normal source components and make "parenteral nutrition" using media as the components. This process verification provides evidence of whether the ACD is able to produce sterile parenteral nutrition. Performing process verification is not a requirement of Chapter <797> however performing process verification of new or complex processes is a recommended best practice. If you perform process verification, then the person performing this procedure would, in effect, be verifying their aseptic technique (think of the many aseptic connections this person is making) while they are running the process verification.

At what temperature, and how long, should the final media units be stored?

The final media units must be incubated at 20° to 35° centigrade for 14 days. If two temperatures are used for incubation of media-filled samples, then these filled containers should be incubated for at least 7 days at each temperature preferably starting with the lower temperature followed by the higher temperature.

What does a failed aseptic technique look like?

Failures are indicated by visible turbidity (cloudiness) or "strings" or "clumps" in otherwise clear media in any of the media-fill units on or before 14 days.

Does it matter who reads the media fill units?

Ideally, media-fill units are inspected and "read" by a person other than the person who prepared them. The must be visually inspected on no less than day 7 and the end of day 14, however we strongly recommend that they are read daily.

Do you think that frequency requirements for media-fill testing will increase as they do in the proposed version of Chapter <797>?

It very likely that requirements for media-fill testing will increase in frequency from the current requirements of annually or semiannually. Though the proposed chapter is likely to be changed before becoming final, it is unlikely that the quarterly proposed frequency requirements for media-fill testing will be reduced.  Consider increasing the frequency of media-fill testing at your pharmacy. We strongly recommend that media-fill testing replicates the elements of the most complex CSP made; that the testing is performed at the end of the compounding day or shift; and that 3 media-fill units are produced by each compounding staff member initially and then at on at least a quarterly basis.

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