Sterility Testing

Dear All,

I want to do sterility test of Gel product. It is very viscous so that it is not use in membrane filtration method. When i apply direct inoculation method, it created precipitation in both medium SCDM and FTGM.
Please help me regarding this Gel product sterility test. Anybody have solution for the same, please share me your experience.


1 Like

Gels are usually water soluble. Have you tried to aseptically dissolve you sample in suitable diluent prior to membrane filtration?
Also, Ph.Eur. states that if your sample renders the media turbid, you are allowed to leave the media for the two week incubation period, then transfer part of the media to a fresh portion of media and incubate for another five days. I’m not sure which pharmacopeia you have to follow, but check the sterility testing monograph

Thanks for your valuable reply
Our Gel sample is not soluble in water.
As per your reply , we refer the EP, it is possible to incubate 14 days and then take some sample from that and again incubation. It is validate or not?

I would say yes, if validated in this manner. Be sure to dilute your control vessel without product as well. BTW what is the solubility of your product? What component in your matrix is causing the problem?
Have you considered heating your product in a diluent to max 40 degrees C? Would your product be soluble in isopropyl myristate (again with heating to max 40 degrees C if necessary)?

Hi, good morning.

Our product contain Ethyl cellulose, ethyl alcohol and tangsten. these all are in-soluble in water. As you mention above method inoculation after 14 days, We have also done 1 ml media transfer from 14 days incubated media to fresh media. There was also precipitate observed.
If you have alternate method for the same, please help us.


we are waiting for your positive reply…

*Pre-dilute your sample (min 200 mg solids/container) with suitable solvent/emulsifier such as tween 80. Perform direct inoculation test using concentrated media. for instance, to 300 ml of diluted sample, add 100 ml of 4x concentrated media. This way you can sample a larger volume of your dilution. After 14 days transfer 1 ml to fresh media and incubate according to pharmacopeia. In this you accept that your final sample may not be completely clear. Create a reference sample to compare your test sample to when reading the results of your test (sterilize test sample from previous passed test) and test your technicians in this. Not ideal, I know.
*Try an ATP based test such as Milliflex rapid sterility. But this might involve a considerable investment in time and money. Aside from it being a destructive test (identification of micro organisms difficult to impossible). It might help contacting them, they might know a solution to your problem.

thanks for your reply…
I am not getting first three line of your reply. Can you elaborate it ?
For the better understanding…

thanks in advance…

According to Ph.Eur. direct inoculation technique may also be performed by adding your (in this case diluted) product directly to a volume of concentrated medium.
Example: Ph.Eur. prescribes a minimum of 200 mg of solid sample, the batch size implies a number of 10 containers. 200 mg/container x 10 containers = 2000 mg of sample.
This is aseptically weighed and diluted using for instance 300 mL of sterile diluent. In duplicate of course, since you need two different media.
When using 4x concentrated TSB, aseptically add 100 mL of said medium directly to one of the bottles containing 2000mg sample per 300mL diluted sample. Repeat for 4x concentrated FTM. Add 0.2 um vent filters to allow aeration. Incubate and process the bottles as usual.
You end up with 2 bottles containing 400 mL of sample/medium combination, but the media will be of the composition prescribed in the pharmacopeia, since you diluted it 4 times.

Dear all,
I have following question regarding sterility test in sterile API
(1) For cytotoxic sterile API how much quantity we require to perform sterility test?(I don’t get clarity from USP 71, table-2,3 )
(2) If batch size is extremely less then how much minimum quantity we need to consider for sterility testing?