Microbial Retention Studies

Our microbial retention studies qualify the filter under test to repeatedly produce a sterile filtrate with the drug product under simulated worst case process conditions in accordance to:

  • USFDA CDER guidance document on Sterile Drug Products Produced by Aseptic Processing
  • PDA Technical Report No. 26, Revised 2008 on Sterilizing Filtration of Liquids

This involves establishing the viability of the test organism in the drug product and testing the filter for bacterial retention test under simulated process conditions.


Establishes whether the drug product is bactericidal to the test organism under simulated process conditions of temperature and contact time. This in turn helps establish the test methodology for the bacterial challenge/retention studies.


The drug product or simulant is inoculated with the challenge organism at a concentration >1x107 viable organisms/cm2 of filter area and the test is performed on filters from three different lots, with at least one having a pre-filtration physical integrity test value at/or near the filter manufacturer specified limit.

  • For non-bactericidal drug products the filter is challenged with the test organism suspended in drug product.
  • For bactericidal products viability studies are carried out with modified formulation, modified process conditions, or in product surrogate. In such cases filter preconditioning with the product under worst case process conditions is carried out followed by bacterial challenge test with modified formulation/process under which test organism viability has been established.