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Efficacy of Antimicrobial Preservation

AET suspension test for preservative efficacy

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The antimicrobial efficacy test (AET) is a suspension test for microbial kill.  That is to say, a controlled inoculum of the challenge organism(s) is placed in suspension with the sample to be tested, and then the number of survivors determined at different time points. The test is done to control the effect of antimicrobial preservatives in non-sterile drugs in multiple dose packaging. The test is performed according to Ph Eur 5.1.3 (Efficacy of Antimicrobial Preservation) and USP (Antimicrobial Effectiveness Testing) or testing adjusted to special packaging. The different microorganisms to be used are described in the Pharmacopoeia.

AET is described for a number of different product categories,. For example: 
  • Parental drugs and preparations for eyes, uterus and breast tissue
  • Topical preparations
  • Oral and rectal preparations

It is recommended to perform AET at the end of the shelf life of the product, in relation to a change of the material in the primary packaging or if the formula of the preservative in the product is changed.

Analysis result, response time

Incubation time is regulated by the current pharmacopeia and will therefore vary depending on product type. Before analysis can start the microorganisms needs to be prepared by cultivation. Sampling is then performed at specified time points with the last sampling being after 28 days of incubation. Normally the total analysis time including report out is 35-40 business days.