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Antimicrobial Effectiveness Test (AET)

Nonsterile dosage forms of drugs typically have preservatives added to them in order to protect them from microbial contamination. Microbes can be introduced inadvertently during manufacturing, or during the continual use of a product.

The USP 51 antimicrobial effectiveness test, also known as the preservative efficacy test, is performed to determine if the chosen preservative is appropriate for a product formulation. It is also carried out as part of a stability study, to ascertain whether a preservative system is still effective up to the expiration date of a product. Testing is performed according to compendial requirements in both USP <51> and EP 5.1.3.

To evaluate the antimicrobial effectiveness of a product, the product is inoculated with a prescribed quantity of specified microorganisms. The effectiveness of the preservative is evaluated by comparing the initial level of microorganisms to the test sample at various time intervals over a period of 28 days at a specified temperature. Reduction of microorganisms is calculated logarithmically. Included in this category of testing is AET validation as well as zone of inhibition testing.

Time Kill Test

The Time Kill Test, or Time Kill analysis, is carried out to evaluate an antimicrobial test material or disinfectant and assesses the in vitro reduction of a microbial population of test organisms after exposure to a test material.

The Time Kill Analysis measures the change in a population of microorganisms within a specified sampling time when after exposure to antimicrobial test materials in vitro. The test article or its dilution is brought into contact with a known population of microorganisms for a specified period of time at a specified temperature. The test article is then neutralized at the target sampling time and the surviving organisms are enumerated. The percent and/or log10 reduction from either an initial microbial population or test blank is calculated.

Several options for organism selection and growth, inoculum preparation, sampling times and temperatures can be requested. Testing is performed according to
ASTM E 2315-03.

Learn more about the Antimicrobial Effectiveness Test in our Learning Center entry on the AET.

Available AET Services

  • AET Validation
  • USP (Category 1,2,3, and 4 Products)
  • EP/BP (Parenterals, Opthalmic, Topicals, and Oral Preparations)
  • Zone of Inhibition Testing
  • Custom Studies

Time Kill Services

  • Time Kill Analysis
  • Minimum Inhibitory Concentration
  • MBC Testing (Minimum Bactericidal Testing)


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