Antimicrobial Effectiveness Test (AET) – USP <51>

Nonsterile dosage forms of drugs typically have preservatives added to them in order to protect them from microbial contamination. The Antimicrobial Effectiveness Test (AET) is performed to gauge the performance of those preservatives. Microbes can be inadvertently introduced into a product during manufacturing or during repeated use by consumers. The AET helps assure that the preservative system is robust enough to prevent growth of these microbes.

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.

Antimicrobial Effectiveness Testing (AET) Procedure

AET Growth Promotion and Suitability

USP <51> and EP 5.1.3 recommend conducting a suitability/validation of Recovery Method to determine the ability of the routine testing procedure to identify challenge microorganisms in the presence of the product. If the product shows antimicrobial properties, the ability of media used in this procedure to promote microbial growth must be established. Neutralizers may need to be added to offset these properties.

AET Routine Test

To evaluate the antimicrobial effectiveness of a product, the product is inoculated with a prescribed quantity of specified microorganisms.  The common five USP AET test organisms are C. Albicans, S. Aureus, E. Coli, P. aeruginosa, and A. brasiliensis.  Client isolates or other target organisms can also be used.   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.

Compendial Product Categories

The log reduction required is dependent on the category of the product.  For antimicrobial effectiveness testing, products are grouped into four categories.

Category 1 – Injections, other parenterals including emulsions, otic products, sterile nasal products, and other ophthalmic products made with aqueous bases or vehicles.

Category 2 – Topically used products made with aqueous bases or vehicles; non-sterile nasal products and emulsions, including those applied to mucous membranes.

Category 3 –  Oral products other than antacids, made with aqueous bases or vehicles.

Category 4 – Antacids made with an aqueous base.

Available Antimicrobial Effectiveness Testing (AET) Services

  • AET Suitability of Recovery Method
  • USP <51> (Category 1,2,3, and 4 Products)
  • EP/BP (Parenterals, Opthalmic, Topicals, and Oral Preparations)
  • Custom Studies

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