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TEST METHOD
Antimicrobial Effectiveness Testing
USP <51> Antimicrobial Effectiveness Testing is a United States Pharmacopeia standard used to evaluate the effectiveness of antimicrobial preservatives in pharmaceutical and cosmetic products. The test measures microbial reduction over time against specified bacteria, yeast, and mold, with results reported as log reduction at defined intervals.
The infographic below provides a brief overview of the USP <51> test method.
Understanding USP <51> Testing
Application areas
USP <51> is applicable to pharmaceutical products that contain antimicrobial preservatives and require evaluation of preservative effectiveness.
Typical applications include:
- Aqueous pharmaceutical preparations
- Topical pharmaceutical products
- Oral pharmaceutical products
- Ophthalmic products
- Other preserved pharmaceutical preparations
The applicable USP <51> acceptance criteria depend on the product category being tested.
Test Microorganisms
USP <51> uses standardized challenge microorganisms representing different groups of microorganisms.
The test panel includes:
- Bacteria: Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa
- Yeast: Candida albicans
- Mold: Aspergillus brasiliensis
These microorganisms are used to assess the preservative system against representative bacterial, yeast, and mold challenges.
Test Protocol
Step 1: Prepare the Test Microorganisms
Standardized cultures of the specified microorganisms are prepared for testing.
Step 2: Inoculate the Product
The product is inoculated with the required microorganisms.
Step 3: Incubate Under Controlled Conditions
The inoculated product is maintained under the specified test conditions.
Step 4: Sample and Enumerate Microorganisms
Samples are collected at defined time points, and surviving microorganisms are recovered and enumerated.
Step 5: Evaluate the Results
The changes in microbial counts are evaluated against the applicable USP <51> acceptance criteria.
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