Antimicrobial Effectiveness Testing (AET) or Preservative Effectiveness Testing is an essential quality control procedure for sterile and nonsterile aqueous drug products. It is performed to determine the effectiveness of the antimicrobial preservatives incorporated within the formula to retard the growth of microorganisms that are potentially brought into the product by manufacturing, packaging, or repeated use.

At Chromak Research, a certified contract testing laboratory, we conduct USP <51> AET for pharmaceutical and healthcare products such as multi-dose injectable products, oral solutions, topical products, and other preserved

dosage forms.Our scientists make sure that your product meets the current United States Pharmacopeia (USP) requirements, with accurate, validated results for regulatory filing and product release.

What is USP <51> Antimicrobial Effectiveness Testing?

According to USP <51>, Antimicrobial Effectiveness Testing is the test applied to find out whether the antimicrobial preservative system in a pharmaceutical drug product is capable of resisting microbial contamination for its intended shelf life.

The test includes:

Inoculating the product with a predetermined number of microorganisms, i.e., bacteria and fungi.

Monitoring microbial levels during a 28-day testing period.

Log reduction measuring viable microorganism numbers at predefined time points (usually Day 7, 14, and 28).

Assay of whether the preservative system meets the acceptance criteria provided in USP <51> for each microbial strain.

The challenge organisms commonly used are:

  • Staphylococcus aureus
  • Pseudomonas aeruginosa
  • Escherichia coli
  • Candida albicans
  • Aspergillus brasiliensis

These challenge organisms are typical contaminants that can taint product stability and safety if they are not well managed.

Why Antimicrobial Effectiveness Testing is Needed

Preservatives are added in most products to:

  • Prevent contamination with microorganisms under multi-dose usage.

  • Enhance shelf life by being sterility or microbiological integrity assured.

  • Ensure patient safety, especially for nasal and ophthalmic products and injectables.

  • Meet standards such as USP, FDA, and international pharmacopeial standards and requirements.

Preservative ineffectiveness may lead to product recalls, regulatory hold-ups, or end user safety hazards.

Chromak Research AET Capabilities

Here at Chromak Research, we provide robust AET solutions following USP <51> guidelines, accurate and reproducible, and fully compliant. Our solutions include:

  • Multi-dose injectable product AET
  • Oral liquid, topicals, ophthalmics, and nasal sprays AET testing
  • Antimicrobial preservative systems testing in sterile and nonsterile products
  • Complete documentation and regulatory assistance with submission-ready reports

Chromak Research is fully equipped with well-facilitated microbial laboratories and microbiology professionals who have strict aseptic methods and controlled environment procedures to guarantee quality results.

Partner with Chromak Research for USP <51> AET Testing

When you select Chromak Research, you’re investing in a laboratory dedicated to regulatory compliance, scientific excellence, and customer-focused service. We understand the importance of preservative efficacy to ensure product safety on a continuous basis—and we can assist you in meeting your quality and regulatory requirements.

Whether you’re formulating a new product or testing a current product, our USP <51> antimicrobial effectiveness testing can assist you in validating that your preservative system functions well over the long term.

Contact us today to learn more about our AET services, request a quote, or discuss how we can support your next product testing project.