Methodological validation of microbial limit tests for high-viscosity and common pharmaceutical excipients

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Xi Wang1, Yuying Zhao2, Jing Wang3

  • 1Yunnan Institute for Food and Drug Control, China; Ministry of Industry and Information Technology Industrial Technology Basic Public Service Platform, Kunming, China.

Journal of Microbiological Methods
|April 5, 2026
PubMed

Insights

This study developed and validated microbial limit testing methods for challenging high-viscosity pharmaceutical excipients, ensuring product safety and quality. These new protocols address limitations in current standards for pharmaceutical excipient testing.

Area of Science:

  • Pharmaceutical Science
  • Microbiology
  • Analytical Chemistry

Background:

  • Microbial contamination in pharmaceutical excipients is a major cause of finished product failure.
  • High-viscosity excipients pose significant challenges to standard microbial limit testing due to properties like hygroscopicity and agglomeration.
  • Existing compendial methods often lack specific protocols for these difficult-to-test excipients.

Purpose of the Study:

  • To establish and validate robust microbial limit testing protocols for nine specific pharmaceutical excipients, including four high-viscosity types.
  • To address the analytical challenges presented by high-viscosity excipients in microbial testing.
  • To enhance the reliability and applicability of microbial limit testing for pharmaceutical excipients according to Chinese Pharmacopoeia (ChP) General Principles.

Main Methods:

  • Developed and validated microbial limit testing protocols adhering to ChP General Principles.
  • Performed method suitability testing with recovery rates between 0.5 and 2.0.
  • Validated microbial enumeration for Total Aerobic Microbial Count (TAMC) and Total Yeast and Mold Count (TYMC) using specified microorganisms.
  • Validated methods for specified microorganisms like Escherichia coli and Salmonella.

Main Results:

  • Validated protocols demonstrated method suitability with acceptable recovery rates for all tested excipients.
  • Successful enumeration of TAMC and TYMC was achieved using representative microbial strains.
  • Validated methods confirmed the growth of test bacteria, indicating effectiveness and feasibility.
  • The study identified and addressed gaps in current compendial standards for specific excipients.

Conclusions:

  • The validated microbial limit testing protocols are robust and suitable for high-viscosity and other challenging pharmaceutical excipients.
  • These methods provide a practical solution to technical bottlenecks in pharmaceutical excipient testing.
  • The findings support enhanced regulatory oversight and quality assurance in pharmaceutical manufacturing, particularly in the Yunnan Province.
Keywords:
High-viscosity pharmaceutical excipientsMicrobial controlMicrobial limit testRecovery recoveryWater activity

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