<51>, EP, and JP guidelines.

2. Scope

This procedure applies to the Analytical Method Development and Microbiology departments engaged in preservative efficacy testing of sterile and non-sterile pharmaceutical dosage forms (e.g., oral liquids, ophthalmics, topical creams, etc.).

3. Responsibilities

• Microbiologist: Prepares microbial cultures, inoculates test samples, and monitors microbial survival.
• Analytical Scientist: Coordinates formulation sampling and supports neutralization validation.
• QA Officer: Reviews data and ensures adherence to test acceptance criteria.
• Head – AMD: Approves AET protocols and ensures harmonization with global pharmacopeial requirements.

4. Accountability

The Head of Analytical Method Development is accountable for ensuring that the developed AET method is scientifically justified, validated, and compliant with applicable regulations.

5. Procedure

5.1 Selection of Challenge Microorganisms

1. Use ATCC-certified cultures:
   • Staphylococcus aureus (ATCC 6538)
   • Pseudomonas aeruginosa (ATCC 9027)
   • Escherichia coli (ATCC 8739)
   • Candida albicans (ATCC 10231)
   • Aspergillus brasiliensis (ATCC 16404)
2. Maintain cultures on nutrient agar/SDA slants and prepare working suspensions at 10⁵ to 10⁶ CFU/mL.
3. Log culture preparation in Annexure-1: Culture Inoculum Log.

5.2 Sample Preparation and Inoculation

1. Use the final pharmaceutical product without dilution or preservative alteration.
2. Inoculate each test container with a defined volume of microbial suspension to achieve 10⁵–10⁶ CFU/mL final concentration.
3. Mix gently to avoid foaming and allow uniform dispersion.
4. Inoculate positive controls (growth media) and negative controls (uninoculated sample).
5. Log inoculation in Annexure-2: AET Inoculation Record.

5.3 Incubation and Recovery

1. Incubate inoculated samples at 20–25°C and monitor microbial count at:
   • Day 0 (post-inoculation)
   • Day 7
   • Day 14
   • Day 28
2. Perform viable count by serial dilution and plate pour/spread method on appropriate media:
   • Nutrient Agar for bacteria
   • SDA for fungi
3. Document in Annexure-3: AET Microbial Recovery Sheet.

5.4 Acceptance Criteria (USP <51>)

1. Category 1 (Injections, eye drops, etc.):
   • ≥ 1.0 log reduction by Day 7 for all microorganisms
   • No increase from initial count at Day 28
2. Category 2 (Topical, oral, nasal):
   • ≥ 2.0 log reduction by Day 14 for bacteria
   • Stable or reduced fungal counts by Day 28

5.5 Neutralization Validation

1. Validate that the preservative does not inhibit microbial recovery after dilution or neutralizer addition (e.g., Dey-Engley Broth).
2. Perform recovery studies with known CFUs and compare to growth control.
3. Document in Annexure-4: Neutralization Validation Log.

5.6 Data Analysis and Reporting

1. Calculate log reductions using:
   
   Log Reduction = log₁₀(Initial CFU) − log₁₀(Recovered CFU)
2. Tabulate microbial reduction data across all time points.
3. Compile results in Annexure-5: AET Summary Report.

6. Abbreviations

• AET: Antimicrobial Effectiveness Testing
• CFU: Colony Forming Unit
• USP: United States Pharmacopeia
• SDA: Sabouraud Dextrose Agar
• SOP: Standard Operating Procedure

7. Documents

1. Culture Inoculum Log – Annexure-1
2. AET Inoculation Record – Annexure-2
3. AET Microbial Recovery Sheet – Annexure-3
4. Neutralization Validation Log – Annexure-4
5. AET Summary Report – Annexure-5

8. References

• USP <51> – Antimicrobial Effectiveness Testing
• EP 5.1.3 – Efficacy of Antimicrobial Preservation
• ICH Q6A – Specifications: Test Procedures

9. SOP Version

Version: 2.0

10. Approval Section

	Prepared By	Checked By	Approved By
Signature
Date
Name
Designation
Department

11. Annexures

Annexure-1: Culture Inoculum Log

Date	Organism	CFU/mL	Prepared By
18/05/2025	C. albicans	1.3 × 106	Sunita Reddy

Annexure-2: AET Inoculation Record

Sample ID	Organism	Inoculum Volume	Initial CFU	Inoculated By
AET-131-01	E. coli	0.5 mL	1.0 × 105	Rajesh Kumar

Annexure-3: AET Microbial Recovery Sheet

Day	Organism	CFU/mL	Log Reduction	Status
7	E. coli	1.8 × 102	2.75	Pass

Annexure-4: Neutralization Validation Log

Organism	Neutralizer	CFU Recovered	Recovery %	Status
S. aureus	D/E Broth	95	95%	Pass

Annexure-5: AET Summary Report

The developed method met USP <51> requirements across all five challenge organisms. Log reductions were within prescribed limits. Method is robust and validated for preservative efficacy testing of topical and oral formulations.

Revision History:

Revision Date	Revision No.	Details	Reason	Approved By
04/05/2025	2.0	Included ICH Q6A and EP references; expanded acceptance criteria	Annual SOP Review