growth effectively throughout its intended shelf life.

2. Scope

This SOP applies to pharmaceutical formulations containing antimicrobial preservatives (e.g., ophthalmic, nasal, oral liquids, topical products) tested within the Analytical Method Development (AMD) department.

3. Responsibilities

• Microbiologist/Analytical Scientist: Develops the PET protocol, selects organisms, and performs microbiological analysis.
• Formulation Scientist: Provides product composition, preservative system, and pH/stability constraints.
• Group Leader: Reviews test data and evaluates recovery trends.
• QA Executive: Ensures compliance with pharmacopoeial standards and approves method development reports.

4. Accountability

The Head of Analytical Method Development is accountable for ensuring that preservative efficacy methods are validated and aligned with regulatory requirements before implementation.

5. Procedure

5.1 Organism Selection

1. Include at minimum the following challenge microorganisms:
   • Staphylococcus aureus (ATCC 6538)
   • Pseudomonas aeruginosa (ATCC 9027)
   • Escherichia coli (ATCC 8739)
   • Candida albicans (ATCC 10231)
   • Aspergillus brasiliensis (ATCC 16404)
2. Verify culture purity and viability prior to use.

5.2 Inoculum Preparation

1. Grow each organism in appropriate media under specified conditions (temperature, aeration, time).
2. Harvest culture and adjust concentration to 1.0 × 10⁵ to 1.0 × 10⁶ CFU/mL.
3. Verify inoculum count using serial dilution and plate count method.

5.3 Product Inoculation

1. Inoculate the product with each organism (final concentration: 1.0 × 10⁵ to 1.0 × 10⁶ CFU/mL).
2. Use aseptic techniques to prevent contamination.
3. Prepare triplicates for each organism and sampling point.

5.4 Sampling and Incubation

1. Withdraw samples at Day 0, 7, 14, and 28.
2. Perform neutralization and plate count for each sample.
3. Calculate log reduction at each time point relative to initial count.

5.5 Acceptance Criteria (Based on Pharmacopoeial Guidelines)

1. Refer to USP <51>, Ph. Eur. 5.1.3 or IP for product category-specific log reduction requirements.
2. Typical requirements (Category 1 – Injectables, ophthalmics):
   • Bacteria: ≥2 log reduction at 7 days, no increase thereafter
   • Fungi: No increase from initial

5.6 Method Verification

1. Conduct recovery validation using preservative neutralizers (e.g., polysorbate 80, lecithin).
2. Demonstrate neutralizer effectiveness for each microorganism.
3. Include verification results in Annexure-2.

6. Abbreviations

• PET: Preservative Efficacy Test
• CFU: Colony Forming Units
• USP: United States Pharmacopeia
• Ph. Eur.: European Pharmacopoeia
• IP: Indian Pharmacopoeia

7. Documents

1. Preservative Efficacy Method Development Sheet – Annexure-1
2. Neutralizer Effectiveness Verification – Annexure-2
3. Organism Challenge Summary and Log Reduction Table – Annexure-3

8. References

• USP <51> Antimicrobial Effectiveness Testing
• Ph. Eur. 5.1.3 Efficacy of Antimicrobial Preservation
• ICH Q6A: Specifications

9. SOP Version

Version: 2.0

10. Approval Section

	Prepared By	Checked By	Approved By
Signature
Date
Name	Dr. Aarti Nair	Rajan Shinde	Sunita Reddy
Designation	Senior Microbiologist	QA Reviewer	Head – AMD
Department	Analytical Method Development	QA	Analytical Method Development

11. Annexures

Annexure-1: Preservative Efficacy Method Development Sheet

Product	Preservative	Media	Inoculation Date	Sampling Days
Nasal Spray	Benzalkonium Chloride	TSB/SDA	01/05/2025	0, 7, 14, 28

Annexure-2: Neutralizer Effectiveness Verification

Organism	Neutralizer	Recovery (%)	Status
S. aureus	Lecithin + Polysorbate 80	99.8	Pass

Annexure-3: Log Reduction Summary

Organism	Initial (log CFU)	Day 7	Day 14	Day 28	Result
P. aeruginosa	5.5	2.2	<1	<1	Pass

Revision History:

Revision Date	Revision No.	Details	Reason	Approved By
21/05/2025	2.0	Included neutralizer validation and expanded fungal timepoints	Annual SOP Review	Sunita Reddy
15/05/2022	1.0	Initial SOP Release	New SOP	QA Head