Standard Operating Procedure for Filter Integrity Testing in Bioreactor Operations for Biosimilars

Department	Biosimilars
SOP No.	SOP/BS/091/2025
Supersedes	SOP/BS/091/2022
Page No.	Page 1 of 10
Issue Date	04/05/2025
Effective Date	06/05/2025
Review Date	04/05/2026

1. Purpose

To establish a standard procedure for performing integrity testing of sterile filters used in bioreactor operations for biosimilar manufacturing. This ensures the filter maintains microbial retention capacity and complies with GMP requirements.

2. Scope

This SOP applies to all in-line and offline filters (vent filters, liquid filters, sterilizing-grade filters) used in upstream and downstream biosimilar processes before and after filtration steps.

3. Responsibilities

• Production Operator: Conduct filter integrity tests and document results.
• QA Executive: Verify test values are within acceptance criteria and approve filter usage.
• Engineering: Maintain integrity testers and calibrate testing equipment regularly.

4. Accountability

The Production Manager is accountable for ensuring that filters pass integrity testing before product contact and that failed filters are investigated per deviation procedures.

5. Procedure

5.1 Pre-Test Requirements

1. Ensure filters are installed correctly and wetted with appropriate fluid (e.g., WFI or buffer).
2. Verify test equipment calibration status and that tubing connections are leak-free.

5.2 Bubble Point Test

1. Connect integrity tester to filter housing.
2. Apply increasing pressure to wetted filter membrane using compressed air/nitrogen.
3. Monitor for sudden rise in air flow, indicating the largest pore has emptied.
4. Record the bubble point pressure; it must be above manufacturer’s minimum specification (e.g., ≥3.5 bar for 0.2 µm PES filter).

5.3 Diffusion Test

1. Maintain constant pressure below the bubble point (e.g., 2.5 bar).
2. Measure the rate of diffusive air flow across the membrane.
3. Compare observed flow with filter specifications (e.g., ≤15 mL/min).

5.4 Forward Flow Test (if applicable)

1. For double-layer filters, use forward flow testing using dedicated integrity tester.
2. Ensure flow rate remains within validated limits.

5.5 Post-Use Testing

1. Repeat the integrity test after product filtration to confirm no damage occurred.
2. Label filters with test status and retain record in Annexure-1.

5.6 Action on Failure

1. If the filter fails any integrity test:
   • Quarantine filtered product
   • Initiate deviation investigation
   • Retest with back-up filter, if available

6. Abbreviations

• WFI: Water for Injection
• QA: Quality Assurance
• PES: Polyethersulfone
• µm: Micrometer

7. Documents

1. Filter Integrity Test Log – Annexure-1

8. References

• USP <1207> – Sterile Package Integrity Evaluation
• WHO GMP Annex 2 – Guidelines for Biotech Products

9. SOP Version

Version: 2.0

10. Approval Section

	Prepared By	Checked By	Approved By
Signature
Date
Name
Designation
Department

11. Annexures

Annexure-1: Filter Integrity Test Log

Date	Batch No.	Filter ID	Filter Type	Test Type	Result	Test Pressure (bar)	Remarks	Operator
04/05/2025	BS-091-B01	FT-PES-32	0.2 µm PES	Bubble Point	Pass	3.7	Within specs	Ajay Verma

Revision History:

Revision Date	Revision No.	Revision Details	Reason for Revision	Approved By
04/05/2025	2.0	Included post-use testing and failure handling procedure	Compliance with current regulatory expectations