Most sterile manufacturers know what PUPSIT stands for. Far fewer have a program they’d be confident defending under inspector scrutiny.
Here is what regulators expect, how industry has responded, and what you should actually be doing.
Why PUPSIT Exists
The core concern is simple: sterilization damages filters.
Autoclaving, steam-in-place, and gamma irradiation all stress filter membranes. A filter that passes integrity testing before sterilization may not pass after. If that compromised filter is used to sterilize a batch — and the defect goes undetected — the entire batch may be non-sterile. The post-use integrity test, conducted after filtration, would catch the failure. But by then, the product has already passed through a potentially compromised membrane.
PUPSIT closes that window. It confirms the filter is intact at the precise moment it matters: before product contact.
What Regulators Expect
FDA’s Guidance for Industry on Sterile Drug Products Produced by Aseptic Processing (2004) supports pre-use integrity testing as a best practice, and FDA 483 observations and Warning Letters increasingly cite absent or inadequate PUPSIT programs. While FDA guidance predates the Annex 1 revision, the agency’s inspection posture has aligned with the EU position.
The revised EU GMP Annex 1, effective September 2023, is the most explicit global guidance on PUPSIT. It requires that sterilizing-grade filters used for final sterile filtration be integrity tested, with documented justification if this is not performed (European Commission, 2022, §8.87).
The keyword is justification — not exemption. The default expectation is PUPSIT. Deviation requires a documented, risk-based rationale.
PIC/S PE 009-16 and WHO Technical Report Series No. 961 (GMP for sterile pharmaceutical products) both align with the EU framework, emphasizing that filter integrity must be confirmed before use in sterile operations (PIC/S, 2019; WHO, 2011). For manufacturers supplying global markets, PUPSIT is effectively a universal expectation.
The regulatory intent, across all bodies:
Integrity testing after sterilization is not bureaucratic formality. It is a sterility assurance control. Regulators view the absence of PUPSIT — without robust justification — as a gap in contamination control strategy.
How Industry Has Responded:
The ISPE Baseline Guide for Sterile Product Manufacturing and the associated contamination control guidance address PUPSIT as part of a layered sterility assurance strategy. ISPE frames it within the broader Contamination Control Strategy (CCS) framework required by Annex 1 — PUPSIT is one control among many, but its absence must be accounted for in the overall risk picture (ISPE, 2022).
PDA Technical Report No. 26 (Revised 2008) on Sterilizing Filtration of Liquids remains the foundational industry reference. It provides detailed guidance on integrity test methods, acceptance criteria, and the rationale for pre- and post-use testing. TR 26 explicitly acknowledges that pre-use testing is the more protective approach and should be the default where feasible (PDA, 2008).
BioPhorum’s contamination control publications and their Drug Substance filtration guidance have addressed PUPSIT implementation challenges directly, particularly for biologic manufacturers dealing with protein-containing products where wetting agents and flush volumes create practical complexity (BioPhorum, 2021).
The industry consensus:
Pre-use testing is the expectation. Practical challenges do not eliminate the requirement — they require engineered solutions or documented risk-managed alternatives.
Practical Application:
Most manufacturers implement PUPSIT using one of two approaches:
- Integrity tester integrated into the filter housing or skid, with automated test execution post-SIP/post-autoclave and before product flow is initiated. This is the cleanest solution and the most defensible.
- Manual testing using a portable integrity tester, with the test performed in the clean room environment after sterilization. This works, but introduces more human interaction and requires robust procedural controls.
The key technical requirement: the test must be performed after the filter is in its final installed state — in the same housing, in the same configuration, in the same environment it will be used for filtration. Testing a filter on the bench, then installing it, does not satisfy the intent.
Typical Challenges:
High-concentration biologics can cause wetting issues, where product residue from a PUPSIT flush affects downstream protein concentration or bioburden. This is the most frequently cited reason manufacturers attempt to justify skipping PUPSIT. It requires careful flush validation, not avoidance.
Pre-assembled, gamma-irradiated single-use filter assemblies present a genuine challenge. Testing before use in a closed system requires integrity test connections to be built into the assembly design. Some suppliers offer this; not all do. This is increasingly a procurement and design-phase issue, not just an operations issue.
Some processes have narrow filtration windows. Testing adds time. This is real but solvable through process design, not by eliminating the test.
Frequent Inspection Observations
- PUPSIT justifications that are generic rather than product-specific
- Risk assessments that conclude “impractical” without quantifying the actual risk.
- Procedures that describe PUPSIT but don’t clearly define the test window (after sterilization, before product contact)
- Integrity tester qualification gaps — instruments used for PUPSIT must be qualified like any other critical instrument
- Lack of PUPSIT in the Contamination Control Strategy document, even when it’s performed operationally
What Good Looks Like
Strong programs share three characteristics:
- PUPSIT is the default. It is performed for all sterile filtration steps unless a specific, documented, product-level risk assessment justifies otherwise.
- The justification is real. When PUPSIT is not performed, the file contains a product-specific risk assessment, reviewed by QA, that identifies the specific hazard, evaluates compensating controls, and documents residual risk acceptance by senior management.
- The integrity tester is qualified. Instruments are calibrated, qualified, and subject to periodic performance verification. Test parameters are product- and filter-specific, not pulled from a generic template.
Key Takeaways:
Strong programs share three characteristics:
- Default to PUPSIT. Annex 1 (2022) sets it as the expectation, not the exception. Build it into process design from the start.
- Justify with specifics, not generalities. “Impractical for our product” is not a risk assessment. Name the hazard, quantify the risk, identify compensating controls.
- Integrate testing into the system. Manual testing with a portable instrument is acceptable but requires tight procedural control. Integrated automated testing is more robust and more defensible.
- Address single-use assemblies proactively. Require integrity test ports in single-use filter specifications. This is a supplier qualification issue before it becomes an inspection issue.
- Update your CCS. If PUPSIT is not explicitly addressed in your Contamination Control Strategy document — whether you perform it or justify not performing it — fix that now.
References:
- BioPhorum. (2021). Drug substance filtration: Guidance on PUPSIT and contamination control for biologic manufacturing. BioPhorum Operations Group.
- European Commission. (2022). EU Guidelines for Good Manufacturing Practice for Medicinal Products for Human and Veterinary Use, Annex 1: Manufacture of sterile medicinal products. European Commission.
- International Council for Harmonisation. (2023). ICH Q9(R1): Quality risk management. ICH.
- International Society for Pharmaceutical Engineering. (2022). ISPE baseline guide: Sterile product manufacturing (3rd ed.). ISPE.
- Parenteral Drug Association. (2008). PDA Technical Report No. 26 (Revised 2008): Sterilizing filtration of liquids. PDA.
- Pharmaceutical Inspection Co-operation Scheme. (2019). PIC/S PE 009-16: Guide to good manufacturing practice for medicinal products, Annex 1. PIC/S.
- U.S. Food and Drug Administration. (2004). Guidance for industry: Sterile drug products produced by aseptic processing — Current good manufacturing practice. FDA.
- World Health Organization. (2011). WHO Technical Report Series No. 961, Annex 6: WHO good manufacturing practices for sterile pharmaceutical products. WHO.
Strong programs share three characteristics:
- Default to PUPSIT. Annex 1 (2022) sets it as the expectation, not the exception. Build it into process design from the start.
- Justify with specifics, not generalities. “Impractical for our product” is not a risk assessment. Name the hazard, quantify the risk, identify compensating controls.
- Integrate testing into the system. Manual testing with a portable instrument is acceptable but requires tight procedural control. Integrated automated testing is more robust and more defensible.
- Address single-use assemblies proactively. Require integrity test ports in single-use filter specifications. This is a supplier qualification issue before it becomes an inspection issue.
- Update your CCS. If PUPSIT is not explicitly addressed in your Contamination Control Strategy document — whether you perform it or justify not performing it — fix that now.
The author is a senior pharmaceutical quality, regulatory affairs, and manufacturing consultant with more than 20 years of experience in GMP compliance, sterile manufacturing, contamination control, and validation.