To meet the EU’s GMP Annex 1 guidelines for the manufacture of sterile medicinal products, pre-use post-sterilization integrity testing (PUPSIT) is a critical process step in your manufacturing operation.
PUPSIT is the process of performing filter integrity testing on sterilizing filters after the sterilization procedure is complete but immediately prior to conducting the sterile filtering of product; it should be performed any time a manufacturing process leverages sterile filtering.
Though there may be misconceptions around the complexity, risks, and regulatory expectations surrounding PUPSIT, its implementation is essential to releasing a product in the EU. Therefore, to ensure compliance with Annex 1 and the regulatory approval of your drug product, familiarize yourself with PUPSIT, including how it works, why it is needed, and strategies to maximize success.
1. Why and How Is PUPSIT Conducted?
PUPSIT verifies that a sterilizing filter is integral and that there is no defect or damage that may have occurred to the filter during transportation, handling, or sterilization. Without PUPSIT, filter defects may go undetected due to the product clogging or masking damage to the filter membrane during processing. This masking or fouling can result in a damaged filter passing post-use integrity testing, which is conducted offline after product filtration is completed.
To conduct PUPSIT, operators wet a filter with water, buffer, or product — a selection dependent on filter and product type as well as filter validation. From there, a separate piece of equipment is connected to the manufacturing line to conduct an automated integrity test of the filter membrane to ensure that it is fully integral prior to sterile filtering. The parameters for the integrity test designate pressure and stabilization time for the automated cycle and are determined via product/process, filter manufacturing criteria, and filter validation. Once the test is complete, operators receive a pressure reading and a pass/fail result for filter integrity.
2. Where Is PUPSIT Required, and What Do Regulators Expect?
Though PUPSIT is not required by the U.S. FDA, it is mandated for drugs approved in the EU. According to the EU GMP Annex 1, “The integrity of sterilized filter assembly should be verified by integrity testing before use (PUPSIT) to check for damage and loss of integrity caused by filter preparation prior to use.” Despite the use of the word “should,” EU regulators broadly interpret PUPSIT as an expectation rather than an option.
To determine your sterile filter integrity testing strategy, collaborate with your qualified person (QP) — the EU-mandated professional responsible for certifying that each drug batch meets quality, safety, and GMP standards prior to release — to understand the technical attributes of your product and process as it relates to PUPSIT. If you choose not to conduct PUPSIT, you must execute a thorough risk assessment that evaluates the following:
- filter type
- manufacturer and manufacturing method
- transportation method
- testing
- sterilization
- certification
- packaging, handling, and inspection procedures
- product type and product masking attributes
The goal of the risk assessment is to evaluate procedures in places as well as the likelihood of sterile filter damage and whether any such damage could be masked by product fouling, thereby supporting a justification to omit PUPSIT. Once complete, the assessment is submitted to regulators for review and comment. It is a highly involved, time-consuming process, and in many cases, it is more practical to implement PUPSIT.
However, there are unique instances where PUPSIT is not feasible, particularly with small volume batches in which a PUPSIT flush could consume too much (or all) of a product batch. If taking the risk assessment route, evaluate your product’s ability to mask and gather extremely thorough data to ensure compliance. Engage early with your QP to identify the strategy most likely to garner regulatory approval. As the subject matter experts of your product, your team must evaluate the regulations, how they apply, and whether PUPSIT is critical to your process.
For sponsors starting in the U.S. market but targeting eventual EU expansion, it is crucial to weigh the benefits of implementing PUPSIT from the outset of development versus waiting to adopt the process during regional expansion. Evaluate your manufacturing goals and intended batch size for commercialization to help define an effective multi-region strategy.
3. What Misconceptions Exist Surrounding PUPSIT?
Though PUPSIT is widely recognized as a vital implement, there is still, at times, a fundamental misunderstanding of PUPSIT and how it impacts manufacturing operations. These misconceptions can lead to concerns that PUPSIT increases the risk to a batch, delays batch release, or adds unnecessary costs. However, avoiding PUPSIT to minimize costs or delays can compromise product quality and potentially lead to non-compliance.
PUPSIT also has a misleading reputation for being overly complex. Though filter integrity testing is not inherently difficult, performing the test in situ introduces operational challenges. This is because in situ testing requires additional connection points, shutoff valves, and manual interventions on a sterile system, all of which can introduce potential failure points. It also requires operators to wet the filter prior to integrity testing. In practice, most PUPSIT failures observed have been the result of inadequate wetting, inconsistent techniques, or a lack of understanding of fluid dynamics concepts — issues that can be avoided with appropriate operator experience and training.
4. How Can You Guarantee PUPSIT Success?
PUPSIT is never one-size-fits-all; the approach is always specific to the product, filter, and assembly to which it is applied. For this reason, it is important to identify a PUPSIT approach that meets the unique needs of your product. With greater exposure to distinct scenarios, PUPSIT operators learn when and how to adjust, simplify, and apply specific techniques. For example, different sterilizing filters may require distinct filter wetting procedures. A sufficient volume of the wetting agent must be passed through the filter to fully wet the membrane and purge trapped air. In some cases, a filter may be difficult to wet, requiring adaptive techniques such as placing a pre-filter on the wetting agent to reduce the risk of airlock occurring and improving the success of wetting the sterilizing filters.
An experienced CDMO with a well-trained PUPSIT team offers a clear operational advantage, combining procedure expertise with institutional knowledge that enables them to anticipate challenges and respond effectively during testing. By partnering with a CDMO that routinely executes PUPSIT across diverse products and assemblies, you can ensure a PUPSIT strategy that is both precise and adaptable, while reducing operational risk and supporting consistent manufacturing outcomes.
When evaluating a potential partner’s PUPSIT capabilities, assembly modularity is an important consideration. Some CDMOs rely on a single, all-inclusive part number for each assembly; however, this approach is larger and more expensive, with each new client or process requiring an entirely new assembly. However, with a modular PUPSIT approach, assemblies are composed of multiple sub-assemblies, including different tubing sizes, flush bags, and filters, that can be mixed and matched based on process requirements. If one component is faulty, it can be replaced without changing the entire assembly. Thus, rather than maintaining a unique part number for each client, a CDMO that employs a modular PUPSIT approach can leverage a limited set of part numbers to support hundreds of clients, improving flexibility, reducing cost, and enabling faster, more reliable execution across diverse processes.
5. Why Should You Implement PUPSIT?
PUPSIT is an essential testing requirement for drug products intended for the EU market. Though misconceptions exist regarding the complexity and challenges of PUPSIT implementation, an experienced team can execute the process in a controlled, consistent, and reliable manner, enabling your team to secure the integrity of your sterile filters throughout manufacturing runs. Therefore, to protect product quality and support regulatory compliance, work with a CDMO that emphasizes modular assembly design, deep operator experience, and a disciplined technique for PUPSIT execution.