Overview: Why In-Use Stability Matters More Than Ever
AAPS Science360. Presenters F. 02/11/26; 4194066
Topic: Regulatory
Kim Huynh-Ba
Sherilyn Campie
Vinaya Kapoor
Lori McCaig
Dan Willingmyre
Kayla Woodlief, B.S.
Abstract/Article
References
In-use stability studies are designed to answer a deceptively simple question: Does a drug product remain safe, effective, and fit for use after it leaves its original container and is prepared for administration? In practice, answering that question is anything but simple. Once a product is diluted, transferred into infusion bags or syringes, exposed to light and temperature excursions, or held prior to administration, its quality attributes can change in ways not captured by traditional stability programs.
Despite their direct relevance to patient safety, in-use stability studies remain one of the least harmonized areas of pharmaceutical development. Regulatory agencies universally expect these data to support labeling and administration instructions yet provide limited prescriptive guidance on how studies should be designed or evaluated. The result is variability—across companies, programs, and regions—in both expectations and execution.
This review, led by the AAPS Stability Community, synthesizes industry experience, regulatory feedback, and cross-company dialogue to outline a practical, risk-based framework for in-use stability studies. Rather than proposing new requirements, the paper focuses on aligning scientific rigor with real-world use and regulatory intent. The full paper can be accessed at Review of in-use stability: current practices, emerging requirements, expectations, challenges and trends. And here are some highlights.
In-Use Stability: Bridging the Gap Between the Label and the Patient
One of the central messages of the paper is the mismatch between regulatory expectations and available guidance. Health authorities globally expect in-use stability data to support labeling claims, pharmacy manuals, and administration instructions. However, most foundational guidance documents, including ICH Q1A(R2)—provide only high-level principles and little operational detail on how in-use studies should be designed, executed, or evaluated.
As a result, sponsors often rely on product-specific feedback received during regulatory interactions. While this input can be valuable, it frequently varies between regions and even between reviewers, leading to divergent expectations for the same product. This lack of harmonization drives inefficiencies such as repeated studies, country-specific labeling, and conservative design choices that increase cost without necessarily improving patient safety.
The paper highlights ongoing efforts to address this gap, including the revision of ICH Q1A(R2), which is expected to include more explicit considerations for in-use stability. Until such guidance is finalized, the authors emphasize the importance of early and proactive engagement with regulators, especially for complex products or non-standard administration practices.
Designing Studies That Reflect How Products Are Actually Used
A central theme of the paper is that in-use stability studies must reflect real clinical practice, not idealized laboratory conditions. Products may be prepared in hospital pharmacies, transported to infusion suites, held to reduce patient wait times, or administered using a wide range of bags, tubing, filters, and pumps. Each step introduces potential stressors that can affect product quality.
Effective study design therefore starts with understanding clinical workflows. Dose range, diluent type, infusion duration, and container materials should all be selected to bracket realistic worst-case scenarios. Testing only a narrow, “typical” condition may be efficient, but it often fails to support the full range of clinical use.
Cross-functional input is essential. Clinical teams clarify how products are administered in practice, while quality, regulatory, and supply chain groups help anticipate global variability in equipment and procedures. Incorporating these perspectives early reduces the risk of late-stage redesigns or post-approval commitments.
Analytical Strategy: Focus on What Matters Most
Analytical strategy is another central theme. Analytical testing for in-use stability should begin with the drug product release and stability panel—but it should not end there. Dilution and handling can alter sample behavior, rendering some standard assays unsuitable or insufficiently sensitive. Applying release methods without confirming their suitability for in-use samples can generate misleading data or false failures.
The paper strongly supports a risk-based, phase-appropriate analytical strategy. In early development, method qualification or suitability assessments may be sufficient, provided they demonstrate reliable detection of critical quality attributes. As programs advance, expectations increase, and full validation or enhanced verification becomes necessary.
Similarly, while stability specifications are commonly used to evaluate in-use data, they may not always be appropriate for diluted samples. Parameters such as pH or protein concentration may shift due to dilution alone, without indicating degradation or loss of efficacy. In such cases, scientifically justified acceptance criteria—grounded in patient risk—are often more meaningful than rigid application of standard limits. Overall, the authors advocate focused testing of critical quality attributes, informed by risk assessment, rather than broad, unfocused test panels that add complexity without commensurate value
Lifecycle Perspective and Microbial Risk
The paper clearly positions in-use stability as a lifecycle activity rather than a one-time requirement. Early-phase studies support safe administration in clinical trials, often leveraging platform knowledge or simplified designs. As development progresses, studies become more comprehensive to support registration, labeling, and global commercialization.
Guidelines generally recommend using two lots: one recently manufactured and one approaching end of shelf-life. This approach helps ensure that in-use performance is acceptable across the product’s lifecycle. In some cases, studies on aged material may be deferred as post-approval commitments, but this should be strategically justified.
Microbial hold studies receive particular attention. The need for microbial testing depends on factors such as hold-time, temperature, formulation, and whether the product is single-dose or multi-dose. For commercial applications, microbial hold studies are typically required for hold times exceeding four hours. For clinical applications, expectations vary but remain risk based. The authors emphasize that microbial safety is inseparable from chemical and physical stability when defining in-use conditions.
For complex dosage forms or multiple administration configurations, the paper supports the use of design of experiments, bracketing, and worst-case selection to reduce testing burden while maintaining scientific rigor.
Conclusion: Toward a Consistent, Risk-Based Framework
In-use stability studies are no longer a peripheral consideration—they are a critical component of ensuring that drug products remain safe and effective from preparation to patient administration. This paper reframes in-use stability as a patient-focused scientific discipline—one that benefits from consistency, proportionality, and real-world relevance.
By adopting a structured, risk-based framework and aligning study design with clinical practice and regulatory intent, sponsors can improve study efficiency, reduce redundancy, and support clearer, more consistent labeling. As regulatory guidance evolves, particularly through updates to ICH Q1A(R2), the principles outlined in this paper provide a practical foundation for harmonizing expectations and strengthening patient-centric product quality across the pharmaceutical lifecycle.
In-use stability studies are designed to answer a deceptively simple question: Does a drug product remain safe, effective, and fit for use after it leaves its original container and is prepared for administration? In practice, answering that question is anything but simple. Once a product is diluted, transferred into infusion bags or syringes, exposed to light and temperature excursions, or held prior to administration, its quality attributes can change in ways not captured by traditional stability programs.
Despite their direct relevance to patient safety, in-use stability studies remain one of the least harmonized areas of pharmaceutical development. Regulatory agencies universally expect these data to support labeling and administration instructions yet provide limited prescriptive guidance on how studies should be designed or evaluated. The result is variability—across companies, programs, and regions—in both expectations and execution.
This review, led by the AAPS Stability Community, synthesizes industry experience, regulatory feedback, and cross-company dialogue to outline a practical, risk-based framework for in-use stability studies. Rather than proposing new requirements, the paper focuses on aligning scientific rigor with real-world use and regulatory intent. The full paper can be accessed at Review of in-use stability: current practices, emerging requirements, expectations, challenges and trends. And here are some highlights.
In-Use Stability: Bridging the Gap Between the Label and the Patient
One of the central messages of the paper is the mismatch between regulatory expectations and available guidance. Health authorities globally expect in-use stability data to support labeling claims, pharmacy manuals, and administration instructions. However, most foundational guidance documents, including ICH Q1A(R2)—provide only high-level principles and little operational detail on how in-use studies should be designed, executed, or evaluated.
As a result, sponsors often rely on product-specific feedback received during regulatory interactions. While this input can be valuable, it frequently varies between regions and even between reviewers, leading to divergent expectations for the same product. This lack of harmonization drives inefficiencies such as repeated studies, country-specific labeling, and conservative design choices that increase cost without necessarily improving patient safety.
The paper highlights ongoing efforts to address this gap, including the revision of ICH Q1A(R2), which is expected to include more explicit considerations for in-use stability. Until such guidance is finalized, the authors emphasize the importance of early and proactive engagement with regulators, especially for complex products or non-standard administration practices.
Designing Studies That Reflect How Products Are Actually Used
A central theme of the paper is that in-use stability studies must reflect real clinical practice, not idealized laboratory conditions. Products may be prepared in hospital pharmacies, transported to infusion suites, held to reduce patient wait times, or administered using a wide range of bags, tubing, filters, and pumps. Each step introduces potential stressors that can affect product quality.
Effective study design therefore starts with understanding clinical workflows. Dose range, diluent type, infusion duration, and container materials should all be selected to bracket realistic worst-case scenarios. Testing only a narrow, “typical” condition may be efficient, but it often fails to support the full range of clinical use.
Cross-functional input is essential. Clinical teams clarify how products are administered in practice, while quality, regulatory, and supply chain groups help anticipate global variability in equipment and procedures. Incorporating these perspectives early reduces the risk of late-stage redesigns or post-approval commitments.
Analytical Strategy: Focus on What Matters Most
Analytical strategy is another central theme. Analytical testing for in-use stability should begin with the drug product release and stability panel—but it should not end there. Dilution and handling can alter sample behavior, rendering some standard assays unsuitable or insufficiently sensitive. Applying release methods without confirming their suitability for in-use samples can generate misleading data or false failures.
The paper strongly supports a risk-based, phase-appropriate analytical strategy. In early development, method qualification or suitability assessments may be sufficient, provided they demonstrate reliable detection of critical quality attributes. As programs advance, expectations increase, and full validation or enhanced verification becomes necessary.
Similarly, while stability specifications are commonly used to evaluate in-use data, they may not always be appropriate for diluted samples. Parameters such as pH or protein concentration may shift due to dilution alone, without indicating degradation or loss of efficacy. In such cases, scientifically justified acceptance criteria—grounded in patient risk—are often more meaningful than rigid application of standard limits. Overall, the authors advocate focused testing of critical quality attributes, informed by risk assessment, rather than broad, unfocused test panels that add complexity without commensurate value
Lifecycle Perspective and Microbial Risk
The paper clearly positions in-use stability as a lifecycle activity rather than a one-time requirement. Early-phase studies support safe administration in clinical trials, often leveraging platform knowledge or simplified designs. As development progresses, studies become more comprehensive to support registration, labeling, and global commercialization.
Guidelines generally recommend using two lots: one recently manufactured and one approaching end of shelf-life. This approach helps ensure that in-use performance is acceptable across the product’s lifecycle. In some cases, studies on aged material may be deferred as post-approval commitments, but this should be strategically justified.
Microbial hold studies receive particular attention. The need for microbial testing depends on factors such as hold-time, temperature, formulation, and whether the product is single-dose or multi-dose. For commercial applications, microbial hold studies are typically required for hold times exceeding four hours. For clinical applications, expectations vary but remain risk based. The authors emphasize that microbial safety is inseparable from chemical and physical stability when defining in-use conditions.
For complex dosage forms or multiple administration configurations, the paper supports the use of design of experiments, bracketing, and worst-case selection to reduce testing burden while maintaining scientific rigor.
Conclusion: Toward a Consistent, Risk-Based Framework
In-use stability studies are no longer a peripheral consideration—they are a critical component of ensuring that drug products remain safe and effective from preparation to patient administration. This paper reframes in-use stability as a patient-focused scientific discipline—one that benefits from consistency, proportionality, and real-world relevance.
By adopting a structured, risk-based framework and aligning study design with clinical practice and regulatory intent, sponsors can improve study efficiency, reduce redundancy, and support clearer, more consistent labeling. As regulatory guidance evolves, particularly through updates to ICH Q1A(R2), the principles outlined in this paper provide a practical foundation for harmonizing expectations and strengthening patient-centric product quality across the pharmaceutical lifecycle.
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ICH Q1A(R2) – Stability Testing of New Drug Substances and Products.
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EMA CPMP/QWP/2934/99 – Note for Guidance on In-Use Stability Testing of Human Medicinal Products.
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FDA (2018) – Mixing, Diluting, or Repackaging Biological Products Outside the Scope of an Approved BLA.
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Blümel et al., 2023 – Current Industry Best Practice on In-Use Stability and Compatibility Studies for Biological Products, Journal of Pharmaceutical Sciences.
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D. Willingmyre, et al., Review of In-Use Stability: Current Practices, Emerging Requirements, Expectations, Challenges and Trends, AAPS Open, February 2026. Accessed on 02/09/2026 at Review of in-use stability: current practices, emerging requirements, expectations, challenges and trends | AAPS Open | Springer Nature Link
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