Managing Extractables And Leachables In HPAPI Manufacturing

By Williams Olughu, Ph.D., Ipsen

The risk brought by extractables and leachables (E&L) is tightly controlled in any drug product, but it’s especially important to monitor and mitigate in highly potent active pharmaceutical ingredients (HPAPIs).

In drug product manufacturing, controlling sources of contamination is crucial to ensure patient safety.¹ E&L are a subset of contaminants that require mitigation. Extractables represent compounds released from materials under extreme conditions (such as high temperature and pressure), which are typically simulated in the laboratory.²

Conversely, leachables are the chemical entities that are released from materials into the drug product under normal manufacturing, storage, and use conditions.

Thus, leachables are classified as a form of extractables, meaning extractables studies are essential for predicting what might leach.

The presence of any impurity, including leachables, can compromise the quality, stability, or safety of a drug product.^2,3 Therefore, all regulatory bodies mandate E&L assessment to prevent harmful chemicals from reaching patients.¹ The risk of E&L in the manufacture of HPAPIs is pronounced due to the inherent characteristics of low therapeutic dose, high potency, and toxicity.⁴ Consequently, HPAPIs require a more stringent approach to E&L control to protect patient safety and maintain product quality throughout their life cycle.

These defining features of HPAPIs fundamentally amplify the risks associated with E&L, especially regarding patient safety. For patients receiving a highly potent compound with a narrow therapeutic window and potential adverse effects, the introduction of additional toxic substances through leachables, even at levels deemed negligible for conventional drugs, can alter this risk-benefit balance.⁵ The two main risks are as follows.  

1. The interaction of leachables with the HPAPI may potentially cause degradation or the formation of new chemical entities. For HPAPIs, where precise dosing is paramount for efficacy and safety, degradation can lead to reduced potency, rendering a vital therapy ineffective.⁶ Alternatively, such interactions could create a modified API or an API-leachable adduct with altered potency or an entirely different, potentially more harmful, toxicity profile.
2. The low therapeutic dose of many HPAPIs introduces an additional layer of risk; the relative concentration of a leachable compared to the API can be significantly higher than in conventional drugs. For example, a microgram of leachable in a 1 mg HPAPI dose is 1,000 ppm relative to the API, whereas the same amount in a 500 mg dose is only 2 ppm. This elevated relative concentration increases the potential for the leachable to exert direct toxicological effects or to interact significantly with the API.

Why Do Lower Doses Mean Lower Patient Exposure Thresholds?

Consequently, these heightened risks directly dictate stricter safety thresholds for leachables in HPAPI manufacture, particularly impacting the analytical evaluation threshold (AET) and permitted daily exposure (PDE). The AET defines the level at which an extractable or leachable substance requires identification, quantification, and toxicological assessment.⁷ While a general safety concern threshold (SCT) of 1.5 µg/day is typical for organic leachables in injectables, this level may be excessively high for certain HPAPI scenarios, especially if the leachable's toxicology is comparable to the HPAPI or if multiple leachables are present.⁷

The PDE denotes a substance-specific daily exposure that is unlikely to cause adverse effects over a lifetime.⁸ For HPAPIs, the API's own PDE is inherently very low. Any leachables in an HPAPI product must have an acceptable daily intake that represents an exceedingly small fraction of its own PDE (if known) or, more likely, a fraction of the HPAPI's already low PDE. This critical constraint inevitably necessitates exceptionally low AETs for leachables in HPAPI products. The relationship between AET, PDE, and daily dose indicates that even low concentrations (ppm) of a leachable in a low-dose HPAPI can lead to a patient's daily intake approaching or exceeding its very low safety threshold.⁸

Meeting these ultra-low thresholds presents significant analytical challenges. The primary hurdle involves achieving ultra-low detection and quantification limits, often required in the parts per billion (ppb) or even sub-ppb range, pushing analytical instrumentation to its performance limits. HPAPI formulations can also present intricate matrices, such as sophisticated delivery systems (like lipid nanoparticles) or biologics (like antibody-drug conjugates (ADCs)), which interfere considerably with analytical methods, complicating accurate quantification.^9,10

Identifying unknown leachables at trace concentrations is challenging and requires the use of multiple orthogonal techniques, such as GC-MS, LC-MS, and ICP-MS.¹¹ The reliance on surrogate standards for quantifying unknowns introduces uncertainty, which is less acceptable when safety margins are critically narrow.¹⁰ Potential reactivity between HPAPIs and leachables, resulting in the formation of new adducts, along with concerns about leachable stability within the formulation, further complicates the analytical assessment. Navigating these factors successfully requires cutting-edge instrumentation, rigorous method development, highly skilled personnel, and a robust quality system.

Which Materials Present The Greatest Extractable, Leachable Risks?

The key materials and components that pose significant E&L concerns in HPAPI manufacturing, owing to their direct contact with the product and the increased risk of being sources of impurities, are discussed below.

Primary packaging components are critical as they maintain direct, long-term contact with the final product.

• Elastomeric closures (stoppers, plungers, seals) are notorious for leaching complex mixtures of oligomers, curing agents, antioxidants, and nitrosamines. Outgassing from stoppers is a particular concern for lyophilized HPAPIs, where volatile leachables can adsorb onto the high-surface-area cake over time. FDA deficiency letters frequently highlight inadequate E&L data for stoppers.¹²
• Plastic containers (such as bottles, vials, bags, and syringes) can leach monomers, oligomers, and additives into the surrounding environment. The migration of substances from labels, inks, and adhesives through semi-permeable plastic also poses a risk.¹²
• Glass containers (vials, syringes), while relatively inert, can leach alkali ions or metal oxides. This is particularly true of non-Type I glass. Coatings, such as silicone oil, are also potential sources of leachables.
• Labels, inks, and adhesives, though sometimes secondary, pose risks via migration, especially with plastic containers.

Single-use technologies (SUTs) are increasingly used in manufacturing and are a major source of E&L.

While offering advantages such as reduced cross-contamination risk (vital for HPAPIs), their polymeric nature means that components (such as filters, tubing, etc.) can leach antioxidants, slip agents, monomers, and oligomers.^13,14 The risk is highest from SUTs used close to the final product, as there are fewer subsequent purification steps, and HPAPI's low AETs make trace levels significant. Some of the most common SUTs and their E&L risks include:

• Filters, typically composed of membranes (such as polyethersulfone, polyvinylidene difluoride, or cellulose esters) and housings (made of polypropylene or other plastics), can leach manufacturing residues, wetting agents, and material degradation products from both the membranes and housings. Leachables from filters used in final sterile filtration steps are a significant concern for HPAPIs due to the low acceptable impurity levels. Filter material compatibility and the potential adsorption of HPAPIs also require careful evaluation to prevent yield loss during the manufacture of these high-value products.¹⁰ 
• Chromatography resins, used for purification (crucial for biologic HPAPIs like ADCs), can leach ligands (e.g., Protein A), backbone components, or processing chemicals. Leached Protein A is a known immunogen.¹⁵ For ADCs, leachables may interact with the antibody, linker, or cytotoxic payload, affecting purity, stability, or payload release. Additionally, in cases where resin reuse is implemented to reduce manufacturing costs, it increases the complexity of managing the E&L profile throughout the resin's lifespan.¹⁶
• Tubing, which is widely used for fluid transfer and made from materials such as silicone or thermoplastic elastomers, can leach monomers, catalysts, plasticizers, and degradation products.¹² The cumulative leaching from extensive tubing networks throughout the manufacturing process can become significant, considering the low AETs applicable to HPAPIs.

Raw materials, including excipients used in formulation, can also be sources of E&Ls.

Excipients may contain impurities that can interact with packaging or equipment, leading to the formation of leachables.^7,11 United States Pharmacopeia (USP) indicates that E&Ls can chemically react with both APIs and excipients. Furthermore, the carryover of substances from previous manufacturing steps of the API itself can also act as a source of contamination in the final product.  

Effectively managing these risks requires a comprehensive and proactive approach to mitigation, which should include:

1. Proactive material selection and qualification: This begins by leveraging all available vendor data but requires thorough in-house extractables studies, particularly for critical components, tailored to HPAPI-specific conditions. Initiating these studies early is essential.^11,17
2. Equipment design and engineering controls: Although containments are primarily designed (e.g., isolators, closed systems) to protect personnel from HPAPIs, these systems can also offer secondary benefits by safeguarding the product from external E&L sources. This secondary consideration should be included as an up-front design specification.
3. Process optimization: Minimizing contact time, temperature, and the use of aggressive solvents where feasible can reduce leaching. The significant challenge lies in cleaning validation in shared facilities. Where aggressive cleaning agents are needed for potent residues, they must be thoroughly rinsed to prevent them from becoming leachables. Therefore, their long-term impact on equipment integrity must be actively monitored, as degradation increases E&L.¹³
4. Selection of appropriate primary packaging: Choosing materials that demonstrate low E&L profiles, show proven chemical compatibility with the HPAPI formulation, and are suitable for maintaining stability is paramount. Special attention is required for lyophilized products and low-outgassing stoppers.¹¹
5. Robust E&L testing programs: This involves developing and validating highly sensitive, product-specific analytical methods using orthogonal techniques (LC-MS, GC-MS, ICP-MS). Integrating leachable testing into stability studies is crucial for tracking leaching and any potential long-term impact. Setting scientifically justified AETs and conducting thorough toxicological assessments of identified leachables are critical steps in ensuring safety.^9,11

Ultimately, the regulatory landscape has a significant influence on E&L management for HPAPIs. Key guidance is provided by USP General Chapters <661> series, <1663>, <1664>, <665>, <1665>, and <381>, which outline requirements for packaging and manufacturing components. FDA regulations (21 CFR 211.65(a)) and guidance on container closure systems emphasize the necessity for non-reactive, non-additive, non-absorptive materials.

The EMA guideline on health-based exposure limits, while focused on cross-contamination, offers principles for PDE derivation that are highly pertinent to establishing stringent safety thresholds for leachables in HPAPIs. International harmonization through ICH Q3E (in development) aims to standardize E&L assessment globally. In addition, ICH guidelines, such as M7 (mutagenic impurities) and Q3D (elemental impurities), are also relevant if these types of leachables are identified.

For HPAPIs, E&Ls are high-risk, necessitating extensive data, rigorous testing, and robust scientific justification to ensure product safety.^7,9 Hence, the standard for justifying the omission of studies or the acceptance of higher leachable levels is exceptionally high.

Conclusion

The high potency and toxicity profile of HPAPIs fundamentally elevates the challenge of E&L management from a routine quality control exercise to a critical safety imperative. This requires ultra-low safety thresholds, advanced analytical capabilities, meticulous material selection and qualification, and stringent process controls throughout the entire product life cycle.

A comprehensive, risk-based approach, aligned with evolving global regulatory expectations and underpinned by a deep understanding of both material science and toxicology, is indispensable for successfully developing and manufacturing safe and effective HPAPI drug products.

As the pharmaceutical landscape evolves with more complex, potent molecules, analytical advancements and predictive tools will become increasingly vital in navigating these intricate E&L challenges.

References:

1. G. L. Erexson, K. L. Li, C. M. Stults, T. Broschard, and R. Brown, “Evaluation of Leachable Substances from Materials with Applications in Foods and Pharmaceuticals: Science-and Risk-Based Approaches,” Mar. 2018. Accessed: Jul. 01, 2025. [Online]. Available: https://www.toxicology.org/education/ce/docs/SOT_2018_PM10.pdf
2. “Extractables vs. Leachables | Ensuring Drug Safety and Compliance - UPM Pharmaceuticals.” Accessed: Jul. 01, 2025. [Online]. Available: https://www.upm-inc.com/extractables-vs-leachables
3. G. Murillo and P. Pekos, “Top 7 Considerations When Conducting Extractable And Leachable Studies”, Accessed: Jul. 01, 2025. [Online]. Available: https://www.dalton.com/Content/files/7-considerations-conducting-extractables-leachables-studies.pdf
4. “Highly Potent API (HPAPI) | API Manufacturing Service | CMOs.” Accessed: Jul. 01, 2025. [Online]. Available: https://www.pharmacompass.com/pharma-blog/overview-of-highly-potent-apis-leading-cmos-cdmos-offering-hpapi-development-commercial-manufacture-among-other-highly-potent-api-services
5. “The rules on HPAPI containment in high potent manufacturing.” Accessed: Jul. 02, 2025. [Online]. Available: https://www.pharmaceutical-technology.com/sponsored/understanding-the-rules-on-hpapi-containment-in-high-potent-manufacturing/
6. “What Are Extractables and Leachables? | Pharma Risk Assessments.” Accessed: Jul. 02, 2025. [Online]. Available: https://www.qbdgroup.com/en/blog/extractables-leachables-pharmaceutical-risk-assessment
7. S. Antonio, T. Scott, and C. Kyle, “Exploring extractable and leachable testing strategies for parenterals,” 2024. Accessed: Jul. 02, 2025. [Online]. Available: https://aptar.com/resources/exploring-extractable-and-leachable-testing-strategies-for-parenterals/
8. “Guideline on setting health based exposure limits for use in risk identification in the manufacture of different medicinal products in shared facilities,” Nov. 2014. Accessed: Jul. 02, 2025. [Online]. Available: https://www.ema.europa.eu/en/documents/scientific-guideline/guideline-setting-health-based-exposure-limits-use-risk-identification-manufacture-different-medicinal-products-shared-facilities_en.pdf
9. “EXTRACTABLES & LEACHABLES - Detecting the Unknown With Extractables & Leachables Analysis.” Accessed: Jul. 02, 2025. [Online]. Available: https://drug-dev.com/extractables-leachables-detecting-the-unknown-with-extractables-leachables-analysis/
10. “Highly Potent APIs (HPAPIs) in Pharmaceutical Manufacturing: Challenges, Strategies and Future Outlook - PharmaSource.” Accessed: Jul. 02, 2025. [Online]. Available: https://pharmasource.global/content/guides/category-guide/highly-potent-apis-hpapis-in-pharmaceutical-manufacturing-challenges-strategies-and-future-outlook/
11. “Extractables and Leachables: Best Practices & Key Considerations.” Accessed: Jul. 02, 2025. [Online]. Available: https://adragos-pharma.com/extractables-and-leachables-best-practices-and-key-considerations/
12. Redd, “Extractable and Leachable Challenges; from a generic injectable drug development perspective,” 2017. Accessed: Jul. 02, 2025. [Online]. Available: https://accessiblemeds.org/wp-content/uploads/2024/09/Andrea-Redd.pdf
13. Steve Williams, “Controlling Cross Contamination in a Biologics Facility,” Accessed: Jul. 06, 2025. [Online]. Available: https://dcvmn.org/wp-content/uploads/2015/07/cbe_-025_x_contam_v2_dcvmn_.pdf
14. “Extractables and Leachables Risk Assessment for Single-Use Systems.” Accessed: Jul. 06, 2025. [Online]. Available: https://www.sigmaaldrich.com/GB/en/technical-documents/technical-article/pharmaceutical-and-biopharmaceutical-manufacturing/extractables-leachables-risk-assessment-single-use-systems
15. N. Ravi, J. Huerta, and G. Ferreira, “Evaluating multiproduct chromatography Protein A resin reuse for monoclonal antibodies in biopharmaceutical manufacturing,” Biotechnol Prog, vol. 39, no. 3, May 2023, doi: 10.1002/BTPR.3333.
16. L. Wang et al., “A safe, effective, and facility compatible cleaning in place procedure for affinity resin in large-scale monoclonal antibody purification,” J Chromatogr A, vol. 1308, pp. 86–95, Sep. 2013, doi: 10.1016/j.chroma.2013.07.096.
17. E. Jao, “Extractable/Leachable assessment of manufacturing equipment components-OPQ’ s perspective,” 2024. Accessed: Jul. 06, 2025. [Online]. Available: https://accessiblemeds.org/wp-content/uploads/2024/12/GRxBiosims-2024-PPT-Edwin-Jao.pdf
18. “Understanding the Challenges and Opportunities of HPAPI Manufacturing.” Accessed: Jul. 06, 2025. [Online]. Available: https://powdersystems.com/2023/11/understanding-challenges-opportunities-hpapi-manufacturing/
19. “Enhancing Safety and Efficiency in HPAPI Manufacturing: Best Practices and Trends.” Accessed: Jul. 06, 2025. [Online]. Available: https://www.seqens.com/knowledge-center/enhancing-safety-and-efficiency-in-hpapi-manufacturing-best-practices-and-trends/

About The Author:

Williams Olughu, Ph.D., is a senior principal scientist at Ipsen Biopharmaceuticals Ltd. in the United Kingdom, where he serves as the CMC technical lead for one of the company’s antibody-drug conjugate programs. He is a Royal Academy of Engineering visiting professor at Loughborough University and an editorial board member for the World Journal of Microbiology and Biotechnology and the Journal of Chemical Technology and Biotechnology.