From Detection to Prediction: Modern Analytical Approaches for Nitrosamine Risk

Nitrosamines have been known carcinogens for decades, but their emergence in pharmaceutical products in 2018 transformed them into a central regulatory and analytical priority.¹ What began as a targeted investigation into a handful of small nitrosamines has since expanded into a complex, mechanism-driven discipline requiring predictive assessment, structural evaluation, and highly sensitive analytical methods.

Today, nitrosamine control is no longer about detecting a short list of known impurities. It is about understanding why nitrosamines form, where they may form across the product lifecycle, and how to anticipate and prevent their formation before they occur.

The Hidden Complexity of Nitrosamine Formation

Nitrosamine formation depends on 2 components: a nitrosating agent (typically nitrites) and an amine. Nitrites can come from many sources including nitrous acid, nitric oxides, and nitrates. When nitrites become acidified, they form nitrous acid, which can then react with an amine to generate a nitrosamine. They are metabolically activated in the liver which then allows them to cause DNA alkylation. This activation produces reactive intermediates capable of inducing base-pair mutations, particularly at the O₆-guanine position, during DNA replication.^1,2

There are 2 features that make nitrosamines uniquely challenging. First, when a nitrosamine is formed, it is stable and will not readily degrade into something else. Second, unlike elemental impurities or leachables, nitrosamine risk is not mitigated by oral administration. All routes of administration (oral, inhaled, injectable, topical products, etc) carry similar toxicological concern. This toxicological profile underpins the stringent acceptable intake (AI) limits, often in the low nanograms per day range, and the need for predictive, rather than reactive, control strategies.

Nitrites arise from numerous sources including in plant- or animal-derived excipients, as processing residuals, and are commonly present in water at low levels. Even a low level of nitrites may exceed a bit above the nitrosamine concern threshold. Typical nitrite levels from common excipients can average approximately 1 ppm—orders of magnitude higher than the nanogram-level thresholds relevant for nitrosamines.³ These excipients are commonly used in pharmaceutical products to optimize the safety and delivery of the active ingredient.

Secondary, tertiary, and quaternary amines are widespread in pharmaceuticals because they drive therapeutic activity. This ubiquity means many APIs inherently contain a “nitrosatable” site. Even if no nitrosamine is present in the API or excipient, the presence of an amine alone constitutes half of the formation pathway.

Conditions that drive formation. Nitrosation typically requires acidic conditions, which may arise during the following:

• granulation
• coating
• pH‑adjusted processing steps
• stability (eg, moisture‑driven hydrolysis).

The Expanding Universe of Nitrosamines

The first wave of regulatory action focused on a small set of nitrosamines: N-Nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), N-Nitrosomethylaminobutyric Acid (NMBA), and others, because they were detected in multiple products in 2018. These species were linked to common excipients, solvents, or synthetic routes. The landscape changed dramatically with the FDA’s 2023 guidance on nitrosamine drug substance–related impurities (NDSRIs). It became evident that there could be an infinite number of nitrosamines possible, because any secondary, tertiary, or quaternary amine has the risk of becoming a nitrosamine under the right conditions.

NDSRIs are formed when the API itself (or its impurities) undergoes nitrosation. This requires the following:

• structural assessment
• potency categorization
• toxicological read‑across
• compound‑specific AI limits.

The FDA’s structure-based potency scoring system allows companies to derive acceptable intake limits even when no carcinogenicity data exist for the specific NDSRI. The guidance also allows sponsors to use compound-specific data or read-across assessment from a scientifically justified surrogate to better understand the toxicological risk of a specific NDSRI.⁴

Building a Modern Nitrosamine Risk Assessment

A robust nitrosamine risk assessment must evaluate the entire product lifecycle, from raw materials to long‑term stability. For raw materials, key considerations should include the origin of materials (plant- or animal-derived excipients often contain nitrates and nitrites), the synthetic route (solvents, catalysts, intermediates, side reactions), process impurities and degradants that may introduce amines or nitrites, and the carryover risk from reagents or processing aids. Additionally, even when vendors state that a material has “no nitrosamine risk”, they may still contain one half of the formation equation, either an amine or a nitrosating agent. The potential for the combination of nitrosamine precursors in the drug product needs to be considered.

Drug product manufacturing and packaging. Excipients such as microcrystalline cellulose, lactose, mannitol, povidone, and talc frequently contain trace nitrites. When combined with an API containing a precursor amine, the risk becomes product‑specific.

Manufacturing steps to evaluate risk include the following:

• pH adjustments
• thermal processing
• granulation solvents
• moisture exposure
• packaging interactions.

Nitrosamine formation can occur during storage due to the following:

• nitrate → nitrite reduction
• degradation of the API to form new amines
• migration of nitrosating species from packaging.

It is crucial to understand the presence of nitrites in the formulation and question whether there is a potential to form a nitrosamine while the product is on the shelf.

Analytical Strategies: From Screening to Confirmatory Testing

The United States Pharmacopeia chapter <1469> Nitrosamine Impurities and various regulatory methods provide validated liquid chromatography tandem mass spectrometry (LC-MS)/MS and gas chromatography (GC)MS approaches for the initial 7 nitrosamines.⁵ These methods remain essential for products with known risks. However, NDSRIs are more challenging. This is because they often lack reference standards, have poor ionization efficiency, require ultra‑low detection limits, and demand compound‑specific method development.

Common Pitfalls and Regulatory Lessons Learned

Across industry, several recurring issues have emerged. First, there has been an over-reliance on vendor statements. As stated earlier, vendor declarations of ‘no nitrosamine risk’ often refer only to the absence of nitrosamines in the material and do not necessarily refer to the absence of nitrites or amines. Although there may be 5 or more materials that have ‘no risk’, there may be nitrite present in an excipient, and a secondary amine within the API. Furthermore, even if there is no nitrosamine present at release, formation during storage remains a regulatory concern.⁴

An additional recurring issue is the misclassification of nitrogen-containing functional groups. Not all nitrogen-containing groups are nitrosatable. The FDA guidance clarifies that nitro, amide, and urea groups do not form nitrosamines.⁴

Moreover, even ppm-level nitrites can generate nitrosamine levels above the nitrosamine AI limits, so it is critical that teams avoid assuming low nitrite levels are “safe”.

Toward Predictive Control: A Forward‑Looking Framework

The industry is moving from detection to prediction and anticipating nitrosamine formation before it occurs. A modern framework begins with a mechanistic understanding, mapping potential nitrosation pathways, including API degradation, excipient interactions, packaging contributions, and pH‑driven transformations. The next step would be a structural assessment, using the FDA’s potency scoring to classify NDSRIs and derive AI limits, before moving to a lifecycle-wide risk assessment to evaluate raw materials, manufacturing, packaging, and stability as an integrated system. It is advisable to then include analytical innovation to develop high-sensitivity LC MS/MS methods, derivatization strategies, nitrite‑specific assays, and stability‑indicating methods. The final part of the framework should include continuous regulatory alignment, to understand the evolving expectations for justification, testing, and control strategies.

Nitrosamine Control Evolution

Nitrosamine control has rapidly evolved from a narrow analytical challenge into a multidisciplinary, predictive science. The combination of ubiquitous nitrite sources, therapeutically valuable amine‑containing APIs, and low toxicological thresholds means that nitrosamine formation must be anticipated, not merely detected.

It is crucial for companies to evaluate the full product lifecycle to understand nitrosamine risk and if testing is required. By integrating mechanistic understanding, structural assessment, sensitive analytics, and lifecycle‑wide risk evaluation, the industry can move confidently toward proactive, predictive nitrosamine control.

References

1. M7(R2): Assessment and Control of DNA Reactive (Mutagenic) Impurities in Pharmaceuticals to Limit Potential Carcinogenic Risk. International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH). Final version adopted April 3, 2023.

2. Fahrer J, Christmann M. DNA alkylation damage by nitrosamines and relevant DNA repair pathways. International Journal of Molecular Sciences. 2023;24(5):4684. doi:10.3390/ijms24054684.

3. Boetzel R, Schlingemann J, Hickert S, et al. A nitrite excipient database: A useful tool to support N-Nitrosamine risk assessments for drug products. Journal of Pharmaceutical Sciences. 2023;112(6):1615-1624. doi:10.1016/j.xphs.2022.02.022.

4. Recommended Acceptable Intake Limits for Nitrosamine Drug Substance-Related Impurities (NDSRIs): Guidance for Industry. U.S. Food and Drug Administration. August 2023.

5. General Chapter <1469> Nitrosamine Impurities. USP-NF. United States Pharmacopeia. Official as of December 1, 2021.

About the Author

Chris Williams serves as executive director, Analytical Development ILM at Alcami, bringing more than a decade of experience in analytical development, quality control, and laboratory operations.

He earned a Bachelor of Science in Chemistry in 2010 and a Master of Science in Chemistry in 2011 from East Carolina University. Chris joined AAI, now Alcami, in 2011 as a Development/QC Scientist. In 2013, he began supervising a laboratory team focused on high-throughput manufacturing release. In 2014, he moved into the management of development services and has since progressed to oversee elemental impurities, biologics, extractables and leachables, nitrosamines, specialty testing, raw material release, microbiology, and all Wilmington laboratory operations.