An introduction to nitrosamines
In 2018, the discovery of nitrosamine impurities in widely prescribed medicines triggered recalls across global markets and swiftly reshaped regulatory expectations. What initially appeared to be an isolated contamination event exposed a broader vulnerability in pharmaceutical drug development. Nitrosamines were identified across multiple products and therapeutic classes linked to synthesis conditions, raw materials, and storage environments. The issue was not confined to a single manufacturer or region, and exposed gaps in how impurity risk was anticipated and controlled. Between 2018 and 2020, nitrosamine risk assessment moved from a technical afterthought to a regulatory priority.
Testing can confirm the presence of a nitrosamine impurity, but it cannot remove the conditions that allow it to form. That distinction reshaped regulatory expectations. Today, agencies such as the U.S. Food and Drug Administration (FDA) and European Medicines Agency (EMA) expect integrated life cycle risk management rather than reactive testing alone. Nitrosamine control now intersects with route selection, excipient strategy, packaging decision, and long-term stability planning. Late identification of nitrosamine risk can disrupt development timelines and introduce regulatory uncertainty. Early integration reduces cost, protects supply, and strengthens competitive position.
Where nitrosamine risk begins
Nitrosamine risk begins in development. For Bridget Sykes, Senior Scientist at Douglas CDMO, the starting point is clear:
“The nitrosamine risk should be considered quite early in the drug development life cycle. You want to get it started as early as possible so that risks and mitigation strategies can be identified and implemented as early as practical.”
While the final, comprehensive risk assessment that supports product safety may not be required until commercial scale up, that does not make early development a low-risk territory.
“You don’t need the final risk assessment to be complete until commercial scale up, but you absolutely want to start early. Some mitigation strategies involve fundamental changes to a synthesis or to a drug product. Identifying a nitrosamine risk early gives you the flexibility to make meaningful changes,” says Bridget.
The critical question is no longer whether a nitrosamine can be detected; it is whether the chemistry and conditions could allow one to form.
Early design signals
Early nitrosamine risk assessments are driven by mechanism-based evaluations rather than by initial analytical testing. As Bridget explains, the first indicators are often embedded in process chemistry.
“The presence of secondary amines in materials is an immediate red flag. Even tertiary amine solvents can carry low levels of secondary amines as impurities, and under favorable conditions, those impurities can act as precursors to nitrosamine formation.”
Formation also requires a nitrosating agent. When deliberately introduced during synthesis, these are straightforward to identify. More often, the concern lies in trace contamination. “Residual nitrite in excipients is a well-recognized example,” Bridget notes.
The interplay between amines, nitrosating agents, and reaction conditions explains why dosage form does not insulate a product from risk. Regulators distinguish between nitrosamine drug substance–related impurities (NDSRIs) and small-molecule nitrosamines arising from solvents, reagents or excipients. Risk assessment, therefore, extends beyond the active pharmaceutical ingredient (API) and into formulation design.
“Nitrosamine control is not confined to a single unit operation or discipline. It’s a systems consideration.”
BRIDGET SYKES, NEW PRODUCT DEVELOPMENT SENIOR SCIENTIST, DOUGLAS CDMO
The strategic implication is clear. These signals can be identified before confirmatory testing begins, allowing development teams to interrogate route selection and excipient strategy at a stage where adjustment remains feasible.
Bridget outlines a practical example. A team may initially select the hydrochloride salt of an API because it is more soluble. However, if nitrosation risk is heightened under acidic conditions, that choice may need to be revisited.
“We might have been planning to use the hydrochloride salt because it is more soluble. But if low pH increases nitrosation risk, we may consider switching to the free base form instead.”
Such decisions are rarely straightforward. Changing salt form can influence solubility, stability and product performance. These trade-offs are best resolved before formulations and processes are locked.
Regulatory evolution in nitrosamine risk assessment
Regulatory agencies have formalized acceptable intake (AI) limits for nitrosamine impurities, establishing daily exposure thresholds based on lifetime carcinogenic risk modeling. For many products, these limits fall in the low nanogram per day range, requiring control at parts per billion levels.
In the early stages, nitrosamines were largely treated as a single high-concern class. The presence of the functional group itself triggered stringent control expectations. This approach reflected limited data and a priority on patient safety.
As scientific understanding advanced, the regulatory approach evolved. The Carcinogenic Potency Categorization Approach (CPCA) introduced a structured method for assessing relative risk. Rather than applying uniform limits across all nitrosamines, regulators now consider the structural environment surrounding the nitrosamine moiety and its mechanistic potential to interact with DNA. AI limits are now assigned in proportion to predicted carcinogenic potency.
“Previously, all nitrosamines were treated as high risk. The new approach evaluates the chemical environment around the nitrosamine group and its likelihood of alkylating DNA. Not all nitrosamines pose equal carcinogenic risk,” says Bridget.
In one case managed at Douglas, an NDSRI was categorized in a lower potency group. The resulting AI limit allowed a targeted mitigation strategy that preserved product performance while maintaining patient safety.
Integrated control as a competitive advantage
For Douglas CDMO, nitrosamine control is not a discrete testing service; it is an integrated discipline that spans supplier oversight, formulation strategy, analytical capability and regulatory interpretation. It begins upstream, where vendor qualification is treated as a primary control point. At a high level, Douglas expects excipient and API vendors to address four core risk domains: the presence of nitrosating agents, including nitrite sources, the potential for nitrosatable amines within materials or manufacturing inputs, the use of recycled nitrogen-containing solvents, and cross-contamination risk on multipurpose equipment.
As Bridget explains: “For an organization like Douglas, a principal avenue of nitrosamine risk is vendor qualification. We bring in raw materials rather than manufacture them, so we require comprehensive nitrosamine risk assessments from suppliers.”
Analytical capability then supports targeted confirmation. Douglas employs validated liquid chromatography–mass spectrometry methodology with low parts per billion limits of quantification for nitrosamine impurities. Where an NDSRI is suspected, its molecular weight can be used to design a focused analytical approach.
As Bridget explains: “If we suspect a potential NDSRI, we can use its molecular weight to target it directly. If detected, we can often use the same method to study mitigation controls while maintaining the product’s critical quality attributes.”
For biotech companies selecting a CDMO partner, Bridget discusses three capabilities that should be prioritized. These include experience in conducting and defending nitrosamine risk assessments across raw materials and finished products, practical mitigation expertise in balancing safety and performance, and an analytical capability that supports informed decision making.
In her concluding remarks, Bridget captures the broader perspective succinctly:
“Nitrosamines represent a complex but intellectually rewarding challenge for analytical chemists. With structured risk assessment, proportionate mitigation, and strong analytical capability, they can be managed effectively within modern pharmaceutical development.”
Mastering the new standard of impurity control
Nitrosamines have become a benchmark for modern impurity control. When risk assessment, mitigation and analytical science are integrated into development, control becomes proactive rather than reactive. That is now the expectation across global markets – competitive advantage comes from managing this complexity with discipline.
For more information on how Douglas CDMO can support your next R&D project and assist with nitrosamine and other impurity controls, contact us.
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