Nitrosamines: from detection to understanding

The discovery of nitrosamine contamination in medicines transformed pharmaceutical quality systems almost overnight. Initial efforts focused on identifying affected products, understanding how contamination had occurred and implementing analytical methods capable of detecting trace levels of these highly potent impurities. Today, however, the challenge has evolved. Rather than responding to isolated contamination events, manufacturers are increasingly addressing nitrosamine drug substance-related impurities (NDSRIs), compounds that can form from the active pharmaceutical ingredient (API) itself during manufacture or storage.

While regulatory frameworks continue to evolve, the scientific challenge has also become significantly more complex. Unlike the relatively small group of simple nitrosamines that dominated the industry’s initial response, NDSRIs often have product-specific formation pathways, making them more difficult to predict, detect and control.

Andrew Teasdale – a leading expert in this field and Director, ATCMC Solutions – believes the industry has made significant progress over the past 12 to 18 months. Understanding of nitrosamine chemistry has improved, while structured workflows for drug substance and drug product risk assessment are helping manufacturers move beyond the reactive approaches that characterised the early years of the contamination crisis.

However, he also notes that NDSRIs represent a fundamentally different analytical challenge. While the formation of simple dialkyl nitrosamines can often be explained through established chemical mechanisms, NDSRIs result from a far more complex interaction between secondary amines, nitrosating agents and manufacturing conditions, making effective control considerably more difficult.

Detecting the presence of a nitrosamine is no longer enough”

This increasing complexity is changing expectations of analytical science. Detecting the presence of a nitrosamine is no longer enough. Laboratories must also demonstrate that analytical methods are sufficiently robust to distinguish genuine impurity formation from analytical variability, particularly when measuring concentrations at parts-per-billion levels.

Mayank Bhanti, Senior Director, USP, says manufacturers are encountering increasingly diverse nitrosamine structures and previously unrecognised formation pathways. Consequently, demand for reference standards has evolved rather than stabilised, while analytical methods require continual refinement. He also highlighted the importance of robust method validation, suggesting that artificially contaminated samples may provide a more representative assessment of recovery than conventional liquid spiking experiments.

Method development presents further challenges because no single analytical approach is universally applicable. Teasdale notes that sample preparation frequently varies between dosage forms, meaning methods developed for one product cannot necessarily be transferred directly to another.

Malcolm Rossi, Independent Consultant and member of the Novartis Nitrosamine Task Force, also points to the limitations of current analytical sensitivity. When monitoring extremely low concentrations of NDSRIs during stability studies, distinguishing genuine impurity development from normal analytical variation remains difficult, making confidence in long-term stability data an ongoing challenge.

To help alleviate this, Rossi cautions against the use of ultrasonic baths during sample preparation because of their potential to generate uncontrollable nitrite levels and introduce analytical artefacts. Bhanti meanwhile emphasises that careful validation and risk assessment remain essential to minimise analytical error and improve confidence in analytical results.

A broader lifecycle approach

The implications extend beyond the analytical laboratory. As understanding of nitrosamine formation improves, manufacturers are increasingly recognising that effective control depends as much on organisational competency as analytical capability. Rather than treating nitrosamines as an isolated quality control issue, companies are being encouraged to integrate risk assessment, formulation science, process understanding and regulatory expertise throughout the product lifecycle.

That broader perspective is echoed by Dr Archana Bahuguna, Regulatory Compliance Specialist, who argues that successful nitrosamine management depends on moving from reactive responses towards proactive quality systems. Rather than relying on confirmatory testing after potential issues have been identified, she advocates early risk categorisation across product portfolios by means of dedicated cross-functional teams capable of assessing chemistry, analytical science, manufacturing, toxicology and regulatory requirements together. She also highlighted common compliance failures, including inadequate risk assessment, insufficient analytical specificity and sensitivity, and weaknesses in cleaning validation – particularly as products move from laboratory development to commercial manufacture.

Nitrosamine control is increasingly viewed as a multidisciplinary challenge rather than solely an analytical one”

This reflects a broader shift in the industry’s thinking. Nitrosamine control is increasingly viewed as a multidisciplinary challenge rather than solely an analytical one. Analytical scientists remain central to identifying and quantifying impurities, but long-term success also depends on understanding how formulation, manufacturing processes, excipients, packaging and process changes influence nitrosamine formation. The result is the need for closer collaboration between functions that have traditionally worked more independently.

Regulatory complexity adds a further layer of difficulty. Although both the US Food and Drug Administration (FDA) and European regulators have established frameworks for nitrosamine risk assessment, differences remain in acceptable intake limits and implementation timelines. According to Bahuguna, there is currently no full convergence between FDA and European Medicines Agency (EMA) approaches, although the principles set out within ICH M7 are increasingly being adopted internationally. For manufacturers supplying multiple markets, this means regulatory strategies may need to accommodate different expectations until greater harmonisation is achieved.

Emerging technologies may help manufacturers manage increasing complexity. Computational tools and artificial intelligence are beginning to support risk prioritisation by helping identify products or manufacturing processes most likely to present a nitrosamine risk. However, these technologies should support rather than replace scientific expertise.

According to Bhanti computational approaches are becoming increasingly valuable for prioritising risk assessments, but they are not yet sufficiently standardised or transparent to be used in isolation. Instead, they should complement laboratory studies, process understanding and expert scientific judgement. As manufacturers generate more experimental data, these tools may become more powerful, but robust validation will remain essential before they can play a larger role in regulatory decision making.

For smaller manufacturers, developing this breadth of expertise presents a particular challenge. Rather than attempting to establish specialist nitrosamine capabilities immediately, it makes more sense to work with experienced contract research organisations and external experts while building internal knowledge. This approach allows companies to access specialist analytical capability without investing prematurely in complex infrastructure that may be difficult to sustain.

Future nitrosamine management - adaptability is key

Despite the scientific and regulatory progress made since the first nitrosamine-related recalls, nitrosamine control is unlikely to become a routine quality control exercise in the near future. The continuing evolution of NDSRIs, improvements in analytical science and increasing understanding of formation pathways mean manufacturers will need to adapt continuously as knowledge develops.

The industry’s response has therefore entered a more mature phase. The challenge is no longer simply detecting trace impurities but understanding the chemistry that drives their formation, selecting analytical methods capable of measuring them reliably and embedding that knowledge across product development and manufacturing.

As analytical capability continues to advance alongside regulatory expectations, success will increasingly depend on combining scientific understanding with effective collaboration across quality, manufacturing, analytical development and regulatory affairs. For manufacturers, the next stage of nitrosamine management will be defined not by a single analytical breakthrough, but by the ability to integrate multiple scientific disciplines into a coherent and evidence-based control strategy.

Article previously published in EPR’s ’What’s next for nitrosamines’ report. Read all articles in this report here.