Nitrite-Driven Nitrosamine Formation in Pharmaceutical Systems: A Water-Mediated Risk Framework and Control Strategies

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Technical Review Article | Open Access | Published 29th September 2026

Nitrite-Driven Nitrosamine Formation in Pharmaceutical Systems: A Water-Mediated Risk Framework and Control Strategies

Santosh Bhende, Atul Phatak, Pravin Chaudhari - Department of Pharmaceutics, PES's Modern College of Pharmacy, Nigdi, Savitribai Phule Pune University, Pune, Maharashtra, India | EJPPS | 313 (2026)| https://doi.org/10.37521/ejpps31311

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Summary

N-nitrosamines are genotoxic impurities whose detection in several marketed medicines has raised major safety concerns for pharmaceutical systems. They form when nitrosating agents - particularly nitrite - react with amine precursors under favourable physicochemical conditions. This review examines nitrite-driven nitrosamine formation with an emphasis on water-mediated pathways in pharmaceutical systems. It outlines the underlying nitrosation chemistry, including classical acid-catalysed routes and alternative chloramine-mediated and oxidative mechanisms, and evaluates how water sources, water-purification processes and physicochemical parameters (pH, temperature and moisture) influence formation. Particular attention is given to how trace nitrite in pharmaceutical water systems generates nitrosamines even at very low concentrations. Analytical methods for nitrosamine and nitrite determination are reviewed, highlighting advances in LC-MS/MS, GC-MS and high-resolution mass spectrometry for ultra-trace quantification. Risk-based mitigations are discussed, including nitrite control, water-quality management, raw-material assessment, process optimisation and lifecycle monitoring. A key regulatory gap identified is the absence of defined nitrite limits for pharmaceutical water in pharmacopoeial standards. Overall, the review offers a mechanistic, risk-oriented framework for understanding nitrite- and water-related nitrosamine formation and argues for stricter, precursor-focused control measures to safeguard pharmaceutical product quality and safety.

Keywords: Nitrite, Nitrosation mechanism, Water-mediated reactions, Nitrosamine formation, Pharmaceutical water systems, Regulatory risk assessment

Introduction

N-nitrosamines are potent genotoxic impurities that have drawn intense scientific and regulatory attention because of their carcinogenic potential^1,2,3. The detection of N-nitrosodimethylamine (NDMA) and related nitrosamines in widely used medicines such as angiotensin II receptor blockers and ranitidine triggered global regulatory action and closer scrutiny of contamination-control practices^4,5,6. These events exposed the complexity of nitrosamine formation and the need to define its sources across the entire pharmaceutical lifecycle^2,3.

Nitrosamine formation typically involves reaction between nitrosating agents - chiefly nitrite - and secondary or tertiary amines under favourable physicochemical conditions^7,8,9. In classical chemistry, nitrite yields nitrous acid and reactive intermediates such as dinitrogen trioxide that drive N-nitrosation⁸. Recent work shows that formation can also proceed through alternative routes, including chloramine-mediated and oxidative pathways, so risk assessment must consider both direct and indirect mechanisms^10,11.

Although earlier emphasis fell on synthetic routes and excipients, water is increasingly recognised as an influential yet often overlooked participant. Water is not merely a solvent but a medium that promotes the transport, interaction and transformation of reactive species such as nitrite and amines, raising the probability of nitrosation^7,12. Trace nitrite in pharmaceutical systems is now established as a major driver of nitrosamine formation even at very low concentrations^13,12, and it can originate from raw materials, degradation, excipients and water⁷. Physicochemical parameters - pH, temperature and moisture - strongly modulate reaction kinetics and the stability of nitrosating species¹⁴. Despite advances in analytics and regulation, an important gap remains: neither the United States Pharmacopeia nor the European Pharmacopoeia specifies a nitrite limit for pharmaceutical water, although its role is well documented¹³. This review focuses on water-mediated mechanisms of nitrite-driven nitrosamine formation and integrates chemistry, analysis, mitigation and regulation into a risk-based framework⁶.

Chemistry and mechanisms of nitrosamine formation

Nitrosamine formation is governed by nitrosation reactions between nitrosating agents and amine substrates, strongly mediated by pH, temperature and reactivity^14,15,16. Nitrite is pivotal: in aqueous systems it is protonated to nitrous acid (HNO2), a key intermediate in equilibrium with dinitrogen trioxide (N2O3), an efficient agent that converts secondary amines to N-nitrosamines^15,16. Kinetics are highly pH-dependent. Mildly acidic conditions (about pH 3-4) favour HNO2 and N2O3 and promote nitrosation, whereas strong acidity over-protonates amines and reduces nucleophilicity, and neutral to alkaline conditions limit nitrosating species^8,14. Even so, radical-mediated and aldehyde-assisted routes indicate that formation can occur across broader conditions^7,8.

Secondary amines react directly to give stable N-nitrosamines, while tertiary amines generally require prior oxidative or hydrolytic dealkylation to reactive secondary intermediates^15,16. Electronic and steric features of the amine influence reactivity and formation rate^7,15. Water-treatment chemistry adds further pathways¹⁷: chlorination and chloramination form NDMA from monochloramine and dimethylamine or other amine precursors via unsymmetrical dimethylhydrazine-type intermediates^10,9, and these reactions are sensitive to pH, disinfectant dose and organic precursors¹⁰. Ozonation can convert nitrogen-rich organics into reactive intermediates that undergo nitrosation¹⁸. Because many nitrosamines are polar and water-soluble, aqueous diffusion enhances precursor contact and raises the probability of reaction at trace levels¹.

Water as a medium and source of nitrosating species

Water is a complex participant in nitrosamine formation, acting as solvent, reaction medium and a source of both nitrosating agents and precursors. Nitrite is the principal contributor, participating directly in nitrosation even at negligible concentrations^1,11; it can arise from source-water contamination, the environment, and in situ nitrate reduction by microbial or chemical routes¹. Although mildly acidic conditions favour nitrosating intermediates¹⁴, localised microenvironments - such as those in semi-hydrated solid dosage forms - can support nitrosation near neutrality through transient pH shifts and enhanced molecular mobility¹⁹. Sub-ppb nitrite has been reported to generate nitrosamines in the presence of reactive amines¹¹, underscoring the need to control water-borne precursors.

Water treatment has a dual effect, removing precursors yet sometimes generating them. Chloramination is a well-known route to NDMA^10,9; ozonation can transform nitrogenous organics into reactive intermediates^18,20; and ion-exchange resins may degrade to release amine precursors¹⁷. Activated carbon can promote surface reactions or incompletely remove precursors¹⁰, while reverse osmosis and nanofiltration remove dissolved impurities efficiently but can foul, indirectly favouring nitrite formation via nitrate reduction¹. Distillation yields high-purity water, yet storage and distribution can reintroduce trace precursors¹¹. Source-water composition varies with agricultural runoff, industrial discharge and geochemistry, altering inorganic nitrogen and dissolved organic matter²¹. Drinking-water nitrite limits set by the World Health Organization and equivalent regulations are far above the levels that can drive nitrosation in pharmaceutical systems, highlighting a gap between environmental and pharmaceutical requirements²². Municipal chloramination adds monochloramine that reacts with amine-bearing components to form NDMA⁹, affecting the feed water used pharmaceutically. Even after purified-water or water-for-injection treatment, trace nitrite may persist or be introduced downstream^11,7, so water should be assessed for reactivity as well as purity. The influence of common purification techniques is summarised in Table 1, and the regulatory status of pharmaceutical water types in Table 2.

Table 1. Influence of water purification techniques on nitrosamine formation risk

Water treatment technique	Primary function	Potential contribution to nitrosamine risk	Mechanistic basis
Chlorination / chloramination	Disinfection ^35,36	Formation of NDMA and related nitrosamines ^37,38	Reaction of chloramines with secondary/tertiary amines ^39,38
Ozonation	Oxidation of organic contaminants ^40,41	Formation of nitrosamine precursors, e.g. dimethylamine-derived species ^21,42	Oxidative transformation of nitrogen-containing compounds ^43,44
Activated carbon filtration	Removal of organic matter and disinfectants	Catalytic or surface-mediated reactions under certain conditions ^45,18	Adsorption/desorption and surface-catalysed transformations ^18,46
Ion exchange resins	Removal of ionic impurities ^47,48	Release of amine-containing compounds upon degradation ^1,18	Decomposition of quaternary ammonium functional groups ^1,18
Reverse osmosis / nanofiltration	Removal of dissolved impurities ^49,50	Indirect risk via membrane fouling or microbial activity ^51,52	Precursor accumulation ^53,51
Distillation	Removal of non-volatile impurities ^54,55	Minimal intrinsic risk; possible post-treatment contamination ¹²	Reintroduction via storage/distribution systems ^56,17

Table 2. Regulatory perspective on nitrite in water and its relevance to nitrosamine risk

Water type	Regulatory framework	Nitrite limit	Regulatory interpretation	Nitrosamine risk perspective
Potable water	World Health Organization; European Drinking Water Directive	WHO approx. 3 mg/L; EU approx. 0.5 mg/L ⁵⁷	Nitrite is a controlled impurity	Major upstream source of nitrosating agents
Purified water (PW)	United States Pharmacopeia; European Pharmacopoeia	Not specified	Controlled indirectly ^58,59	Trace nitrite possible; risk-based monitoring required
Distilled water	United States Pharmacopeia	Not specified	High purity expected	Low intrinsic risk; depends on storage/system
Water for injection (WFI)	United States Pharmacopeia; European Pharmacopoeia; FDA	Not specified	Stringent microbiological/endotoxin control	Very low nitrite expected; still relevant with amines
Sterile water for injection (SWFI)	United States Pharmacopeia	Not specified	Sterile packaged WFI	Minimal intrinsic risk

Nitrite as a critical determinant

Nitrite is among the most critical determinants of N-nitrosamine formation because it acts almost directly as a precursor to reactive nitrosating species²³. Protonation to nitrous acid and equilibrium with N2O3 enable conversion of secondary amines to N-nitrosamines, so that even small amounts contribute materially to the impurity burden^15,12,24. Reactivity is governed chiefly by pH⁵: moderate pH (3-4) maximises nitrosation, but chloramine-mediated and aldehyde-assisted routes allow formation near neutrality, revealing the limits of pH control alone^25,8. Critically, trace nitrite produces quantifiable impurities; reactions with susceptible amines yield detectable nitrosamines at sub-ppm and even ppb levels^24,26, and multiple low-level sources - water, excipients and degradation products - act cumulatively¹². In solid dosage forms, moisture- and pH-variable microenvironments create local conditions favouring nitrosation despite low bulk nitrite¹¹.

Nitrite enters pharmaceutical systems from water, excipients, active substances and environmental contamination; excipient nitrite content is a recognised, variable source^25,1. Processing amplifies its effect: higher temperature accelerates kinetics¹⁴, prolonged processing or storage allows reactions to proceed, and recycled process water can accumulate nitrite¹². Despite growing recognition in risk assessments^7,13, neither the United States Pharmacopeia nor the European Pharmacopoeia defines a nitrite limit for pharmaceutical water¹². Effective control of nitrite at every stage is therefore essential to minimise N-nitrosamine risk²⁴.

Analytical determination of nitrosamines and nitrite

The genotoxicity and very low acceptable-intake limits of nitrosamines demand highly sensitive, selective methods, often at parts-per-billion or parts-per-trillion levels^27,28. Gas chromatography-mass spectrometry (GC-MS) is widely used for volatile nitrosamines such as NDMA and offers high sensitivity for low-molecular-weight analytes, though thermal degradation at high injector temperatures can cause artefacts²⁹. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is preferred for complex pharmaceutical matrices, operating under milder conditions, reducing thermal degradation and resolving diverse nitrosamines including N-nitrosamine drug substance-related impurities (NDSRIs)^12,28; multiple reaction monitoring improves specificity and enables ultra-trace quantification. High-resolution mass spectrometry (HRMS) adds accurate-mass selectivity useful for screening novel nitrosamines and NDSRIs that targeted methods may miss^30,31,32.

Sample preparation is decisive: solid-phase extraction, liquid-liquid extraction and headspace analysis improve sensitivity and reduce matrix effects²⁹. Assessment of precursors - especially nitrite - is increasingly recognised as essential for pre-emptive risk management; ion chromatography and LC-based methods detect nitrite at trace levels¹³. Method validation for accuracy, precision, linearity, limit of detection (LOD) and limit of quantification (LOQ) is mandatory, and the diversity of nitrosamines drives multi-analyte and combined targeted/non-targeted strategies that detect known impurities while flagging new ones³⁰.

Mitigation strategies and regulatory considerations

Controlling nitrosamines requires a risk-based strategy that limits reactants and slows reactions through process design²⁵. Because even low nitrite triggers nitrosation with susceptible amines^7,25, water-quality management is central: pharmaceutical water systems should be designed and operated to minimise nitrite generation and accumulation, with ongoing monitoring of nitrite, nitrate and residual disinfectants^14,9. Raw-material control is equally important, since excipients and actives may carry nitrite or amine impurities; vendor qualification, material characterisation and impurity assessment help prevent precursor ingress^25,8. Process optimisation - controlling pH, temperature and residence time, avoiding acidic conditions where feasible, and segregating nitrosating agents from amines - reduces formation¹⁴. Nitrite scavengers and inhibitors offer an effective option where nitrite cannot be eliminated, subject to compatibility and safety evaluation. Because formation can continue in situ and on storage, lifecycle assessment and stability studies under relevant temperature and humidity are essential.

Global regulators, including the US Food and Drug Administration and the European Medicines Agency, expect documented risk assessments, source identification, mitigation and validated trace-level methods^27,11,33, consistent with ICH M7 principles for the assessment and control of mutagenic impurities³⁴. Regulatory guidance emphasises precursor control, yet the absence of pharmacopoeial nitrite limits for pharmaceutical water remains a significant gap that targeted monitoring and risk-based control must bridge. Major mitigation strategies are summarised in Table 3.

Table 3. Mitigation strategies for nitrosamine risk control.

Strategy	Approach	Impact on nitrosamine risk
Water purification	RO, distillation, activated carbon	Removes nitrite and precursors
Nitrite monitoring	Routine analytical testing	Early detection and control
Raw material control	Excipient/API screening	Prevents precursor introduction
Process optimisation	pH and temperature control	Reduces nitrosation kinetics
Segregation of processes	Separate amines and nitrosating agents	Minimises interaction
Nitrite scavengers	Ascorbic acid, antioxidants	Inhibits nitrosation reactions
In-line monitoring	Real-time detection systems	Immediate corrective action
Equipment cleaning	Cross-contamination prevention	Reduces precursor carryover
Storage control	Control humidity and temperature	Prevents delayed formation

Figure 1. Nitrite-driven N-nitrosamine formation in pharmaceutical systems: water-mediated mechanisms, risk assessment and control strategies — **Figure 1.** Nitrite-driven N-nitrosamine formation in pharmaceutical systems: water-mediated mechanisms, risk assessment and control strategies

Challenges and future perspectives

Several scientific and regulatory challenges persist. Formation under realistic, complex conditions is incompletely understood: alternative chloramine-mediated and oxidative pathways can operate near neutrality and depend strongly on water composition, precursor concentration and process conditions, complicating prediction^25,9. The lack of a defined nitrite limit for pharmaceutical water, together with variability from source water, treatment and system design, leaves risk assessment uncertain for amine-containing products^7,10,1. Analytical challenges remain around confident ultra-trace detection, matrix interference, robustness and inter-laboratory variability, and the need for simultaneous determination of multiple nitrosamines and precursors^30,12. In-product formation during storage - driven by residual nitrite, moisture and microenvironmental pH - further complicates predictive modelling and demands long-term stability evaluation. Water treatment's dual role as remover and potential generator of precursors, including material degradation that releases amines, requires deeper mechanistic understanding.

Looking ahead, predictive modelling that integrates chemical kinetics, water chemistry, process parameters and analytics - supported by in silico approaches - could identify high-risk cases and guide intervention¹⁶. Lower-leachable polymers and advanced adsorbents may reduce precursor introduction, while scientifically justified nitrite limits for pharmaceutical water and harmonised global expectations would strengthen risk management⁷. Real-time monitoring and process analytical technology could enable dynamic control during manufacture. Progress will require integrating mechanistic insight, modern analytics and regulatory harmonisation across disciplines.

Conclusion

Nitrosamine impurities are a complex, evolving challenge shaped by chemical reactivity, material variability and process conditions. Nitrite has emerged as a central determinant, particularly in aqueous environments where it readily generates reactive nitrosating species, and water functions as a dynamic medium that transports and transforms precursors rather than a mere solvent. Even trace nitrite from water, excipients or degradation can yield measurable nitrosamines under favourable conditions, and pH, temperature, moisture, treatment processes and system design all add complexity. The absence of explicit nitrite limits in pharmaceutical water specifications is a critical regulatory gap. Analytical advances have improved detection, but consistent ultra-trace quantification across complex matrices remains difficult. Effective mitigation requires an integrated, lifecycle approach combining water-quality control, raw-material management, process optimisation and real-time monitoring, with targeted control of nitrite across all sources. Predictive models, advanced analytics and harmonised, scientifically justified limits will be pivotal in strengthening nitrosamine risk management and ensuring the safety, quality and compliance of pharmaceutical products.

Abbreviations

NDMA - N-nitrosodimethylamine

N2O3 - dinitrogen trioxide

HNO2 - nitrous acid

GC-MS - gas chromatography-mass spectrometry

LC-MS - liquid chromatography-mass spectrometry

LC-MS/MS - liquid chromatography-tandem mass spectrometry

HRMS - high-resolution mass spectrometry

MRM - multiple reaction monitoring

SPE - solid-phase extraction

LLE - liquid-liquid extraction

IC - ion chromatography

LOD - limit of detection

LOQ - limit of quantification

NDSRI - N-nitrosamine drug substance-related impurity

IPEC - International Pharmaceutical Excipients Council

WHO - World Health Organization

FDA - US Food and Drug Administration

EMA - European Medicines Agency

RO - reverse osmosis

Funding: This research received no external funding.

Conflict of interest: The authors declare no conflict of interest.

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