Nitrosamine Impurities: Risk Assessment, Testing and Control Strategies

Since the discovery of N-nitrosodimethylamine (NDMA) in certain angiotensin receptor blockers in 2018, nitrosamine impurities have become a major quality and regulatory concern across the pharmaceutical industry. Nitrosamines are classified as probable human carcinogens, and even trace levels in medicines can pose risk when exposure is prolonged. Recalls, supply disruptions and intensive regulatory scrutiny followed, and manufacturers worldwide were asked to review all marketed products. This white paper explains regulatory expectations for nitrosamine risk assessment, describes sensitive analytical methods and outlines mitigation strategies across API, excipients, process and packaging.

Background and Regulatory Landscape

Why Nitrosamines Matter

Nitrosamines are potent mutagens in many cases, classified in ICH M7 as a cohort of concern. Regulators have established acceptable intake (AI) limits, often at nanogram-per-day levels, based on carcinogenic potency data or structure-activity relationship approaches. Drug substance-related nitrosamine impurities, known as nitrosamine drug substance-related impurities (NDSRIs), have further complicated assessments because they have no existing toxicological data.

Regulatory Framework

Agencies including the FDA, EMA, Health Canada and others have issued guidance requiring manufacturers to conduct risk assessments, perform confirmatory testing where risk is identified, and report changes. Timelines for completion and expectations for updates have been communicated. The categorization approach for NDSRIs assigns potency categories based on structural features to determine acceptable intake limits.

Conducting a Nitrosamine Risk Assessment

Sources and Pathways of Formation

Nitrosamines form when secondary or tertiary amines react with nitrosating agents such as nitrites under certain conditions, typically acidic. Potential sources include:

• •API synthesis steps using amines and nitrite or azide reagents
• •Contaminated or recycled solvents, reagents and catalysts
• •Cross-contamination from shared equipment
• •Nitrite impurities in excipients
• •Degradation of drug substance during storage
• •Packaging materials such as nitrocellulose blister lidding

Risk Assessment Process

A structured assessment reviews the synthetic route, raw materials, solvents, equipment and cleaning, formulation excipients, packaging and storage conditions for each product. It should consider the entire supply chain, including information from suppliers and subcontractors. Findings are documented with a clear conclusion on whether a risk exists, and risks are prioritized for testing.

Supplier Engagement

Obtaining declarations and data from API and excipient suppliers is essential. Quality agreements should require notification of changes in manufacturing processes or materials that could introduce nitrosamine risk.

Analytical Testing Strategies

Sensitivity Requirements

Because acceptable intakes are very low, methods must quantify nitrosamines at low parts-per-billion levels relative to the drug substance or product. Regulators expect validated methods with appropriate limits of quantitation, typically at or below a defined fraction of the acceptable limit.

Techniques

LC-MS/MS and GC-MS/MS, often with high-resolution mass spectrometry, are the main techniques. GC-based methods suit volatile nitrosamines, while LC-based methods suit less volatile or thermally labile NDSRIs. Method challenges include matrix interference, artefactual formation of nitrosamines during sample preparation and ensuring selectivity. Preventing in situ formation, for instance by adding scavengers such as ascorbic acid during sample preparation, is important.

Method Validation

Validation follows ICH Q2 principles, demonstrating specificity, accuracy, precision, linearity and limits of detection and quantitation at relevant levels. Reference standards for nitrosamines, including custom synthesis for NDSRIs, are needed.

Mitigation and Control Strategies

Process Controls

Eliminating or reducing sources of nitrosating agents and secondary amines, modifying reaction conditions, adding quench or purge steps, and improving purification can reduce formation. Using higher-quality or alternative reagents and solvents, and avoiding recovered solvents unless controlled, helps.

Formulation Approaches

Antioxidants such as ascorbic acid and alpha-tocopherol have shown ability to inhibit nitrosamine formation in some products. Adjusting pH and selecting low-nitrite excipients can also help. Formulation changes require stability and bioequivalence considerations.

Packaging and Storage

Selecting packaging materials without nitrosating components and verifying that storage conditions do not promote formation protect product quality over shelf life.

Specifications and Ongoing Monitoring

Where risk persists, impurity specifications at or below the acceptable intake should be set, with routine testing or periodic verification justified by risk. Changes should be managed through change control and appropriate regulatory filings.

Regulatory Reporting and Communication

Manufacturers should be prepared to report confirmed findings and mitigation plans to authorities, adjust marketing authorizations and manage recalls if limits are exceeded. Transparent communication with healthcare professionals and patients, when needed, supports trust.

Building a Sustainable Program

• •Maintain a living risk assessment updated for process or supplier changes
• •Qualify analytical capacity internally or with expert laboratories
• •Train development, quality and procurement teams on nitrosamine risks
• •Incorporate nitrosamine evaluation into new product development from the outset

Conclusion

Nitrosamine impurities require a proactive, science-based approach combining thorough risk assessment, highly sensitive testing and well-designed mitigation. Organizations that embed nitrosamine control into their quality systems protect patients, maintain supply and demonstrate regulatory readiness.