Guidance Breakdown: FDA Revises Its Final Guidance on Nitrosamine Impurities
Guidance Breakdown: FDA Revises Its Final Guidance on Nitrosamine Impurities
A newly revised guidance updates a previous version issued in February 2021 and includes some major changes. We break it down in this special free edition.
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The FDA has issued a revised final guidance helping manufacturers detect and control nitrosamine impurities in pharmaceutical products.
The guidance revises a previous version issued in February of 2021 (PDF) and includes some significant changes.
These changes include:
A new section on nitrosamine drug substance-related impurities (NDSRIs). (These novel nitrosamines were not addressed in the earlier guidance.)
Expanded information on the FDA’s August 2023 guidance establishing acceptable intake limits for NDSRIs.
Details on “two general structural classes of nitrosamine impurities: small-molecule nitrosamine impurities (nitrosamine impurities that do not share structural similarity to the [active pharmaceutical ingredient] API and are found in many different drug products) and NDSRIs that share structural similarity to the API and are generally unique to each API.”
New recommendations on implementing nitrosamine impurity control strategies.
Clarification on how manufacturers should assess test results to determine whether specifications for nitrosamine impurities are warranted, how to report revised specifications, when and how to contact the FDA, and recommended alternative approaches to establishing total nitrosamine impurity limits.
As with the older 2021 version of the guidance, this guidance recommends an acceptable intake (AI) limit of 26.5 ng/day for six types of small-molecule nitrosamine impurities that could be present in APIs or drug products.
They include:
N-nitrosodimethylamine (NDMA)
N-nitrosodiethylamine (NDEA)
Nnitrosomethylphenylamine (NMPA)
N-nitrosodiisopropylamine (NDIPA)
Nnitrosoisophenylethylamine (NIPEA)
N-nitrosodibutylamine (NDBA)
N-nitroso-N-methyl-4aminobutyric acid (NMBA)
For NDSRIs, the guidance recommends that manufacturers consult a new FDA resource page that includes updated information on recommended AI limits for certain NDSRI impurities based on their predicted carcinogenic potency categorization (CPCA).
The FDA also recommends that manufacturers consult its August 2023 guidance on NDSRIs.
We’ve broken down a few key points impacted firms should pay attention to.
Introduction and background
The FDA, working with international regulators, has been investigating nitrosamine impurities since 2018. These impurities have been found in drugs like angiotensin II receptor blockers, ranitidine, metformin, antibiotics, and varenicline.
The guidance describes conditions that may introduce nitrosamine impurities and recommends steps for manufacturers and applicants to detect and prevent unacceptable levels of nitrosamine impurities in drug products and APIs.
This applies to:
All chemically synthesized APIs
Drug products containing chemically synthesized APIs or fragments (including biologics with synthesized fragments)
Drug products at risk due to other factors described in the guidance
Semisynthetic and fermentation products at risk due to their structures
Nitrosamine impurities and the root causes of formation
Nitrosamines are a class of compounds with a specific chemical structure consisting of a nitroso group bonded to an amine (R1N(-R2)-N=O). They can form through a nitrosating reaction between amines (secondary, tertiary, or quaternary) and nitrous acid, typically derived from nitrite salts under acidic conditions.
These compounds are potent genotoxic agents in several animal species. Some nitrosamines are classified as probable or possible human carcinogens by the International Agency for Research on Cancer. The ICH M7(R2) guidance refers to them as "cohort of concern" compounds, recommending control at levels that would result in negligible human cancer risk.
The guidance identifies two main types of nitrosamine impurities:
Small-molecule nitrosamines: These do not share structural similarity to the API and can be found in many different drug products. Examples include N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), and others listed in Figure 2 of the guidance.
Nitrosamine drug substance-related impurities (NDSRIs): These share structural similarity to the API, having the API or an API fragment in their chemical structure. They are generally unique to each API and form through nitrosation of APIs (or API fragments) with secondary, tertiary, or quaternary amines when exposed to nitrosating compounds.
The guidance identifies the root causes of small-molecule nitrosamine impurities in APIs:
General conditions: Nitrosamines can form in the presence of secondary, tertiary, or quaternary amines and nitrite salts under acidic reaction conditions. The risk is higher if nitrous acid is used to quench residual azide in the presence of precursor amines.
Sources of amines: Amines can be present in the manufacturing process from various sources:
The API itself, its degradants, intermediates, or raw materials may contain amine functional groups
Tertiary and quaternary amines may be added as reagents or catalysts
Amide solvents (e.g., N,N-dimethylformamide) can degrade into secondary amines
Amine impurities in reagents or solvents
Vendor-sourced raw materials: Nitrosamines or precursors can be introduced through:
Impurities in fresh solvents
Nitrite impurities in starting materials or raw materials
Cross-contamination at manufacturing sites
Recovered materials: Solvents, reagents, and catalysts may pose a risk due to:
Residual amines
Nitrosamine formation during recovery processes
Inadequate cleaning between different materials or customers
Quenching process: Using nitrous acid to decompose residual azide directly in the main reaction mixture can lead to nitrosamine formation if it contacts residual amines.
Lack of process optimization and control: Inappropriate or poorly controlled reaction conditions (temperature, pH, reagent addition sequence) can contribute to nitrosamine formation.
Nitrosamine impurities in drug products from sources other than APIs
The guidance also explains nitrosamine impurities in drug products from sources other than APIs. Specifically:
Nitrite impurities are common in many excipients at parts per million levels, which may lead to nitrosamine formation during drug product manufacturing or storage.
Nitrite and nitrosamine impurities may be present in potable water used in manufacturing.
Container closure systems, secondary packaging components, and manufacturing equipment could be sources of nitrite or nitrosamine impurities that leach into drug products.
In terms of root causes in drug products other than APIs, NDSRIs can be generated during drug product manufacturing or storage over its shelf life.
The main root causes stated are:
Nitrosating impurities (e.g., residual nitrite in excipients) leading to nitrosation of the active ingredient.
NDSRIs carried over from APIs.
The guidance warns that NDSRI formation is more common in drug products than APIs because it often results from a reaction between the API or API fragment and nitrite impurities in the drug product — and NDSRI levels may increase during storage. Drug products with APIs containing secondary, tertiary, or quaternary amine groups are considered at risk for NDSRI formation if exposed to nitrosating agents.
Recommendations for controlling and mitigating nitrosamines
Acceptable Intake (AI) limits
The guidance bases AI limits on the ICH M7(R2) guidance, defining them as levels that approximate an increased cancer risk of one additional case in 100,000 subjects over a lifetime (70 years) of daily exposure.
The FDA recommends several specific approaches for determining AI limits:
Using the predicted Carcinogenic Potency Categorization Approach when robust carcinogenicity data is unavailable.
Database and literature searches for available carcinogenicity and bacterial mutagenicity data.
In vivo and/or in vitro testing using the specific compound.
Read-across analysis from a structurally similar surrogate with robust carcinogenicity data.
If the AI limit cannot be determined using these approaches, the FDA recommends using 26.5 ng/day as the default AI limit.
For drug products containing multiple nitrosamines, the total limit should not exceed the recommended AI limit for the most potent nitrosamine present. The guidance also provides an alternative flexible AI limit approach for cases where multiple nitrosamines are present, as described in Appendix C.
The FDA’s recommended three-step mitigation strategy
The guidance outlines a three-step strategy for API and drug product manufacturers and applicants:
Assess the risk of nitrosamine impurities in APIs, marketed products, and products under approved and pending applications. Risk assessments should be conducted in a timely manner based on the prioritization of drugs.
Perform confirmatory testing when there is any risk for the presence of nitrosamine impurities. The analytical methods should have specificity, excellent chromatographic separation, and highly sensitive detection capability.
Report changes implemented to prevent or reduce nitrosamine impurities in APIs and drug products to the FDA. This includes submitting DMF amendments and changes to approved or pending applications as required by FDA regulations.
Recommendations for API manufacturers
The guidance provides detailed recommendations for API manufacturers to mitigate and control nitrosamine impurities throughout manufacturing, emphasizing the importance of process optimization, supply chain management, and rigorous testing protocols.
To mitigate the presence of nitrosamine impurities in APIs, the FDA recommends API firms take several steps:
Optimize the design of the manufacturing process during route of synthesis (ROS) development to minimize or prevent nitrosamine formation.
Consider factors such as avoiding reaction conditions that may produce nitrosamines, using alternatives to amine bases, avoiding amide solvents when possible, replacing nitrites with other quenching agents, and optimizing reaction conditions.
Remove quenching steps from the primary reaction mixture to reduce nitrosamine formation risk.
Audit supply chains and monitor for at-risk API raw materials and intermediates.
Use recovered materials only in the same step or earlier steps of the same process to avoid cross-contamination.
Analyze water used in API manufacture for nitrites and nitrosamines and use purified water if necessary.
Eliminate sources of nitrosamine impurities introduced through exogenous sources when possible.
Oversee any reprocessing or reworking of API batches to control nitrosamine impurity levels.
The FDA also identifies specific steps API firms should take to control nitrosamine impurities in APIs:
If a nitrosamine impurity is detected above the limit of quantitation (LOQ), develop a strategy to ensure the level remains at or below the recommended AI limit.
For at-risk APIs with an impurity detected above 10% of the recommended AI limit, test each batch on release and stability samples for nitrosamine impurities.
Develop an appropriate control strategy considering batch-to-batch variations.
Do not release any API batch containing levels of nitrosamine impurities above the recommended AI limit for distribution.
Implementing recommended AI limits
Assessing test results
The guidance recommends following the three-step mitigation strategy here:
Conduct a risk assessment to determine if a drug product is at risk of nitrosamine formation.
If risk is identified, perform confirmatory testing to determine if the drug product contains nitrosamine impurities.
Confirmatory testing should be performed on at least three representative batches.
Then, based on the results, manufacturers and applicants should take the following actions:
If nitrosamine levels are ≤10% of the recommended AI limit:
No specification (method and acceptance criterion) is needed. (This applies only if the root cause is well understood and manufacturing process controls are established and validated.)
Nitrosamine levels should be reevaluated during process validation studies and throughout the product life cycle.
For approved drug products, results can be included in the annual report.
If nitrosamine levels exceed 10% of the recommended AI limit but are within the limit:
Establish a control for nitrosamines in the release and stability specifications.
For approved drug products, submit this information in a supplement as changes being effected in 30 days.
If nitrosamine levels exceed the recommended AI limit:
Implement changes in formulation, manufacturing process, or packaging to ensure levels remain within the recommended AI limit.
For approved drug products, submit a prior approval supplement for major changes.
Recommended timeline for implementation
Approved or marketed drug products
Small-molecule nitrosamine impurities:
Complete risk assessment by March 31, 2021
Conclude confirmatory testing and submit required changes by October 1, 2023
NDSRIs:
Complete risk assessment by November 1, 2023
Conclude confirmatory testing and submit required changes by August 1, 2025
Drug products in development and under FDA review
Assess the risk of nitrosamine impurities as early as possible in development, preferably before in vivo tests like bioequivalence studies.
Conduct risk assessment and perform confirmatory testing before submission of original application when feasible.
If not available at time of submission, submit risk assessment and confirmatory testing results in an amendment as soon as possible.
Reporting changes to mitigate nitrosamine impurities
API Manufacturers:
Submit amendments to the drug master file (DMF) for process changes.
Inform each drug product manufacturer or applicant referencing the DMF.
Report changes in the application if API is manufactured by the applicant.
Drug Product Reformulation:
Generally requires submission of a prior approval supplement for approved products.
Provide stability data to support reformulated drug products:
For approved products, submit three months of accelerated and long-term stability data at supplement submission.
The FDA may request six months of accelerated stability data if there's potential for increasing NDSRI levels.
Bioequivalence (BE) considerations:
Typically requires in vivo BE study for reformulations.
The FDA provides alternative approaches for demonstrating BE in certain cases based on BCS classification and type of reformulation.
Comparative dissolution testing may be sufficient in some cases.
Maintaining the drug supply
Manufacturers and applicants should contact the FDA's Drug Shortage Staff if changes or recalls may disrupt the drug supply. The FDA states that it can work with manufacturers and applicants to mitigate nitrosamine risks while avoiding supply interruptions — and may recommend interim AI limits for temporary periods to prevent drug shortages.
Each circumstance is evaluated on a case-by-case basis.
The FDA may work directly with specific manufacturers or applicants and consider whether to recommend an interim AI limit.
The FDA generally does not intend to object to distributing drug product batches with nitrosamine levels at or below recommended interim AI limits during specified periods under certain circumstances.
FDA will post recommended interim AI limits on the nitrosamine guidance web page.
Key takeaways from the guidance
All manufacturers should evaluate nitrosamine risks in their products.
This applies to all chemically synthesized APIs, drug products containing chemically synthesized APIs or fragments, and products at risk due to other factors described in the guidance.
Manufacturers and applicants should conduct risk assessments for both small-molecule nitrosamines and NDSRIs.
Risk assessments should be prioritized based on factors such as maximum daily dose, duration of treatment, therapeutic indication, and number of patients treated.
The guidance recommends specific timelines for completing risk assessments for approved and marketed products and for products in development.
Implement detection, control and mitigation strategies as needed.
If a risk is identified, confirmatory testing should be performed using sensitive and appropriately validated analytical methods.
Manufacturers should develop control strategies if nitrosamine impurities are detected above the limit of quantitation (LOQ).
Mitigation strategies may include optimizing manufacturing processes, removing quenching steps from main reaction mixtures, auditing supply chains, controlling the use of recovered materials, and analyzing water for nitrites/nitrosamines.
For drug products, strategies may include screening excipients for nitrite impurities, incorporating antioxidants, and modifying the formulation's microenvironment to neutral or basic pH.
Work with the FDA to report changes and address any issues found.
Changes implemented to prevent or reduce nitrosamine impurities must be reported to FDA in accordance with applicable regulations. This includes submitting DMF amendments, changes to approved applications, and amendments to pending applications.
For approved products, the type of submission (e.g., prior approval supplement, changes being effected in 30 days) depends on the nature and extent of the changes.
Manufacturers should contact the FDA if batches exceeding AI limits are already in distribution or if they are considering adopting AI limits different from FDA recommendations.
Balance risk mitigation with maintaining critical drug supplies.
The guidance recognizes the need to address nitrosamine impurities while avoiding interruptions in drug supply. Manufacturers and applicants should contact the FDA's Drug Shortage Staff if changes or recalls may disrupt supply.
FDA may recommend interim AI limits for temporary periods to prevent shortages.
Each case is evaluated individually, and FDA may work directly with manufacturers to find solutions that protect patient health while maintaining drug availability.
The agency may exercise enforcement discretion in certain circumstances to prevent or mitigate drug shortages.
Our recommendations
Here’s a look inside our emerging playbook for nitrosamine mitigation and control.
Drive nitrosamine mitigation and control into your risk management program. There’s no way around the fact that a robust risk assessment program will be the foundation of effective nitrosamine control. This involves systematically evaluating every product, API, and excipient in your portfolio for nitrosamine risk. We recommend creating a centralized database that captures key information such as amine content, potential nitrite sources, and critical process parameters. Then, assign risk scores based on factors like daily dose, duration of treatment, and patient population. Prioritize high-risk products for immediate action while establishing a schedule for periodic reassessment of all products. This approach allows you to allocate resources more effectively and identify potential issues before they become critical. Remember to update your evaluations as new scientific information becomes available or when changes occur in your supply chain or manufacturing processes.
Consider investing in high-sensitivity equipment like triple quadrupole LC-MS/MS systems capable of detecting nitrosamines in the low parts per billion range. Given the low levels at which nitrosamines can pose a risk, many firms will have a strong case for upgrading their analytical capabilities. In addition to system upgrades, also consider:
Developing and validating methods that are specific to your products and can differentiate between various nitrosamine species.
The matrix effects of different formulations and how to make sure your methods are robust across various product types.
Training your analytical staff on these specialized techniques and participating in inter-laboratory comparison studies to ensure the accuracy of your results.
Optimize your manufacturing processes to prevent nitrosamine formation. The best way to mitigate nitrosamines is to prevent them from forming in the first place. We suggest conducting a step-by-step analysis of each of your processes to identify potential points where nitrosamine precursors could be introduced or where conditions might favor their formation. Then, put in place in-process controls at these critical points, such as continuous monitoring of pH, temperature, and potentially even real-time nitrosamine detection. Some firms may want to go as far as to redesign processes to eliminate high-risk steps, such as replacing nitrite-based reagents or modifying quenching procedures. Consider if there’s value in developing and validating purge studies to demonstrate consistent removal of potential nitrosamines or their precursors. Remember that even minor changes in process parameters can impact nitrosamine formation, so maintain tight control and thorough documentation of all manufacturing conditions.
Be proactive in your regulatory strategy moving forward. Given that nitrosamine regulations are evolving, firms may want to develop a regulatory roadmap for each product outlining required submissions and timelines based on the FDA guidance. Don't just aim for minimum compliance — consider how you can exceed expectations and demonstrate industry leadership in nitrosamine control. Engage in early and frequent communication with regulatory authorities, especially for complex cases or novel mitigation strategies. Prepare robust data packages that address current requirements and anticipate potential questions.
Implement robust change management. In the context of nitrosamine control, even seemingly minor changes can have an outsized impact. Review and, if necessary, revise your change control procedures to explicitly consider nitrosamine risks for any proposed change, whether it's in raw material sourcing, manufacturing process, or product formulation. We advise developing a standardized checklist or decision tree to evaluate the potential impact of changes on nitrosamine formation or control. Importantly, make sure that your change management process includes appropriate analytical testing to verify that changes haven't inadvertently increased nitrosamine risk. Consider implementing a staged approach for significant changes, with increased monitoring during initial implementation. Remember that change management extends beyond your immediate operations — changes at your suppliers can also impact nitrosamine risks, so ensure your supplier agreements require notification of relevant changes.
Where outside RA/QA support will be valuable
In light of this guidance, several specialized projects and types of support are well-suited for external support and guidance from a qualified consultant. Here are some specific areas where we’re planning to support teams around nitrosamine control and mitigation in light of this guidance:
Conducting a thorough gap analysis between current practices and FDA guidance requirements and developing a detailed remediation plan.
Conducting a portfolio-wide nitrosamine risk assessment.
Developing and validating highly sensitive nitrosamine detection methods.
Developing a regulatory roadmap and prepare necessary submissions (e.g., prior approval supplements, DMF updates).
Conducting a comprehensive review/audit of manufacturing processes to identify and mitigate nitrosamine formation risks.
Developing and implementing an enhanced supplier qualification program focused on nitrosamine risks.
Developing and delivering comprehensive nitrosamine awareness and control training for staff.
Investigating nitrosamine detections or out-of-specification results and developing comprehensive CAPAs.
Developing and implementing enhanced change management procedures specifically addressing nitrosamine risks.
Designing and implementing an enhanced stability program incorporating nitrosamine monitoring.
Here are just a few questions for self-assessment to understand if an RA/QA consultant would be valuable to your firm in navigating nitrosamine concerns. Talk to us if you don’t know or aren’t satisfied with your answers to any of them.
Do we have the in-house analytical capabilities to detect and quantify nitrosamines at the low levels required by the FDA guidance? Consider your in-house ability to achieve the necessary limits of detection/quantification, validated methods for all relevant nitrosamine species, and expertise in interpreting complex analytical data.
Can we confidently assess the nitrosamine formation risk across our entire product portfolio and supply chain within the timelines specified by the FDA? Consider the breadth of your product types, complexity of supply chains, and depth of understanding of nitrosamine chemistry in various manufacturing contexts.
Are we fully prepared to engage with the FDA on nitrosamine-related issues, including developing comprehensive regulatory strategies and preparing robust submission packages? Do you have experience in negotiating complex quality issues with regulators and the ability to craft compelling scientific arguments?
Do we have a systematic approach to evaluating the impact of manufacturing changes, reformulations, or new product developments on nitrosamine risk? Think about integrating nitrosamine considerations into existing change management processes and your ability to perform risk assessments on novel formulations or processes.
Can we effectively manage and mitigate nitrosamine risks in our global supply chain, including conducting specialized audits and implementing enhanced supplier controls? Consider outside resources for expanded supplier oversight, expertise in nitrosamine-specific audit protocols, and evaluating diverse manufacturing practices across different geographies.
The bottom line: In light of nitrosamine risks, manufacturers and applicants must take proactive steps to evaluate their products, implement robust analytical methods, optimize manufacturing processes, and enhance supplier oversight. The guidance provides specific timelines for risk assessments and remediation actions, emphasizing the urgency of addressing this issue. Successfully navigating these requirements will require a thorough understanding of nitrosamine chemistry, advanced analytical capabilities, and a proactive approach to regulatory compliance. As scientific understanding of nitrosamine impurities continues to evolve, firms should be prepared for ongoing engagement with the FDA and potential updates to their control strategies.
The FDA is implementing this guidance without prior public comment as “prior public participation is not feasible or appropriate.”
Talk to us
Need expert support in addressing nitrosamine impurities in your drug products and aligning with FDA expectations? Contact us to access our exclusive pool of 2,500+ global consultants, 255+ of whom are former FDA.
Our experts can assist you with:
Conducting comprehensive nitrosamine risk assessments across your product portfolio.
Developing and validating highly sensitive nitrosamine detection methods.
Optimizing manufacturing processes to minimize nitrosamine formation.
Enhancing supplier qualification and auditing programs for nitrosamine control.
Preparing regulatory submissions and developing strategies for FDA engagement.
Implementing robust change management processes that address nitrosamine risks.
Training your team on nitrosamine chemistry, detection, and control strategies.
Staying current with evolving scientific understanding and regulatory expectations for nitrosamine impurities.
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