FDA Workshop: Mitigation Strategies for Nitrosamine Drug Substance Related Impurities

Disclaimer: The following summary represents my perspective on some relevant points discussed during the event “Mitigation Strategies for Nitrosamine Drug Substance Related Impurities: Quality and Bioequivalence Considerations for Generic Products” organized by the FDA and the Center for Research on Complex Generics.

1. Purpose: The workshop aimed to address the risks associated with the formation of Nitrosamine Drug Substance Related Impurities (NDSRIs) in certain drug products. It focused on discussing strategies to mitigate these risks and considerations for evaluating the safety risks associated with NDSRIs.

2. Approaches for N-nitrosamine Formation Risk: Model Amine Systems were utilized to study the potential formation of nitrosamines in oral solid dosage (OSD) products. These studies helped identify important risk factors such as:

  • The vulnerability of amines based on pKa values,
  • The addition of water during processing (wet granulation),
  • The form of the amine (salt or free base), and
  • The physical stability of vulnerable amines (crystalline vs. amorphous).

Further details on this topic can be found in: J Pharm Sci . 2023 May;112(5):1255-1267 (https://jpharmsci.org/article/S0022-3549(23)00028-X/fulltext).

3. Reducing Nitrosamines Without Scavengers: A key assumption was made that the rate-limiting reagent in NDSRI formation is typically the trace levels of nitrite, rather than the more abundant amine in the active pharmaceutical ingredient (API):

  • Selecting excipients with low nitrite levels (0.04 to 0.1 ppm) can reduce nitrosamine levels by up to tenfold compared to initial formulations. For most formulations, this approach effectively lowers the risk below the limit of 178 ng/day for NDSRIs;
  • However, high-risk formulations may require additional mitigation strategies, such as transitioning from wet granulation to direct compression and incorporating nitrite scavengers to further reduce nitrosamines below the acceptable daily intake (ADI) limit of 18 ng/day.

4. Control Strategies for NDSRIs from Impurity Amines in APIs: The spatial location of nitrosation-susceptible amine impurities relative to the API can impact nitrosation kinetics. Controlling impurities in the final product is crucial in pharmaceutical manufacturing:

  • Crystallization is a key unit operation used to reject and control impurities, enhancing purity throughout the synthesis process;
  • The solubility-limited impurity purge (SLIP) test was employed to identify when an impurity forms its own pure solid phase during crystallization;
  • Applying SLIP tests and similar approaches to APIs helps understand the microspatial distribution of impurity amine precursors, which can differentiate the risk level for NDSRIs when changing API sources or implementing new processes.

For more information, refer to Org. Process Res. Dev. 2023, 27, 723−741.

5. Effectiveness of Antioxidants and Nitrite Scavengers: The effectiveness of antioxidants in mitigating NDSRI formation varied among selected model drugs:

  • Ascorbic acid > caffeic acid > and ferulic acid demonstrated the highest inhibition of NDSRI formation among the antioxidants tested;
  • The effectiveness of antioxidants depends on the drug substance, manufacturing, and formulation;
  • Increasing the concentration of antioxidants improved NDSRI mitigation;
  • Maintaining a neutral pH of the drug product served as a protective strategy against nitrosamine formation;
  • The formation of NDSRIs was more pronounced under conditions of elevated heat and moisture during the drying step of wet granulation.
  • Continuous manufacturing with direct compression may aid in nitrosamine mitigation.

Additionally, the removal of nitrite, a key reagent for N-nitrosation, is considered a promising strategy:

  • Nitrites can be present in water, APIs, excipients, and atmospheric NOx;
  • PABA (para-aminobenzoic acid) was identified as an efficient inhibitor of N-nitrosamine formation in pharmaceutical dosage forms and showed comparable activity to ascorbic acid and l-cysteine;
  • The selection of a nitrite scavenger should be carefully considered based on the amine structure, compatibility with the API and excipients, type of dosage form, and route of administration.

Additional information can be found in: Processes 2022, 10(11), 242.
(Processes | Free Full-Text | Assessment of a Diverse Array of Nitrite Scavengers in Solution and Solid State: A Study of Inhibitory Effect on the Formation of Alkyl-Aryl and Dialkyl N-Nitrosamine Derivatives)

Again, it’s important to note that not all points discussed during the workshop were included in the summary above.

I can explore those missed points in a future publication. The workshop covered a wide range of topics, including: additional mitigation strategies, analytical methods, regulatory considerations, and case studies, which deserve thorough attention.

What do you think?


My gratitude to you @lucas10mauriz for providing the brief summary!


The uptake of NOx from the atmosphere to increase the levels of nitrite seen in raw materials was something completely new to me. It could explain variations in results seen when testing batches at different times/labs, or batch to batch variation.
It also opens up a whole new area to consider for control, from those raw materials prior to use (storage etc. - though this should be covered by good GMP) to the potential to cause problems later down the line. Raw materials may be procured with very low levels of nitrite within them, but stages in the manufacture may then introduce increased nitrite levels. This may not manifest itself as nitrosamines immediately post manufacture but could lead to elevated levels forming on stability.
Something else to think about!

Differences in levels of nitrosamine formation between crystalline and amorphous forms of APIs, where the structure could change as part of the manufacturing process is also interesting to consider.


Dear @Pradpharma I appreciate your input, and I’m eager to continue discussing the topic of nitrosamines further.

Dear @MarkS, I found the discussion regarding “The uptake of NOx from the atmosphere” in the formation process of nitrosamines quite intriguing. It emphasizes the importance of being vigilant at every stage of the production process. I believe it is crucial to continue exploring and researching this topic to gain a comprehensive understanding of the potential risks and develop effective mitigation strategies.

Another highly interesting discussion revolved around the morphology of the API crystal. Crystal forms with higher surface area (the amorphous structure typically exhibits a larger surface area compared to the crystalline structure) or rougher surfaces may provide more opportunities for interactions with precursors of nitrosamines, potentially leading to their formation.

Therefore, it is essential for pharmaceutical manufacturers to carefully control and characterize the crystal morphology of APIs during the drug development and manufacturing processes.

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Fantastic reflections @lucas10mauriz

I would like to expand to call attention to Dr. Justin Moser presentation about using model amine systems to study the potential formation in oral solid dosage, some on his work was published back in May 2023

The data presented on the models proved that they could be used to estimate the formation of nitrosamines that may form via dialkyl amines (vulnerable amines). Using data such as Vulnerable amine molecular weight (MW), pKa, dose, dose/day, formulation %s, and Nitritie content; one can predict the formation of particular nitrosamines over the shelf life of the dosage form. Futhermore, the mode was designed to over-predict nitrosamines formation, where HNO2 degradation was ignored.


Details of the modeling can be found in the Ashworth et all publication.


Thank you @Naiffer_Host for your comment and the insightful retrospective you provided.

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Rapid formation of N-nitrosamines from nitrogen oxides under neutral and alkaline conditions

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Read papers from Larry Keefer and other nitric oxide exerts’ team, which is my old laboratory. My stay in NCI was spent mostly in looking for nitrosamines when materials were exposed to NO and air. That is why is every white paper I write, I mention NOx. Good to see the wheel being reinvented, I just hope it is not a square wheet. :slight_smile:


I want to focus on Dr. Grahek’s presentation. Nitrite in Lactose did not increase when exposed to the air. On the other hand, nitrite in starch increased at the same time. It’s amazing.

He hypothesized the difference in nitrite amount among excipients was due to the basicity of the excipient in the previous slide. I want to know the water content of the excipient used in this experiment.


Dear All

Requesting to provide the document for unknown NDSRS PDE for US ,which is 26.5 ng??

EDQM: Clearly mentioned 18 ng in Guideline.

Dear members,
Kindly access all the presentations from this workshop. Despite the EMA’s publication of the CPCA approach for NDSRIs, these presentations still offer valuable and scientifically relevant content for the assessment.