How to mitigate nitrosamine risk with low nitrite excipients

51

Introduction
The pharmaceutical industry faces the difficult task of controlling and minimising nitrosamine impurities to acceptable levels across the entire drug supply chain. This is a significant challenge given that nitrosamine impurities can be introduced into drug products through multiple routes, including during the manufacture of APIs, the production and storage of formulated drug products, or even via the packaging materials used (6). Understanding the pathways to nitrosamine formation is key to developing appropriate mitigation strategies because it raises questions like, “Do I need to lower the risk at every stage?” and “Do I need to look at the influence of my API?” or “Is the excipient contributing to the risk?” Here are some of the approaches helping to lower contamination risk.

 

Diverse strategies for nitrosamine risk mitigation
There are many ways to approach a nitrosamine mitigation strategy, each tailored to the specific drug product and how it is manufactured. Potential options include, but are not limited to:

• Reducing one of the reactive species (vulnerable amine or nitrosating agent)
• Modifying the manufacturing process so that these reactive species do not encounter each other
• Altering the environment of the reaction, such as the pH or mobile phase
• Adding a nitrite scavenger to neutralize the nitrosating agent.

 

The addition of nitrite scavengers (or blockers) into formulations can effectively mitigate nitrosamine formation (7, 8), however, this is not a quick fix. The introduction of nitrite scavengers into a formulation comes with several hurdles that manufacturers must overcome. Drug developers need to confirm that the new formula is comparable to the original drug formulation in terms of its stability, safety and efficacy. To assess these attributes, analytical evidence is required, which can be extremely costly and time consuming.

 

Another option to consider is adjusting the pH of the formulation to minimise the risk of nitrosamine formation, as slightly acidic conditions have been shown to favour nitrosation pathways (9). Increasing the pH of a formulation, such as by using basic excipients, can limit the rate of nitrosamine formation in some formulations (9-11). However, this approach is limited to the pharmacological properties of the API, such as stability, dissolution and bioavailability, as these important properties could be altered by modifying the Ph (5).

 

Controlling nitrite concentration in a drug product that contains vulnerable amines is another means for reducing nitrosamine risk. However, this approach requires a case-by-case assessment. For instance, Moser et al., showed that conversion of nitrites to N-nitrosamine in a model formulation with a secondary amine was heavily dependent on the drug product processing steps (1). A tablet containing a secondary amine molecule (named Compound A2) made using wet granulation had about 2 times the nitrosamine compared to direct compression tablet (168 ppb vs 71 ppb, respectively, native nitrite levels from the formulation, measured after manufacturing). Upon storage at 40C/75% relative humidity for 4 weeks, that difference jumped 3 times, with the wet granulated product having 363 ppb compared to the direct compressed product having 121 ppb. The wet granulated product, with increased mobility of the reactive species, would need significantly less nitrites than the directly compressed product to stay below the acceptable daily intake levels for the N-nitroso-Compound A (depending on what is that value). Since nitrites often enter drug products through excipients, controlling the contribution of nitrites via excipients can be a valuable tool in the nitrosamine mitigation toolbox.

 

Considering the many different routes to possible nitrosamine formation, taking a holistic approach to mitigation is usually the best strategy – reducing risk from multiple directions across the drug development pipeline.

The role of excipients in nitrosamine formation
Excipients may not have the therapeutic power of an API, but they still have a big role to play in keeping pharmaceuticals safe. While excipients add negligible risk of directly introducing nitrosamines into a drug product, they can still be involved in their formation (12).To understand how, it’s important to consider how exactly nitrosamines are formed in the first place.

 

One route of nitrosamine development is the reaction between a vulnerable amine (including secondary and tertiary amines) and a nitrosating agent, such as nitrite (2). Under the right conditions, such as a slightly acidic environment, this combination can lead to the formation of nitrosamines (13). So, where do excipients come in?

 

Many common excipients may carry a nitrosating agent, in particular, nitrite. Nitrites are ubiquitous in nature and are therefore hard to avoid, especially in excipients derived from raw materials (13). This means that nitrite levels are detected in most pharmaceutical excipients (15). They can also be introduced into excipients during the manufacturing stage – e.g. from process water or a reaction by-product (13). As such, removing nitrites in excipients is not as simple as turning off a valve.

 

The nitrite content in excipients varies significantly. For instance, some excipients, like corn starch, are lower in nitrite concentration compared to others, such as crospovidone (15). Moreover, the nitrite content within a given excipient can vary between suppliers and even batches (15). Take crospovidone as an example; nitrite levels have been shown to range from 0.79 – 14 mg/g across various batches and five suppliers (15). The impact on nitrosamine formation is also dependent on the amount of excipient used in each formulation. For instance, magnesium stearate, although relatively high in nitrites compared to other excipients, is used in such small quantities (<1% of a formulation) that its impact can be minimal (15). Drug manufacturers looking to control nitrite levels in their formulations can consider using “low nitrite” versions of excipients on a case-by-case basis.

 

Low nitrite excipients: how do they work?
Low nitrite excipients cannot prevent nitrosamines from being formed during API manufacturing and storage. However, they can be used to remove one possible (but common) route of nitrosamine formation – the reaction between nitrites in excipients and vulnerable amines in a formulate drug product, such as on APIs – commonly referred to as N-Nitrosamine Drug Substance Related Impurities (NDSRI) (2). Recent studies reveal that 41.4% of APIs are potential nitrosamine precursors, with 14.7% containing a secondary amine, and most excipients contain the nitrosating agent, nitrite – indicating a risk for potential nitrosamine formation (11, 15). In these formulas, using low nitrite excipients is a simple and effective solution that could help to limit nitrosation of a susceptible API, avoiding possible unsafe levels in formulations (2). However, not all formulations need low nitrite excipients, because nitrites alone do not form nitrosamines. For example, if there is no vulnerable amine present in the drug product formulation or during drug product manufacturing, then the use of low nitrite excipients will not impact the risk of nitrosamine formation. It is also important to note that low nitrite excipients may not prevent nitrosamine formation caused by various nitrogen oxides from the atmosphere.

 

Manufacturers can trust the science-backed benefits of low nitrite excipients, with research confirming that they have been shown to reduce nitrosamines in model formulations by up to nearly 10-fold compared to excipients with average levels of nitrites (2). In addition, low nitrite excipients are compatible with various APIs and can be easily used alongside other strategies, such as nitrite scavengers, to form holistic nitrosamine prevention (16).

 

One study has demonstrated the effectiveness of using low nitrite excipients as part of a holistic approach to reduce the formation of N-nitrosodimethylamine (NDMA) – a common nitrosamine compound – in metformin (3). This is a widely prescribed drug for type 2 diabetes in which some batches from several manufacturers were found to exceed the maximum allowable intake of NDMA in 2019 (17).Specifically, the research demonstrated that limiting the nitrite contribution from excipients, particularly hydroxypropyl methylcellulose (HPMC), in combination with reducing residual dimethylamine (DMA) in the API – a nitrosamine precursor – was an efficient means to reduce NDMA in the final drug product to levels below the control threshold (3). Beyond nitrosamine risk reduction, low nitrite excipients present fewer regulatory hurdles and cost advantages compared to other strategies like reformulation.

 

Considerations for using low nitrite excipients
Drug developers may need to consider the possibility that the raw materials and manufacturing processes used to create low nitrite excipients could differ from excipients that are not low in nitrites. These material and manufacturing differences may impact the physical or chemical properties of the excipient. Like any material change in a formulation, excipient users must understand these differences, if any, to make risk-based decisions on switching to low nitrite excipients, and the impact that this might have on drug product performance.

 

If there is a requirement for control over nitrites within their formulation, manufacturers should assess the optimal approach for their formulations. This may include conducting tests on incoming materials, providing justification for no testing, or purchasing materials with nitrite assessments reported for each batch. Selecting an excipient partner with in-depth expertise can assist manufacturers in choosing the most suitable approach, thereby helping to ensure the safety of future drug formulations with low nitrite excipients.

 

5 key considerations for choosing an excipient partner
While excipient manufacturers are not obligated to guarantee low nitrite levels in their products, it is important for them to understand whether it is possible to control nitrites and, if so, how to control nitrites if a nitrite-related issue exists or were to occur. If manufacturers choose to control nitrite status of their excipients, there are several approaches they can consider. For instance, they could test every batch to ensure that they are meeting a pre-determined nitrite level or conduct regular audits to monitor nitrite content consistency. In addition, a comprehensive evaluation of manufacturing processes and potential nitrite contributors, supported by scientific principles, could be undertaken. Alternatively, a combination of these approaches could be employed.

If manufacturers choose to ensure low nitrite levels in their excipients, partnering with a company with expertise and strong capabilities in excipients can help drug developers confidently, quickly and easily incorporate low nitrite excipients into their formulations. It is recommended that formulators choose a partner that offers:

 

1. Support and guidance throughout the risk assessment and mitigation process. An experienced partner understands the complexities around validating and controlling nitrosamine risk and can provide science-based recommendations on the best approach to reduce contamination pathways.
2. Validated analytical methods to measure nitrites, offering customers peace of mind through the authentication that excipients are truly “low nitrite”. Not all nitrite analytical methods are equal. Each has its own advantages and drawbacks and the appropriate method needs to be selected for each excipient based on required sensitivity and, in some cases, available technology. For example, one study showed that using a highly selective system of ion chromatography coupled with mass spectrometry (IC/MS) overcame coelution issues of ion chromatography coupled with conductivity detection (IC/CD) to provide more accurate nitrite determination into the part per billion (18).
3. Comprehensive understanding of nitrite content in excipients, sources of nitrites and critical control strategies to ensure nitrite levels will remain below acceptable levels. Drug developers might not be nitrite experts themselves, so choosing a partner that can share this knowledge is crucial. It is important for these manufacturers to understand the excipient providers’ approach, including their methods for assessing nitrite content, how they acquire this data, the extent of nitrite control measures, and how they manage nitrite levels. Transparent information sharing between parties will aid in selecting a partner that matches a drug manufacturer’s needs.
4. Formulation expertise to ensure continued product compatibility, functionality and seamless integration when switching to low nitrite excipients.
5. Quality documentation will accelerate speed to market and the change control process – this involves evaluating, documenting and approving alterations to pharmaceuticals to ensure that the changes made do not negatively impact the end product (19).

 

REFERENCES AND NOTES

1. Moser J, Ashworth IW, Harris L, Hillier MC, Nanda KK, Scrivens G. N-Nitrosamine Formation in Pharmaceutical Solid Drug Products: Experimental Observations. J Pharm Sci. 2023 May;112(5):1255-1267.
2. Berardi A, Jaspers M, Dickhoff BHJ. Modeling the Impact of Excipients Selection on Nitrosamine Formation towards Risk Mitigation. Pharmaceutics. 25;15(8):2015 (2023).
3. Schlingemann J, Boucley C, Hickert S, Bourasseau L, Walker M, Celdran C, Chemarin T, Pegues C, Fritzsche M, Keitel J, Goettsche A, Seegel M, Leicht S, Guessregen B, Reifenberg P, Wetzel S, Müller T, Schooren F, Schuster T, Liebhold M, Kirsch A, Krueger P, Saal C, Mouton B, Masanes S. Avoiding N-nitrosodimethylamine formation in metformin pharmaceuticals by limiting dimethylamine and nitrite. Int J Pharm. May 25;620:121740 (2022).
4. Horne S, Vera MD, Nagavelli LR, Sayeed VA, Heckman L, Johnson D, Berger D, Yip YY, Krahn CL, Sizukusa LO, Rocha NFM, Bream RN, Ludwig J, Keire DA, Condran G. Regulatory Experiences with Root Causes and Risk Factors for Nitrosamine Impurities in Pharmaceuticals. J Pharm Sci. 2023 May;112(5):1166-1182.
5. Răzvan C. Cioc, Ciarán Joyce, Monika Mayr, and Robert N. Bream. Formation of N-Nitrosamine Drug Substance Related Impurities in Medicines: A Regulatory Perspective on Risk Factors and Mitigation Strategies. Organic Process Research & Development 27 (10), 1736-1750 (2023).
6. Nejc Golob, et al. Nitrocellulose blister material as a source of N-nitrosamine contamination of pharmaceutical drug products, International Journal of Pharmaceutics. 618: 121687 (2022).
7. Nanda KK, et al. Inhibition of N-Nitrosamine Formation in Drug Products: A Model Study. J Pharm Sci. 110(12):3773-3775 (2021).
8. Homšak M, et al. 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. Processes. 10(11):2428 (2022).
9. Ashworth, I. W.; Dey, D.; Dirat, O.; McDaid, P.; Lee, D.; Moser, J.; Nanda, K. K. Formation of Dialkyl- N -Nitrosamines in Aqueous Solution: An Experimental Validation of a Conservative Predictive Model and a Comparison of the Rates of Dialkyl and Trialkylamine Nitrosation. Org. Process Res. Dev. 2023.
10. Ashworth, I. W.; Dirat, O.; Teasdale, A.; Whiting, M. Potential for the Formation of N-Nitrosamines during the Manufacture of Active Pharmaceutical Ingredients: An Assessment of the Risk Posed by Trace Nitrite in Water. Org. Process Res. Dev. 2020, 24 (9), 1629– 1646.
11. Schlingemann J, Burns MJ, Ponting DJ, Martins Avila C, Romero NE, Jaywant MA, Smith GF, Ashworth IW, Simon S, Saal C, Wilk A. The Landscape of Potential Small and Drug Substance Related Nitrosamines in Pharmaceuticals. J Pharm Sci. 112(5):1287-1304 (2023).
12. The Role of Excipients in Determining N-Nitrosamine Risks for Drug Products. IPEC Position Paper. IPEC Federation (2022).
13. Control of Nitrosamine Impurities in Human Drugs (2021). Guidance for the Industry. FDA. Available at: download (fda.gov).
14. Wu, Y., Levons, J., Narang, A.S. et al. Reactive Impurities in Excipients: Profiling, Identification and Mitigation of Drug–Excipient Incompatibility. AAPS PharmSciTech 12, 1248–1263 (2011).
15. Boetzel R, Schlingemann J, Hickert S, Korn C, Kocks G, Luck B, Blom G, Harrison M, François M, Allain L, Wu Y, Bousraf Y. A Nitrite Excipient Database: A Useful Tool to Support N-Nitrosamine Risk Assessments for Drug Products. J Pharm Sci. 112(6):1615-1624 (2023).
16. Bayne AV, Misic Z, Stemmler RT, Wittner M, Frerichs M, Bird JK, Besheer A. N-nitrosamine Mitigation with Nitrite Scavengers in Oral Pharmaceutical Drug Products. J Pharm Sci. 2023 Jul;112(7):1794-1800.
17. Shohei Fukuda, Kanako Kondo, Shoji Fukumoto, Norimichi Takenaka, Osamu Uchikawa, and Itsuro Yoshida. Nitrosodimethylamine Formation in Metformin Drug Products by the Reaction of Dimethylamine and Atmospheric NO2 Organic Process Research & Development 27 (11), 2123-2133 (2023).
18. Koudi Z, Michael K, Barbara S, Markus M. Parts per billion of nitrite in microcrystalline cellulose by ion chromatography mass spectrometry with isotope labeled internal standard. Journal of Pharmaceutical and Biomedical Analysis, 235, (2023).
19. What is the purpose of change control? Freyr Solutions, 2023. Available at: Purpose of Change Control in Pharmaceutical Industry (freyrsolutions.com).