You know, when I saw “who would have believed this,” I knew exactly who would have seen it coming, @ASrinivasan. You were saying this before anyone else.
The rest of us, not so much
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LOL! Jason,
I didn’t see this tsunami coming, though
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I never thought the day would come when we would have to be careful about even trace amounts of nitrous acid in the air. Even though secondary amines are said to be highly reactive, I thought that this only applied to homogeneous solutions…
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Nice observation! 
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It feels like everything was just about an amine and a nitrite and we had no idea! 
I never imagined I would get to experience medicinal/organic chemistry and toxicology in such a hands-on way, directly through real-world scenarios.
It’s also wonderful to see scientific knowledge being shared with people from all around the world. Huge thanks to the community for making these exchanges possible.
I’m truly happy to have met Yosuke, Naiffer, and so many others.
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Great question — and what a journey it’s been!
Looking back, one thing I wish I had known earlier is just how nuanced and complex the analytical challenges around nitrosamines truly are. There’s often a misconception that it’s just about developing a sensitive method and ticking a regulatory box. But in reality, it demands a deep understanding of chemistry, instrumentation and risk assessment.
For example, achieving the required sensitivity isn’t just about choosing the “right” LC-MS method — it’s about optimizing every detail: sample prep, injection volume, matrix effect mitigation, and even how you handle your solvents and labware. And then there’s the constant challenge of artifact formation during sample prep or storage — something I wish more people talked about openly.
I’ve learned there are no one-size-fits-all solutions. So my biggest takeaway is this: expertise matters — and we’re all still learning, together.
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I completely agree, Lucas. I am shocked that instrument manufacturers have not been recording record sales.
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If only I had know…
NOx in ambient air is a nitrosation source.
That there are several pharma unit ops which use large amounts of ambient air in direct contact with the drug product including fluid bed drying and tablet coating.
There are reports of very reactive 2ry amines undergoing nitrosation if just left in ambient air in the laboratory.
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dear Hermine
could you please share your opinion on how we should monitor the NOx limits in the mentioned facilities? is there any acceptable approach from authorities? any frequency etc?
BR
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I am a pharmacist by training. I’ve been working with nitrosamines.
I couldn’t agree more!
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Dear Eleni Politi, WO2025/004104A1 recommends using ionized air, becouse in several pharma unit ops which use large amounts of ambient air in direct contact with the drug product including fluid bed drying and tablet coating, risk Nox is very high. NDSRI content of the active pharmaceutical ingredients before and after exposure to the ionized air is different, after exposure to the ionized air concentration NDSRI lower, see below link. However, in guidelines I didn’t see any mentions about NOx.
I participated in Genotoxic, nitrosamine beyond (online) too and I asked this question to speaker (You participated too, YES?). I think I was able to be helpful.
Can Ionized Air in Pharma Pose a Risk of Nitrite Formation.pdf (926.1 KB)
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dear Hermine,
indeed it was a really informative summit thanks to great speakers!
As for NOx, EFPIA includes discussion on their potential contribution in nitrosamines formation (minor contributors). What’s more I trust, that air quality should be covered by GMP assessment.
Whats more, what it was discussed during the summit was that significant increase of nitrosamines due to air NOx has not been observed in industrial/ production scale, rather than small scale (plate) experiments.
I am sure that other colleagues join the USP NF have also attended the 9th Genotoxic, nitrosamine and beyond summit, so please share any additional feedback.
thank you
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@schlinjo1975 do you have any insight? I know you and the team have been looking carefully at this
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Dear @elenipoliti
Very interesting to hear that it was thought that NOx in the atmosphere was not a significant contributor to nitrosamine formation.
From my reading on the subject of nitrosamines over the past few years I find this a surprising position to reach, for a variety of reasons.
- When nitrosamines were discovered to be present in beer they formation was traced back to the formation of NOx during the drying processes involved. Direct heat with hot air was removed from the manufacturing process and the levels of nitrosamines in the beer dropped significantly.
- Presentations in recent years from excipient suppliers have identified that the source of the nitrites in these excipients is heavily influenced by the drying of the materials - absorption of the NOx gases into these raw materials.
- The paper that was published around the company that manufactured their product at 2 different sites, one in the countryside, with low air pollution (including NOx) and another one in a busy city with high air pollution. The nitrosamine levels across the 2 sites were significantly different, all other factors being equal, so significant that production had to stop at the city site, as the levels were too high.
- Anecdotal stories around certain batches of products having high levels of nitrosamines and investigations determining that there were unexpected local anomalies in NOx levels for that particular batch.
I would have thought that it might be easier for the level of NOx to increase on the factory scale, and be more difficult to reproduce on the smaller lab or pilot scale. The temperatures, volumes of air, and times required for drying a full scale batch may be such that there is the opportunity for the creation of NOx to then be absorbed by the product. The same potentially also true for spray coating, where there is also moisture involved, but maybe less so for the milling process, which is quicker, and drier.
I think that there is also some empirical data that has been presented previously that shows the levels of nitrosamine formed through the different stages of manufacture of a product, and where there are increases in the observed levels (fluid bed drying etc.) - but whether this is due to just the increase in temperature of those stages, or the presence of NOx has not been presented to date. However, I think that the patent included earlier in this thread indicates that the ionization of the air leads to a decrease in the levels of nitrosamine observed, which would suggest NOx as at least a significant cause, rather than just the heat and nitrites present in materials initially.
I would caveat all of this with the observation that every manufacturing process of every product, with different APIs, to form different nitrosamines behaves differently - and not always in a way that is predictable, unfortunately. What may be true for one product may not always be true for another.
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thank you for this detailed feedback. please don’t get me wrong. Perhaps I am mistaken too regarding what it was discussed during summit, and that’s why I called for further feedback 
.
However, I agree with point 3 for the study completed in Japan, but it referred to pollutant areas.
From my experience, quality of the compressed air, at the points of use that the air is going to be in contact with product, must conform with the requirements defined by the European Pharmacopeia as well as with the GMP requirements; oxides of nitrogen: NMT 2ppm.
however, as you said what works for one product may not work for another, so, perhaps this limit is high for other products, and I will note the “heads up”.
BR
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Dear colleagues
Мany studies have shown, that the NOx risk is higher in the case of inactive ingredients drying (fluid bed drying).I think the manufacturers of inactive ingredients should consider the risk NOx in their provide documentations, thereby facilitating the assessment of potential risks for drug products manufacturers.
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Hi @elenipoliti
I was at the Summit too. Next time we should have a short coffee talk 
Regarding NOx I talked with the colleague that presented the topic, and yes industrial scale is not the issue, unless, you are having a continious air flow that “refill” the NOx over and over again and that is what happens in a fluid bed dryer.
Additionally, that makes me think if testing of retention samples is a good idea, although, may represent a worst case in manufacturing (closing and opening of bags, etc.)
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Meeting in Vienna would have been a wonderful opportunity. I heard that other colleagues from USP_NF also joined the summit.
To ensure we don’t miss out on such opportunities in the future, perhaps we should plan this short (good) coffee talk withing the group
thank you also for your feedback. Encouraging to see that I have not missed anything
as for retained samples, at least from the regulatory point of view, we see that assessors love to go with the “worst case scenario” always so that option would cover all aspects (considering that results are robust and well within the expected trend).
Eleni
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Others have shown that NOx is a risk when using large volumes of air under promoting conditions (hot, humid): https://doi.org/10.1021/acs.oprd.3c00274. We are looking at the risk during storage. Our preliminary results are that blisters and screw-cap bottles provide good protection. Open storage is a risk as well. This applies to tablets, but also to analytical samples
NOx presentation FDA-CRCG Workshop NOV 2024 draft.pptx (11.3 MB)
Please take a look at our presentation for the 2024 FDA-CRCG Workshop.
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Dear colleagues.
Do we need to start considering air as an excipient?
(in particular for API manufacturing, Excipient manufacturing or manufacturing of tablets)