Drawing a line: Where might the cohort of concern end?

Following up on the work that led to the cohort of concern arguments within Lhasa Limited’s Nexus platform, and material that I’ve repeatedly presented (first presented at the USP-LATAM workshop at the end of 2021, actually), we now have a paper just released in OPRD formalising the edges; which compounds are definitely not CoC?

This isn’t to say that everything that remains in the cohort is still potent; the SAR derisking of Thomas et al and Cross and Ponting is still critical, but those nitroso compounds that can’t form diazonium ions really shouldn’t be in the cohort…



Hello, my observations are thus, whereas:

  • the acceptable limits for nitrosamines translate into parts per billion in the drug products and their ingredients
  • the secondary amines present in the drug products are a levels vastly greater than ppb
  • the amount of nitrite (or other nitrosating agent) needed to exceed the acceptable limits is then also in the ppb range (especially for excipients which can be present in vastly larger quantities than the drug substance)

It follows that standard GMP practices cannot be successful in reducing the risks from nitrosating agents in excipients. At best GMP practices may control to ppm or just sub ppm levels.
And thus alternative practices will have to be found to reduce the overall risk to an acceptable level.


Congratulations for the great work @David & my dear friend Robert Foster :slightly_smiling_face:; phenomenal contribution by Lhasa Ltd. as always.
This is such a well articulated manuscript and the only way forward to mechanistically de-risk a significant category of N-nitrosamine impurities from SAR perspective. I was curious to know if the IQ consortium or Lhasa Ltd. is making an attempt to push this message through to the regulators.

@romnaiffer I believe this article should be placed in the list of Featured Topics


Happy to entertain your suggestion

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@AndyTeasdale I read in the publication that the article is part of the special issue ‘Nitrosamines: Challenges in Process Chemistry’ – where can we learn more about it? Thanks

Nice summary Iain, thank you!