On Friday 7th July 2023, the European Medicines Agency (EMA) released a major update on N-nitrosamine impurities in human medicinal products1,2 including a new approach on determining limits for N-nitrosamines. According to EMA, this approach is expected to contribute the management of products with nitrosamines while ensuring availability of the pharmaceutical drug supply.

The Q&A document1 outlines four approaches to support deriving Acceptable Intake (AI) limits for substances without carcinogenicity data: (1) a carcinogenic potency categorization approach (CPCA), (2) an enhanced Ames test, (3) the use of a surrogate based on SAR and read-across considerations, and (4) a negative result from an in vivo mutagenicity test.

The CPCA is outlined as a decision tree in which the N-nitrosamine impurity may be assigned to five potency categories based on its chemical environment. The CPCA is based on structure-activity relationship (SAR) concepts and it identifies structural features that directly increase or decrease the favorability of metabolic activation of nitrosamines (or that increase the clearance of the nitrosamine by other biological pathways). These structural rules consider the number of hydrogens on the α-carbon and the presence of additional deactivating or activating features. This information is used to assign an AI based on the potency category resulting from the nitrosamine structure. Five potency categories are defined with corresponding limits: potency category 5 (AI=1500 ng/day); potency category 4 (AI = 1500 ng/day); potency category 3 (AI = 400 ng/day); potency category 2 (AI = 100 ng/day); potency category 1 (AI = 18 ng/day).

The release also includes an updated list of acceptable intakes for established N-nitrosamines2 and a description of an enhanced Ames test for nitrosamine hazard identification.

Instem is currently engaged in providing functionality within the Leadscope Model Applier to support potency category calculations as well as read-across functionality to support the use of a surrogate based on SAR for derivation of AI limits.

If you would like to discuss these updates and solutions to consistently apply this updated information to N-nitrosamine impurities, please contact us (Kevin Cross, kevin.cross@instem.com).


  1. https://www.ema.europa.eu/documents/referral/nitrosamines-emea-h-a53-1490-questions-answers-marketing-authorisation-holders/applicants-chmp-opinion-article-53-regulation-ec-no-726/2004-referral-nitrosamine-impurities-human-medicinal-products_en.pdf
  2. https://www.ema.europa.eu/documents/other/appendix-1-acceptable-intakes-established-n-nitrosamines_en.pdf

Published by Glenn Myatt

Glenn J. Myatt is the co-founder of Leadscope and currently Senior Vice President, In Silico & Translational Science Solutions at Instem with over 30 years’ experience in computational chemistry/toxicology. He holds a Bachelor of Science degree in Computing, a Master of Science degree in Artificial Intelligence and a Ph.D. in Chemoinformatics. He has published 37 papers, 11 book chapters and three books.