🇨🇦 Health Canada updated the guidance and Appendix 1(March 15, 2024)

What’s new

March 15, 2024: An updated version of the Guidance on nitrosamine impurities in medications has been posted online.
Several updates to General and Quality-related topics have been incorporated into the guidance document, including:

  • when the submission of confirmatory testing results is not expected (i.e., for nitrosamine impurities in Appendix 1 (formerly Appendix 2) that are classified as non-mutagenic) (number 3),
  • managing and submitting Step 3 changes to the market authorization relating to risk mitigation measures, including several additional changes that can be implemented as Level III - Annual Notifications (number 13 and Appendix 2 (formerly Appendix 1)), and
  • acceptable limits of quantitation for analytical procedures (number 33).

Those sections that have updated from the previous version are identified with the descriptor “updated”.

Of note, Health Canada’s table of established Acceptable Intake (AI) limits (formerly Appendix 2) has been renumbered to Appendix 1, removed from the guidance document and placed in a tab on Health Canada’s nitrosamines webpage. These changes are to enable a more timely update to the listing of established AI limits. In addition, to facilitate searching an AI limit for a N-nitrosamine impurity, the tab contains a table that can be filtered and a spreadsheet that can be downloaded. Additional AI limits for several nitrosamines that are considered acceptable to Health Canada are included in the update. The AI list can be filtered by date to identify the most recent additions.


19 compounds are newly included in the latest Appendix 1.

  • N-nitroso-2-(7-methoxy-1-naphthyl)-N-[2-(7- methoxy-1-naphthyl)ethyl]ethylamine (in Agomelatine) : 100ng/day
  • 1-(2,3-dichlorophenyl)-4-nitrosopiperazine (in Aripiprazole): 400ng/day
  • N-nitroso-desmethylazelastine (in Azelastine): 100ng/day
  • 2-[benzyl(nitroso)amino]benzoic acid (in Benzydamine): 1500ng/day
  • N-nitroso-betaxolol (in Betaxolol): 1500ng/day
  • 1-(2-ethoxyethyl)-2-(1-nitrosopiperidin-4-yl)-1H-benzo[d]imidazole (in Bilastine): 400ng/day
  • N-nitroso-bumetanide (in Bumetanide): 1500ng/day
  • N-nitroso-dabigatran etexilate (in Dabigatran etexilate): 1500ng/day
  • 5-chloro-4-methyl-2-[(2S)-2-methyl-1-nitrosopyrrolidin-2-yl]-1H-benzimidazole (in Daridorexant): 1500ng/day
  • N-nitroso-landiolol (in Landiolol): 400ng/day
  • N-nitroso-folinic acid (in Leucovorin): NMI
  • N-nitroso-N-desmethyl-mirtazepine (in Mirtazapine): 400ng/day
  • N-nitroso-palbociclib (in Palbociclib): 400ng/day
  • 1-(2-methoxyphenoxy)-3-(4-nitrosopiperazin-1-yl)propan-2-ol (in Ranolazine): 400ng/day
  • N-(2,6-dimethylphenyl)-2-(4-nitrosopiperazin-1-yl)acetamide (in Ranolazine): 400ng/day
  • N-nitroso-ribociclib (in Ribociclib): 400ng/day
  • N-nitroso-N-desmethyl-sildenafil (in Sildenafil): 400ng/day
  • (4-nitrosopiperazin-1-yl)(tetrahydrofuran-2-yl)methanone (in Terazosin): 400ng/day
  • N-methyl-N-((3R,4R)-4-methyl-1-nitrosopiperidin-3-yl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine (in Tofacitinib): 400ng/day

Plabociclib is generally considered for advanced cancer. I doubt why did agency suggested AI of 400 ng/day resulting 3.2 ppm for N-nitroso palbociclib when it can be simply allowed up to ICH Q3A levels of 1500 ppm!!


Ribociclib is generally considered for advanced cancer.hence it can be simply allowed up to ICH Q3A levels

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It seems N-nitroso-lidocaine EP Impurity E was removed from the limit list as well. This nitrosamine previously had CPCA category 4 - 1500 ng/day assignment by Health Canada in the 24 July 2023 and 20 October 2023 guidance. Now it seems the entry was kept (without changing the date) but the nitrosamine was changed to N-nitroso-desethyl-lidocaine (CPCA category 2) (which is also listed by TGA and EMA).

guidance-nitrosamine impurities-medications October 2023.pdf (1.2 MB)
guidance-nitrosamine impurities-medications-eng.pdf (1.7 MB)

I assume this a mere procedural correction/alignment or a redacting error and not linked to discussions on the deactivating effect scoring for the β-amido group (or the deactivating feature of long chain on both sides of the nitroso bond) or new biological data:

N-nitroso-lidocaine EP impurity E

  • Alpha-hydrogen score 1
  • Activating feature “chain on both sides” +1
  • β-amido EWG on both sides +2
    Score 4 - Category 4 (cannot be reached without calculating β-amido).
    Removed from HC list.



  • Alpha-hydrogen score 1
  • β-amido EWG +1
    Score 2 - Category 2 (cannot be reached without calculating β-amido).

The substituted β-amido effect remains an element in the limit list of all big regulators (HC, TGA and EMA - see example N-nitroso-desethyl-lidocaine, FDA - see example N-nitroso-safinamide) and integrated in CPCA (cf. Cross KP and Ponting DJ, 2021, Developing Structure-Activity Relationships for N-Nitrosamine Activity, Comput Toxicol, 20:100186, where they are referred to as “β-carbon electron withdrawing groups").

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Lidocaine metabolizes to 2,6-dimethylaniline (or 2,6-xylidine)
Identification of 2,6-xylidine as a major lidocaine metabolite in human liver slices
This metabolite is a weak metagen and carcinogen substance:
A weight of evidence assessment of the genotoxicity of 2,6-xylidine based on new and existing data
Moreover Lidocaine (as all the anesthetics) is used only for short-term treatment.
I wonder which sense may have a limit on an improbable N-nitroso-desethyl-lidocaine, based on a lifetime approach.


Less-than-lifetime approaches and continued evaluation of the AI-value impact of (de)activating features remains very welcome, but don’t explain the removal of the AI from the list. It is indeed an advantage that lidocaine metabolism is very well described.

The mutagenicity of 2,6-xylidine has been significantly derisked in A weight of evidence assessment of the genotoxicity of 2,6-xylidine based on new and existing data.
Metabolisation of lidocaine does not only involve 2,6-xylidine as a metabolite, but also monoethylglycinexylidide = desethyl-lidocaine, which is also a Ph. Eur. impurity (impurity D). Considering the high diversity in lidocaine products, from anesthetics for hospital use to a high diversity of OTC galenic forms, and desethyl-lidocaine being an known and intrinsically nitrosatable impurity, I do not find it improbable a product might exist that requires setting an acceptable intake (daily lifetime as point of departure of LTL AI design), as reflected in the limit list of EMA, HC and TGA, even if it is very likely that for many products this is not a likely nitrosamine as well. Recent stoichiometric studies show that nitrosation conversion and selectivity (C-nitration on aromatic ring vs. N-nitrosation, cf. structure of desethyl-lidocaine: C-nitration risk para of the amino-group of the 2,6-xylidine) might significantly differ liquid phase vs. solid phase. Though these studies are stoichiometric and under stirring/mechanical impact (possibly influencing extrapolability), general improbability of a synthesisable nitrosamine cannot be concluded when a high diversity of products exists. Many nitrosamines in the international limit lists cannot be formed selectively in stoichiometric liquid phase experiments but this does not per definition mean improbability of the impurity.
It is true that lidocaine EP impurity E has a double risk for C-nitration compared to lidocaine EP impurity D due to having two aromatic rings, but I deem the risk for mischaracterisation of the “nitrosamine” that was possibly reported reasonably low from a compound characterisation science perspective, making the scenario where the error lies in the redacting of the limit list more likely maybe (e.g. identified need based on step 2 submissions to list nitroso impurity D, but listing nitroso impurity E instead by reading the wrong line in the monograph).

When considering some elements of lidocaine/monoethylglycinexylidide metabolism extrapolatable to N-nitroso-monoethylglycinexylidide (N-nitroso-desethyl-lidocaine): I believe amidolysis metabolisation for beta-amido nitrosamines is intrinsically part of the design of the nitrosamine deactivating feature beta-amido (thus linking it with deactivating feature COOH: strong binding to plasma proteins and rapid excretion). The fact that the amine metabolite 2,6-xylidine is not highly potent supports the validity of this design (and often the theoretic amidolysis metabolite of the nitrosamine and the API will be the same), thus confirming that the nitrosamine and not the amine is the typical focus. (Comparable to how for nitrosamine metabolisation also the diazonium-ion related risk and not the formaldehyde risk is the focus based on potency ranking. For discussions of formaldehyde as an alpha-hydroxy-nitrosamine metabolite, including a discussion on the toxicity of formaldehyde: Peterson, L. A., Urban, A. M., Vu, C. C., Cummings, M. E., Brown, L. C., Warmka, J. K., Li, L., Wattenberg, E. V., Patel, Y., Stram, D. O., & Pegg, A. E. (2013). Role of Aldehydes in the Toxic and Mutagenic Effects of Nitrosamines. Chemical Research in Toxicology, 26(10), 1464–1473. https://doi.org/10.1021/tx400196j.)


Actually in some specific pharmaceutical forms and markets the use of Lidocaine could be considered as chronic (for some decades, not lifetime per se). It depends on the approved pathology for the particular drug product.

Thank you very much Yosukemino for your update and the highlights, much appreciated!!!
Do you have any comment on the limits of N-nittosopalbociclib and N-nitrosoribociclib? In EMA list also, the AI of N-nitrosoribociclib was set as 400ng/day. As it is also metnioned from other persons, this is not according to the guidelines, as the corresponding APIs are used as drugs for advanced cancer and their nitroso-impurities should be controlled under the ICH3B

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Thank you for sharing, much appreciation

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Amides are mildly electron withdrawing so I advice that you add that +1. This is the downside of CPCA. These are random numbers and based on handwaving assumptions. But I would say, consider the beta amido as an EWG in your evaluation. It is definitley not an electron donating or neutral group.

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