Nitroso-Sitagliptin Who/Where/Limit?

A community member brought it to my attention and ask to share it.

  • EMA and Health Canada have issued an update on viz Nitroso-Sitagliptin (7-Nitroso-3-(trifluoromethyl)-5,6,7,8-tetrahydro [1,2,4] triazolo- [4,3- a] pyrazine).
  • The impurities have been found in both API and finished dosage form (DP)
  • EMA has defined a maximum exposure limit of 37ng/day
  • The nitroso-impurity appears in both as a process impurity in the API and in the drug product, which seems to increase over time during storage


viz Nitroso-Sitagliptin

What do we know ?


As per Route of synthesis pyraizine HCl used as KSM/Intermediate and structure of pyraizine HCl and nitroso sitagliptin almost simillar.

I have not find out respective documents in EMA and Canada site, can you please share the documents.

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Please find the limit in the recent update from EMA

Q_A_for_marketing_authorisation_holders_1656674375.pdf (842.3 KB)


@Naiffer_Host Thank you very much for the updated guidance.

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@schlinjo1975 as reference to our discussion this morning…

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Thank you very much for providing guidance.

Interestingly, Health Canada has also aligned the limit for this impurity to 37 ng/day based on a read-across approach with 1,2,3,6-Tetrahydro-1-nitrosopyridine.
An AI limit of 153 ng/day was earlier tentatively accepted by HC and some EU authorities based on a read-across using 1,2,6-Trimethyl–4-nitrosopiperazine as a surrogate.

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Hi, @Muzaffar.
Thank you for sharing the information. It’s interesting!! I understand the tentative limit of 153ng/day for Nitroso-Sitagliptin(NTTP) assigned from 1,2,6-Trimethyl–4-nitrosopiperazine was replaced with 37ng/day from 1,2,3,6-Tetrahydro-1-nitrosopyridine(NTHP). And NTHP was also used for the calculation of the Nitrosovarenicline(NNV) limit. As @kpcross explained in the varenicline topic, analogs that have similar reactivity of the nitrosamine functionality are important.



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Hello @Yosukemino,
Thanks for you inputs. Yes I agree with you.
Along with the toxicodynamics, it is also important to review the physico-chemical properties (Log P, pKa etc.) of the impurity and the surrogate as it would eventually impact the toxicokinetics i.e. absorbtion, distribution, metabolism and excretion (ADME) properties.
In the case of Nitroso-Sitagliptin, I believe NTHP is a better surrogate when compared to 1,2,6-Trimethyl–4-nitrosopiperazine while considering this aspect too.

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Dear Naiffer, do you have any link that could be shared about this topic? I am surprised to see that the nitrosamine impurity increases upon storage of the API.
Thank you, regards


@Dan I do not have specific reference to the formation mechanism of the impurity reported by EMA in their recent update; however, it has been documented the formation of a species: 3-(trifluoromethyl)-5,6,7,8-tetrahydro [1,2,4]triazolo[4,3- a ]pyrazine as degradant during stability testing which might be reactive with nitrosating agents present in the formulation.


Perhaps @MichaelBurns or @fernandaw can help us with the structure or species identification

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Thak you @Naiffer_Host .
I’m aware of the risk associated to excipients with respect to nitrosation (e.g. []). I was particularly intrested in how the specific nitrosamine reported by EMA could increase in the API upon storage, but probably I misunderstood the post :thinking:. Thanks again!

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Dear @Naiffer_Host,

FDA is now considering an interim AI of 246.7 ng/day for NTTP.

Do you have any idea how this limit was arrived and which surrogate was considered for arriving at this limit?

"Although there are no data available to directly evaluate the carcinogenic potential of NTTP, FDA used information available on closely related nitrosamine compounds to calculate lifetime exposure limits for NTTP.

Agency scientists evaluated the risk of exposure to NTTP at interim acceptable intake levels up to 246.7 ng per day and determined that it presents minimal additional cancer risk when compared to a lifetime of exposure to NTTP at the 37 ng per day level."


What is interim acceptable limit and how long it will be valid. Any clarification for the term interim limit. It certainly create doubt amongst pharma industry for method development and testing finished product.
Also in drug product specification , can I go with interim limit in my dossier submission.


@sameer while FDA has not provided general guidance on these terms, may I suggest looking at the post made by @Yosukemino with the recent update from EMA on these concepts and general guidance.

Temporary Limit:
To protect public health, to inform decisions on required market actions while ensuring at the same time availability of medicines while a formal AI is established, a temporary AI (t-AI) of 178 ng/day (total nitrosamines) can be adopted by the relevant authorities for marketed medicines identified to contain one or more nitrosamines exceeding the TTC of 18ng/day. This t-AI has been derived using TD50 values calculated in the Lhasa carcinogenic potency database and is based on a probabilistic approach that there is a 33% risk that the “true” AI is below the t-AI. It is expected that the t-AI would be used for a period of less than 12 months.

Analytical Target:
The t-AI should not be used as a target for development of validated analytical methods to quantify new nitrosamines since the long-term limits adopted by CHMP might ultimately be lower than the t-AI

@Naiffer_Host . Thanks for sharing so quickly. It is extremely helpful.

New development…

Yesterday, it was reported that the source of contamination was identified, and plans to fix the issue is underway.

While it wasn’t clear whether Merck or a third-party manufacturer was responsible for the contamination, the agency temporarily allowed sales of the drug to continue even though some samples exceeded the 37 nanogram (ng) threshold for daily intake.

The FDA’s decision also was influenced by a shortage of the injected blood-sugar-reducing drug, which if discontinued by a patient can have dangerous consequences.

“(Merck) has already instituted additional quality controls and expects to be able to consistently reduce NTTP levels to meet the long-term acceptable daily intake level this year,” the company said in a statement to Fierce Pharma. “The specific timeframe will be based on the progress of timing to institute process modifications and on engagement with FDA and other health authorities.”

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It would be interesting to see regulatory agencies publishing details for pharma industry to mitigate risk in their product

Dear Naiffer,

As far as I understand, EMA’s 178 ng/day t-AI limit would not apply in the case of NTTP impurity since an official AI has already been established at 37 ng/day. And considering the long-term indication of sitagliptin, neither would the Q22 limit…


Is anybody aware of the analytical method already available? Is that something we should get donate to our analytical hub?