NDEA AI Limit 26.5ng/day?

Limits of Nitrosamines
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Hi, @Nilesh. I understand what you mean. And I’m sorry I’m not a toxicological chemist. The following post is similar to your question. It may derive from the reliability. And I recommend you to ask the same question to renowned toxicological experts including kpcross and David. They will kindly answer your question.

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Hi Yosuke,

I dropped my msg to them… lets see…

Moreover, I want to know about Lhasa TD50 & Gold TD50 difference… why we are considering Gold TD 50 instead of Lhasa TD50?

As per published guidance EMA & Health Canada, whatever AI limit has been derived for all published Nitrosamine impurity, which one is considered either Lhasa or Gold TD50?

Hope, I communicated question properly…

Thanks
Nilesh

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Moreover, what is the current practice is going on & all Regulatory agency which one is preferring?

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Ya… I know you are not Toxicologist…
You can answer, if you know, otherwise no issue

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I think the following video may solve your question. It includes how AIs were calculated.

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A few thoughts on these discussions:

  • The TD50s used for limit setting are typically the rodent TD50s, firstly since that is the standardised carcinogenicity assay (thus that exceptionally potent primate result for NDEA is ignored from the dataset), and secondly since rodent TD50s were used for the TTC and CoC initial development by Kroes, Cheeseman and co-workers. Additionally, a primate assay is less likely to be lifetime, due to longer lifespans, would use fewer animals for cost and ethics reasons, and is thus more typically used for mechanistic exploration rather than performed to make a formal determination of potency. In this case all non-rodent results seem to come from a single study looking at organ- and species- specificity in carcinogenesis (Adamson 1982).

  • Lhasa TD50s, for all that, as a Lhasa employee, I would argue are better, are based ultimately on the same data that the Gold TD50s were based on. The Lhasa TD50 calculation requires a certain threshold of data, such as having multiple dose groups, so there are many compounds (e.g. single-dose studies) for which no Lhasa TD50 exists; however, where both exist the values are typically very close (Thresher et al 2019 - we were aiming to replicate the original work of the Gold TD50s published in Peto et al 1984 but could not do so exactly), so it appears that the following process has been used:
    - determine whether a Lhasa TD50 exists for the compound/study, and use that as an initial ‘quality gate’ for the carc data.
    - there’s a caveat in this: For some reliable studies, such as the Peto et al 1991, we were unable to replicate the ‘lifetable’ method used by Gold, so there is no Lhasa TD50 currently published for this extremely-reliable study - we can calculate one, but it would be comparing apples with oranges, so the simple presence/absence of a Lhasa TD50 is not a complete quality gate.
    - use the Gold TD50 for that compound/study, for consistency with e.g. the TTC and CoC data.

  • There is a final subtlety, which is that the summary harmonic mean TD50s such as 26.5 ug/kg/day for NDEA are not the TD50s from a single most reliable study; a case could be made for the use of the TD50 derived from the 4000-rat Peto et al 1991 study, which would lead to 49.8 ug/kg/day (most sensitive organ/sex/species in most reliable study, as per M7). As I’ve mentioned in a couple of presentations ‘it’s hard to argue with 4000 rats’! The harmonic mean is a conservative way of determining a mean, and thus can be swayed lower by a single, lower-reliability, study that has an overestimation of potency w.r.t. the robust study.

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Hi, @David. Thank you for sharing your thoughts. I understand which TD50 is used for AI calculation.

  • Rodent TD50 is acceptable for AI calculation.
  • Lhasa TD50 is based on the same data on which GOLD TD50 is based. And GOLD TD50 is generally used for AI calculation, for consistency with the TTC and CoC data.
  • The harmonic mean TD50 is not the same as TD50 mentioned in ICH M7. The harmonic mean is conservative and can be swayed lower.

On the other hand, we know other nitrosamines (NMPA, NMOR, N-nitroso-1,2,3,6-tetrahydropyridine, NMPEA) do not use harmonic mean TD50s for calculation. Are NDMA and NDEA exceptions?

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I invited @Naiffer_Host to share this topic.

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Hi, @Naiffer_Host.
Thank you for sharing this topic.

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Thanks to David to nice explanation & Yosuke, who conclude very well.

Moreover, I didn’t see harmonic TD 50 value in below screenshot, what is it exactly & where it is?

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Dear David,
Kindly provide your technical input to Yosuke’s last line question.

Thanks
Nilesh

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The values circled with the light blue line are all harmonic mean. And TD50s on each study is in the Study Details and Citations.

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@Nilesh, are you referring to why NDEA and NDMA have limits derived from the harmonic mean as opposed to the study-specific?

I’m afraid I don’t know the answer to this, you’d have to ask the relevant regulatory agencies.

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I believe the report below will help. This is an extract from: EMA Assessment report Referral under Article 31 of Directive 2001/83/EC angiotensin-II-receptor antagonists (sartans) containing a tetrazole group Procedure no: EMEA/H/A-31/1471 (14-Feb-2019)

NDEA, like NDMA, is also classified by IARC as “probably carcinogenic to humans”.
Several TD50 values for NDEA are listed in the CPDB for rat, cynomolgus monkey and bush babies. The lowest calculated TD50 is 0.00725 mg/kg/day for liver tumours in the cynomolgus monkey. The TD50 for NDEA obtained in the rat is 0.0265 mg/kg/day. In rat besides liver tumours also other tumours were reported e.g. oesophagus, kidney, and vasculature in male rat. The extrapolation to the excess risk level for cancer is then done the same way as for NDMA by linear back extrapolation to the dose theoretically causing a 1:100,000 risk by dividing the TD50 by 50.000 (50% or 0.5 x 100,000). For NDEA this translates into a dose of 0.144 ng/kg/day extrapolated from cynomolgus monkeys and 0.53 ng/kg/day extrapolated from rat. For a person with a bodyweight of 50 kg this would result in an AI level of 7.2 ng/day (50 x 0.144 ng) or 26.5 ng/day (50 x 0.53 ng). 7.2 ng is equal to 0.0225 ppm and 26.5 ng is equal to 0.083 ppm in a 320 mg valsartan tablet. The difference between TD50 values based on different studies/calculations is considered significant. For the NDEA risk assessment it is therefore considered necessary to first assess the most appropriate TD50 to be used as a starting point.

angiotensin-ii-receptor-antagonists-sartans-article-31-referral-chmp-assessment-report_en.pdf (531.3 KB)

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That’s fine David…
Thanks for reply

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Thanks Naiffer sir, for your technical input & sharing the guidance…
Moreover, David also explained regarding the NDEA TD50 value…

Once again thanks to Naffier Sir, David & Yosuke…

At last, actually i am new to this Nitrosamine discussion.
As per my understanding, I am trying to connect the dots, understand the guidance… but still some query comes to my mind, which I want to resolve & understand and to know more about the Nitrosamine…

You can correct me, if my question/query is not up to the mark or irrelevant…

Your suggestion always welcome for me…

Thanks
Nilesh

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Thank you for your response, @David, and @Naiffer_Host. I remember agencies originally decided on the limit of NDMA and NDEA as interim limits. Those values may be calculated differently from the others.

Anyway, these discussions are very useful and informative!!

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