Are nitrosamines the connecting link or one of the connecting links between the concepts of phototoxicity and photocarcinogenicity due to the intake of a contaminated medication according to the 2019/ 2023 FDA list?

Nobody has also shared the opinion till now that most of the photosensitizing drugs worldwide, are recently indexed in the fda list from 2023 as potentially contaminated:

The link between phototoxicity / photocarcinogenicity skin cancer development and porgression could be linked to a significant extend to the intake of exactly those potentially/ really contaminated drugs?

Could we check this ?

Any proposals?

the contamination of the multimedication within the nitrosamine era and in the last 40 years when we look back- is this a possible simple explanation regarding the rising skin but also other type of cancer incidence world wide?

Any idea?
Data on that topic are limited worldwide, but now we have probably to start to look at that direction?

Complete elimination regimes for nitrosamines and NDSRIS?

For APIs which were shown to be photosensitizers and have an investigated link with skin cancer, such investigations should not per definition be broadened to their NDSRIs I believe, as not all α-hydroxy NDSRIs are in fact mutagenic metabolites, whereas the photo-based route to nitrosamine mutagenicity has (based on limited cyclic nitrosamine examples) been identified as another way to the same effect: replacing CYP-enzyme mediated α-hydroxylation (indirect mutagenicity mechanism) by photo-mediated α-hydroxylation (which to be a direct mutagenicity mechanism also requires that further metabolization of the α-hydroxynitrosamine to the diazohydroxy metabolite and the diazonium ion is downhill in energy, which is for non-cyclic nitrosamines not per definition the case, whereasα-hydroxynitrosamine detoxification might be).

All risk management systems for nitrosamines organized by regulators I have seen over the years are based on the assumption that an α-hydroxylation mechanism of metabolic activation is responsible for the mutagenic and highly potent carcinogenic response observed for many N-nitrosamines. Recent literature published mechanistic reviews have reconfirmed this to be a valuable assumption. Not only is it evaluated if the nitrosamine can chemically α-hydroxylate (availability of α-carbon hydrogens), it is also evaluated how relevant that mechanism is compared to other metabolization mechanisms and how relevant it is that an α-hydroxy nitrosamine is responsible for a mutagenic response in the end based on structure and further metabolization potential. Doesn’t this umbrella cover the irradiation based activation, as they are α-hydroxy nitrosamine based per available data?

In nitrosamine mutagenicity risk assessment it is not only studied if an α-hydroxylated nitrosamine can be formed upon metabolization, but also if that would be a mutagen and if so how potent.
If that α-hydroxylated nitrosamine can cause mutagenicity, the nitrosamine will typically be controlled to protect the patient in a way striving for a lifetime cancer risk of 1 in 100000 and consider risk/benefit elements.
This is protecting the human population to an increased risk of cancer to 1 in 100000, when the actual incidence of cancer is unfortunately 1 in 2 for all cancers (NHS 2023) or 1 in 58 for UK males and 1 in 122 for UK females for liver cancer (CRUK 2023) with comparable incidence globally (data review Dr. George Johnson).

If a nitrosamine subjected to α-hydroxylation via CYP enzymes does not generate mutagenic species and is for example Enhanced Ames test (maximizing metabolic activation and developed by regulators, including consideration for available literature Ames studies – cf. available irradiation-based studies) negative, it does not seem critical to me to confirm the same with the use of irradiation instead of enzymes (as another means to the same end), especially considering the complexity of the structure of NDSRIs and the risk for alternative observations. If that were to be done, the non-nitrosated version of the NDSRI can be considered as a control.

For an Enhanced Ames test positive nitrosamine reconfirmation of said positivity with an irradiation-based Ames test could be considered to increase the understanding of the mechanistic balance, but what more information will it give towards a control? And can’t we assume that in follow-up or historic animal studies light exposure is included?

Of note, the FDA NDSRI list is hypothetical, as also indicated by the Agency in the list and cannot be seen as a direct confirmation of the presence of NDSRIs in drugs with photo-sensitizing APIs.


ok, I agree, but it seems that some nitrosamines could be carcinogenic/ photo carcinogenic without metabolic activation:
Mutat Res Genet Toxicol Environ Mutagen

. 2024 Jan:893:503721.

doi: 10.1016/j.mrgentox.2023.503721. Epub 2023 Dec 2.

Genotoxicity and the stability of N-nitrosomorpholine activity following UVA irradiation

Haruna Mochizuki 1, Yukari Nagazawa 1, Sakae Arimoto-Kobayashi 2

Affiliations expand


This study investigated N-nitrosomorpholine (NMOR) genotoxicity following UVA irradiation without metabolic activation. Following UVA irradiation, the photo treated NMOR (irradiated NMOR) was directly mutagenic, without UVA or metabolic activation, in the Ames test. The activity was relatively stable, and approximately 79% of the activity remained after 10 days of storage at 37 °C, 4 °C, or -20 °C. Micronuclei (MN) formation was observed in HaCaT cells after treatment with irradiated NMOR without metabolic activation. The action spectrum of MN formation in response to NMOR irradiation followed the NMOR absorption curve. In vivo, MN formation was observed in the peripheral blood reticulocytes of mice injected with irradiated NMOR under the inhibition of cytochrome P450-mediated metabolism of NMOR. Volatile NMOR may attach to environmental materials and be irradiated with environmental UVA light. Photoactivated NMOR-attached air pollutants could float in the air and fall onto the human body, leading to genotoxicity induced by the irradiated NMOR.

Keywords: Mammalian cell micronucleus test; Mammalian erythrocyte micronucleus test; N-nitrosamine; Photogenotoxicity; Photomutagenicity.

Copyright © 2023 Elsevier B.V. All rights reserved.

How we can control this ?

Are there already data aboyt all nitrosamines / NDSRIS and their procarcinogenic / phototoxic effects without metabolic activation?

wouldn’t it make sense to conduct tests to clarify this

the idea is the following one if the community would like to have this in mind: combined intake of potentially contaminated drugs, officalised in the FDA lists COULD have possible photocarcionogenic effect regarding the development of skin cancer. The severeity of the clinical picture often corresponds to the parallel intake of more probably/ really contaminated drugs! The overlapping of the pathogenetic genes for skin cancer- p53 and RAS oncogenes as a whole and the gene defects caused by nitriosamines or tobacco specific nitroamines - also p53 and RAS oncogenes , are at least indicative that photocarcinogenic affects of the nitrosamines regarding skin cancer, are not only a myth…

Are we not controlling this then by applying very low limits for NMOR in medicines, intrinsically applying a precautionary principle for the protection of human health and considering already that NMOR can introduce tumors?

Where scientific uncertainty would exist, this is surely compensated by low limits and other protective elements applied in international guidance.

I believe my original answer addresses this already.
What phototreatment was proven to do is generate the alpha-hydroxy nitrosamine from the nitrosamine (as usual such metabolites can be O-conjugated). The alpha-hydroxy nitrosamine metabolite is exactly what the focus is of the call for review. Replacing metabolic activation with photoactivation to get the same type of metabolite of concern doesn’t make the metabolite itself different in potency and where the enzyme-mediated activation is considered very likely in a mutagenicity risk assessment like in the case of NMOR an alternative way to the same type of risk doesn’t change the mutagenicity risk assessment for the type of exposure that is the focus of nitrosamine contamination in medicines? Though I understand you want to link the activation subtype to the tumor site of interest and the subtype of cancer pathogenesis at risk (while also linking with specific gene mutations causable by certain nitrosamine metabolisations and linked with skin cancer), I don’t see concerns being raised in literature on the currently applied MoE linked to diversification of (understanding of) pathogenesis scenarios?

Note that over the years research has also been done on the relevance of using liver enzymes in the Ames test where for a certain group of mutagens (including nitrosamines) liver was not the most relevant tumor site, allowing investigations to diversify where needed, supported by specificity investigations on the Ames test for nitrosamines. The fact that we still use liver enzymes predominantly indicates that it is the activation effect that matters, not if it would be the exact same catalyst casing that activation in vivo (even when it would be non-enzymatic).

The anticipated metabolism of the N-nitrosamine (and the cytochrome P450 enzymes most likely involved) is surely considered when mutagenicity testing on nitrosamines is designed.

It is not so exceptional to test also mutagenicity of metabolites instead of mutagenicity of the impurity or to design mutagenicity testing around alternative activation mechanisms (though the in vivo balance between toxification and detoxification has to be considered), but considering the available (in vivo) data on NMOR that was used for acceptable daily intake development and the principle of a very low LCR for extrapolating data, I don’t see something that is missed at the moment or an indication that the degree of nitrosamine alpha-hydroxylation activation that can be reached in vivo based on enzymes is much lower than based on photo-effects and also missed fully in in vivo studies and not governed in the conservative approaches to AI setting?

That perspective could have been different of course if totally different/new metabolites of concern are seen upon applying alternative activation introducers, depending on the in vivo relevance of such activations. For example if an NDSRI would be EAT negative with and without S9, the API Ames test negative upon photo-activation without S9 and the NDSRI Ames test positive upon photo-activation, whereas in vitro irradation of NDSRI gives showable new metabolites with a nitroso metabolisation link. (NPIP, NMOR, NPYR don’t match that trend.)

Generally, enzyme use in testing also serves detoxification and direct and indirect mutagenicity are assessed together for new nitrosamines. Insights in cytochrome P450 enzyme binding of nitrosamines can be helpful. For non-environmental exposure scenarios, the irradiation effect if any will never be naked from the enzyme effects or overall ADME (and enzymatic/non-enzymatic NDSRI detoxification potential)?

An integrated exposure risk assessment for nitrosamines would not only be focusing on the intake of multiple medicines, but also on diet, air, soil,… and is not evident to achieve. At the same time full integration requires in depth insights on in vivo nitrosation and in vivo detoxification balances. Note that limits for nitrosamines in medicines are typically much tighter than regulated for food or tobacco products.

An increase is carcinogenesis understanding is always welcome, but from this particular research I don’t see a significant diversification compared to existing considerations in medicines risk assessment or causal proof for the link between skin cancer incidence and the intake of specific nitrosamines via specific medicines?

The guidance for mutagenicity risk assessment for nitrosamines took quite some research to develop and publish and seems at a point where it is reflecting a industry and regulators agreement of what is a conservative way to protect human health, considering that nitrosamine cancer risk are indeed not a myth, but structure dependent.


I will
Respond to
Each statement of you, however a lot of thanks clarifying also some positions of you!
Regarding the first statement:
The most or the best protection is the elimination!
It has been already shown that specific groups of patients taking Sartans in specific geographic regions like Turkey , could have completely nitrosamine free production! That means that impurities could be controlled and eliminated - let’s follow this production cycles ! Hope that u will

Here the paper I suppose:

I am
Not completely sure if the metabolic activation and the photoactivation are the same!
And at the end we have the same
Metabolites which are carcinogenic or photo carcinogenic ?
This has to be probably clarified ?!

Actually there is a link established already between the intake of nitrosamine contaminated drugs and melankma and / or scc / bcc!
However the producers doesn’t officialise the types of nitroamines / ndsris which seems to be available in the drug!
Also we do not have any information about the possible metabolic/ photo- activation of certain procarconogenic substances in the drugs, which are presented already !
As u have mentioned - in very low concentrations ! However it has been found that only in one tablet of
Metformin- we could
Have 5 times more elevated concentrations and 30
Times more elevated concentrations only during the metformin intake
We have such a patients !

Here the paper:

We will
Officialise very soon patients that are taking metformin together with several new drugs, also listed in the fda potentially contaminated list , developing shortly till 16 cancers/ skin cancers!

From that point of view I don’t really see a lot of progress in the elimination of this carcinogenic substances which till the present moment are available in the drugs, but not officialised as incredients !!!
Medication contains carcinogenic substances and this substances has to be officialised ! Reason for that: that have serious influence of the incidence of skin cancer but probably not only!!’

Literature data connect exactly the intake
Of nitrosamine contaminated drugs with the specific skin cancer type!
The new wave on that point is called Nitrosogenesis of skin cancer / oncopharmacogenesis of skin cancer-

Here some data about that- it deserves attention:

Possibly it is useful to consider bigger datasets when trying to identify trends and causal relations, considering the baseline incidence of cancer and the multitude of contributing factors, e.g. (in case there is a mutagenic nitrosamine metabolite truly linkable to the API/medicine, thus requiring the significant presence in the medicine (and intake) of a related nitrosamine and its established mutagenic potential). You might find this a useful approach to avoid cognitive bias:
you_2023_oi_230968_1694461256.53093.pdf (
( Ranitidine Use and Incident Cancer in a Multinational Cohort - PMC (

1 Like

Thanks once again for the answer - I am working at the moment but will send several additional suggestions to be reviewed and probably discussed !

Interesting for me is the end product of the nitrosamines - the carcinogenic one after metabolic activation and the other one- that results from the photo toxicity/ without activation : dThe current state of knowledge: is it form both actions one and the same or it differs for the different nitrosamines and ndsris? These are two ways of activation of the carcinogenesis …

I completely agree and am very thankful for ur kind responces ! I will try to send several sporadic thoughts about this! These are data in reputable journals and I couldn’t ignore it! However I will try to give my explanation about that-
There are geographic areas where this contamination is avoided or could be seen as minimal so that that could be really big differences when we compare some data for
Africa , Soth America , Russia , India, etc- there are some
Areas where the data about this dramatic contamination are completely lacking or even not thematized! Data from that regions have been also not officialised even!
Eastern Europe is a similar place where this controlling mechanisms/ contamination officialization might be surely better than now! I see daily 2-3 patients with skin cancer and a huge % of them after intake of potentially contaminated drugs / regarding the official fda list ! For tha leat 8 years the % is more than 96!
Timely dependent dose internals and policontamination seems to be here a huge problem but an objective truth at the sam time ! We have surely a lot of work in front of us…
Thanks once again for the time invested to answer me…
We are living in the era of Nitrosogenesis and the rising skin cancer incidence , but surely not only skin cance- take a look at globocan prognosis for cancer incidence for the next 20 years!!
It’s a catastrophic one …

lot of thanks first again for the comments !:slight_smile:
I would
Like also to mention that not all mutagens cause cancer , some
Mutagens do
Not react in Ames test and are strong human carcinogens !

This is also a great debate …
Carcinogenic aganinst mutagenic action of nitrosamines !
The most test which has been used are not 100 % adequate for humans , because thay use bacteria as a substrate!!!
There is not complete reciprocity between significance of test using procaryotw organism !!
Human beings are not procaryotes !!
From here we have a great discrepancy between test significance for
Mutagenicity in bacteria and their equivalents in humans !!!

Complete eliminations of nitroamines in drugs must be the rule! Elimination standards and not tolerance ! Reason for that could be seen in the simualtenosly application of different carcinogenic / mutagenic substances like the ndsris and nitrosamines over relative short terms , leading to cancer development and
Cancer development is a multi step process which need different steps in order to became
Phenotypic or clinically distinguishable !!
Long term contact with ndsris in 6-7 different medications could lead to cancer development !
Please, take a look on our clinico- pathological correlations in papers in pubmed !

Another good paper showing that the metabolic activation of some tobacco specific nitrosamines is turning them to real mutagens / possible carcinogens:

Why we have to believe that the nitrosamines in drugs have a different action / some of them for sure yes…/ in comparison to that used in the study , I don’t know?

Mutagenic, clastogenic , carcinogenic action of nitrosamines seems to be a complex
Process , related to cancer development and progression….

The complexity could be shown on experimental and clinic pathological levels as it is happening now…

Important paper about our sensitive topic: