Please find below a synopsis of the questions that were discussed and answer during the session. Quite insightful session, congrats to AAPS for putting this together.
What in silico tools are available to aide in performing a nitrosamine risk assessment? In your experience how well do they work, how accurate are they?
In silico tools such as Mirabilis can be used for purge calculations. Work is also on-going to refine in silico SAR tools to examine mutagenicity / non mutagenicity within N-NOs. Actual modelling of reactivity e.g., Nitrite + Secondary amine can be modelled using Berkeley Madonna / Dynochem etc.
What are companies doing for Nitrosamine Risk Evaluation on Phase 1 formulations and for early formulations that intended for bioavailability evaluation only?
The current regulatory position regards the management of N-NOs remains somewhat unclear. As Nitrosamines are mutagenic impurities then ICH M7 should technically apply as ICH M7 applies to all clinical phases. However ICH M7expressly permits the use of durationally adjusted limits i.e.,. limits based on duration. The real issue is that the current stance regarding N-NOs is that durational adjusts are not permitted. It is very difficult to envisage how control of N-NOs could be achieved during phase I studies if lifetime limits are applied. The only guidance that currently specifically states the need for control during clinical phase is Health Canada guidance.
To add to Andy’s point, we do conduct evaluations in early Phases. For example, a few ways to help derisk a formulation in Phase 1 is to increase the pH of solutions/suspensions, source low-nitrite excipients, avoid excipients with low surface pH (such as dicalcium phosphate).
It seems that in some cases it is simply unavoidable to form an API-Nitrosamine. Are there other options than inhibitors?
The main issue is that secondary amines will react with traces of Nitrite under DP formulation conditions and although we can look to reduce Nitrite levels in common excipients we cannot reduce to zero and for a secondary amine levels will exceed limits such as 18ng. This therefore is an issue of appropriate safety limits for NDSRIs
Any insights on nitrosation efficiency of DMA in non-aqueous environments with low levels of nitrite? What about situations when an organic solvent is used with a strong acid (e.g., negative Hammet pH), when DMA is fully protonated? Can nitrosation occur to any relevant levels?
Thanks for this question to date most focus has been on aqueous models both for API and drug product. Critical to this is that for a reaction to occur you need a nitrosating agent. Nitrite requires water to yield nitrous acid. I’m uncertain how reaction could occur in a non-aqueous environment
What are the identified root causes for the presence of nitrosamines in products?
The initial primary root cause for the presence of nitrosamines in products was associated with the API. E.g., Valsartan The presence of nitrites in the drug formulation can also contribute to the formation of nitrosamines depending on the reactivity with the API. This is particularly true of secondary amine APIs. To the extent that where combined with extremely low limits i.e., 18ng/day this has now become the primary issue.
The reactivity of the vulnerable amine is key: low pKa secondary amines can be quite reactive, and even if present as minor impurities in the API, they can form nitrosamines at these threshold levels.
Acidic agents are not always compatible with APIs (Maillard reactions, polymorphic change…). Are other scavengers than Vit. C and Vit. E known and which can be used in pharmaceutical formulations? Maybe some that aren’t acidic?
Yes, there are a few options listed in this paper: Redirecting. Primary amines can interact with nitrites and form innocuous byproducts, however, the pKa of the vulnerable amine is key to understand how successfully another agent can outcompete it in interacting with the nitrosating agent (from nitrite).
In cases due to poor solubility of the API, one may be forced to spray dry from an ICH recommended spray dry solvent like DMF (DMSO is not as easy to dry vs. DMF, so DMF is still preferable). Any suggestions on how to derisk this as well, besides trying to ensure the DP microenvironment is has a pH >~5.5 to minimize kinetics of nitrosamine formation using DP components that are low nitrate?
There are several factors thst need to be considered these include
Nature of the API - is it a secondary amine, what is its pka
Also how much water is present - nitrite needs to convert to nitrous acid to form a nitrosamine
Finally avoid naked flames - seen with excips this can lead to NOx species
Have you also experienced that the biggest impact on nitrosamine is temperature even without humidity?
Higher temperatures will increase all reaction rates (include those of competing inhibition reactions); water is key to allow formation of nitrous acid (the nitrosating agent from nitrite). However the interplay of plasticization of excipients or API surfaces by water can be a dominant factor, and will be formulation/product specific. There are models available to help answer this question for specific situations.
Are products containing excipients potentially at risk of contamination with Nitrosamines?
With respect to excipients, the questions that should be considered are: can an excipient directly introduce a nitrosamine or a reactive amine that can convert to a nitrosamine within a drug product? Or are there excipients known to contain nitrosamines? An example of an excipient that is known to contain a nitrosamine as an impurity is trolamine (triethanolamine) and the nitrosamine impurity is N-nitrosodiethanolamine. In the European Pharmacopeia, the limit for N-nitrosodiethanolamine is established at 24 ppb. While this particular excipient may contain a nitrosamine impurity, in general, the risk of an excipient introducing a nitrosamine directly to a drug product is negligible. A more important consideration is whether or not an excipient has nitrites present. If so, is there a potential for the nitrite in the excipient to interact with the API to form a nitrosamine. The impact of nitrites in a given excipient should be evaluated individually for each drug product for any potential risk. Whether the presence of nitrites in an excipient is a significant risk factor will depend on the components in the drug product formulation. When modelled however in processes such as wet granulation, even nitrite levels <1ppm present a concern at limits for N-NOs of 18ng /day.
Nitrites in excipients are quite ubiquitous, and one should assume low levels will be present. Here’s a good reference (https://doi.org/10.1016/j.xphs.2022.04.016)
Are other nitrosating sources known - other than nitrites in the excipients?
Yes. Nitrosating agents can originate from the synthesis of the API. Levels of nitrites in excipients, and water, may be considered primary sources for introduction of nitrites in a drug formulation albeit at low levels. However, be mindful that there can be many sources of nitrosating agents. See the diagram below.
Who is responsible for putting together the nitrosamine risk assessments for an excipient (the supplier vs. the end user)?
As communicated in the IPEC Federation position paper on nitrosamines, the responsibility for overall risk assessment for the presence of nitrosamines in a drug product lies with the MAH or the drug product manufacturer, depending on the region. So, how should excipient manufacturers and/or suppliers support MAHs with their risk assessments? First, it should be made clear that excipient manufacturers are under no specific regulatory requirement to provide risk assessments on nitrosamines to regulatory agencies. However, it is in the interests of excipient manufacturers to provide information that would facilitate the safe use of their excipients generally, and equally for nitrosamines risk assessments. When levels of nitrites or vulnerable amine impurities are known to be present in an excipient, that information should be provided to the drug product manufacturer, drug product distributor, and/or MAH, by the excipient manufacturer or supplier. Collaborative discussions between the excipient manufacturer and the drug product manufacturer, drug product distributor, and/or MAH should occur when needed to ensure available excipient information is understood within its proper context. The ultimate goal is to ensure safe and effective medications are available for the treatment of diseases. Note also industry has developed a comprehensive data base relating to Nitrite levels in common excipients.
How should one execute a robust Nitrosamine Risk Assessment?
For the initial risk assessment associate with API - main issue is presence of a secondary / tertiary amines AND a nitrosating agent - As modelled by Ashworth et al water is not a significant issue when addressing a trace / trace scenario
For DP - then the risk primarily associated with seondary amines either the active itself or traces of secondary amine (e.g. diethylamine in triethylamine ) - and of course nitrite levels in excipients
All of these points are addressed in EFPIA API and DP decision trees
Finally, industry are developing predictive models - one already exists for API (Ashworth) - DP is under development.
For Phase 2a and Phase 3 formulations when is it recommended to do Nitrosamine Risk Assessment: (a) pre-PSB when locking the formulation in place or (2) pre-filing when probability is high that it will be a marketed product or (3) maybe there is a 3rd option
This is very difficult to give a simple answer to. Irrespective of the phase it is sensible to at least consider high risk factors such as if the active is a secondary amine. Other aspects such as the synthesis route should be considered, especially the general risk of presence of amines (secondary and tertiary) as well as obvious sources of Nitrosating agents are identified.
In your experience how successful have risk assessment been in allowing companies to avoid extensive testing for nitrosamines? Have agencies been accepting of this approach?
We have had some success based on modelling. N-NOs are in fact a widely studied class; albeit some 50yrs ago. We know and understand the various risk factors such as:
*Mechanism / rate constants
*Impact of concentration of reactants / pH / pka of the amine / temperate – time
Using this knowledge modelling of levels of formation in API has gained traction with authorities. A similar approach to DP is now being actively developed. Purge calculations, specifically for reactants, have also gained some acceptance.
Risk assessments that have rigor, with strong analytical data to back them up, have been generally successful.
If multiple nitrosamines are detected in a drug product, what is the acceptable limit?
There are evolving regulatory positions on this: some HAs expect that the sum of all nitrosamines (if more than 2 present) be controlled to the level of the nitrosamine with the lowest ADI (e.g, in a mixture of NDMA (ADI=96 ng/day) and NDEA (ADI = 26.5 ng), the mixture would be controlled to 26.5 ng/day). More recently, Health Canada adopted a different approach, which Andy can comment.
Recently both EMA and Health Canada has issued revised proposals. Where the risk of multiple N-Nitrosamines is <10% of one of the N-NOs AIs then there is no need to specify it. Similarly if >10% then risk can be calculated based on 1 in 100,000 risk as opposed to controlling both to the lowest AI