Nitrosamines in small molecule API development
27th Aug 2024
Sparked by a series of recalls and regulatory initiatives over the last several years, there is an intense focus on eliminating and mitigating nitrosamines in active pharmaceutical ingredient (API) development and manufacturing. Classified as known or probable carcinogens, these impurities must be kept below an acceptable limit in drug products if they cannot be avoided altogether.
The 2018 recall of blood pressure medication valsartan due to the nitrosamine NDMA triggered a long line of additional product recalls, heightened regulatory scrutiny, and increased public concern. Since then, there have been more than 250 nitrosamine-related drug recalls , and regulators have been intently focused on preventing these carcinogens from entering drug products. For pharmaceutical and biotechnology organisations, the quest to eliminate nitrosamines entails rigorous testing, careful raw material selection, process changes, and more.
Read on for more information on the causes and potential risks of nitrosamines, the efforts regulators have taken to combat them, and how pharmaceutical organisations can effectively limit these impurities early in development to produce safe, high-quality products.
How nitrosamines form
An understanding of how nitrosamines surface is imperative to limiting or eliminating them. Nitrosamines typically form when nitrite reacts with a secondary or tertiary amine under certain conditions. They can surface in a variety of ways and at various stages of API development, whether from starting materials, reactions that occur during manufacturing, or other sources. It is estimated that 20% of small molecule drugs contain what are considered to be vulnerable amines, which are precursors for nitrosamine formation.
Sometimes, nitrosamines can be circumvented in development by carefully selecting raw materials and avoiding nitrosating agents. For products that are already susceptible to nitrosamine formation, these impurities may be more likely to form under certain storage conditions. This makes accelerated stability studies before validation and post-marketing surveillance, once a product goes commercial, critical. This allows scientists to set stringent storage requirements to prevent nitrosamine formation and ensure product safety.
A look at the regulatory landscape
Since challenges with nitrosamine were first identified in 2018, regulators around the world have released guidelines to address nitrosamine formation and prevent them from forming in novel APIs and drug products. These regulations identify acceptable daily intake limits for nitrosamines based on their carcinogenic risk—for example, the World Health Organisation, European Medicines Agency, and US Food & Drug Administration limit N-nitrosodimethylamine (NMDA) intake to 96 ng/day, but limit nitrosamines like N-nitrosodiethylamine (NDEA) N-nitrosodiisopropylamine (NDIPA) to just 26.5 ng/day.
In addition to specifying limits for nitrosamines, regulators have also released guidance around detection and prevention. In 2020, the US FDA released its guidance ‘Control of Nitrosamine Impurities in Human Drugs’ , which provides recommendations around nitrosamine testing approaches, process design, and other measures to avoid mutagenic impurity formation. The International Council for Harmonisation (ICH) last updated their ‘Guideline on assessment and control of DNA reactive (mutagenic) impurities in pharmaceuticals to limit potential carcinogenic risk’ in September 2023. In addition to establishing a Nitrosamine Implementation Oversight Group, the European Medicines Agency has released guidance with detailed instructions around risk assessments and testing protocols.
While regulations around nitrosamines are updated frequently and vary in different regions of the world, they all share a strong emphasis on appropriate risk assessment, sensitive analytical methods, process controls, and detailed documentation. Analytical methods are generally dictated by the identity of the nitrosamine being formed, but since nitrosamines can be hazardous in very low concentrations, techniques like gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) are often preferred for their high levels of sensitivity and selectivity.
Strategies for limiting nitrosamines
Regulations only mandate nitrosamine risk assessments prior to commercialisation, but the earlier potential nitrosamines can be identified and mitigated, the better. When nitrosamine risk assessments are performed early in the process, scientists can more proactively develop appropriate analytical methods or explore alternative routes that mitigate or avoid nitrosamines altogether. As organisations get deeper into the development and manufacturing process, it becomes much more challenging, time-consuming, and costly to control nitrosamines. Let’s explore some strategies for nitrosamine elimination at various stages of development and examine how they impact the process.
One important way to avoid nitrosamines is at the raw material level, ensuring that all materials are tested for potential nitrosamines and avoid recovered solvents, catalysts, and reagents. This allows project teams to avoid introducing carcinogens from the start, and in turn, may help to prevent them from having to alter processes down the line. Working with trusted vendors and maintaining awareness across the supply chain can help organisations to maintain confidence in the quality of the materials they use.
If nitrosamines are expected and the process is in early development, there are several measures scientists can take. Scientists should first examine the reagents involved, looking for suitable alternatives to nitrosating agents and secondary or tertiary amine reagents wherever possible. For example, lithium diisopropylamide may be replaced with potassium t-butoxide. Similar to selecting alternative raw materials, this is one of the most straightforward ways to eliminate nitrosamines without significantly impacting the process.
If these materials cannot be avoided, scientists may look to separate sensitive functional groups, i.e. secondary and tertiary amines, from steps that involve nitrosating reagents, oxidation, or nitric acid. This may include setting targeted reaction conditions that avoid n-nitrosation, or minimising the amount of oxygen, which can form radicals that generate nitrosamines.
Finally, if the process does not allow scientists to avoid potential nitrosamine formation altogether, they may look to adjust the process and move the nitrosamine-forming step earlier. This may allow scientists to frame the process in such a way that any nitrosamines formed early on would not persist in downstream steps, or enable scientists to more easily detect and remove them later in production.
After a product has already been validated or reached the market, it becomes much more challenging and costly to alter the process and mitigate potential nitrosamines. Any significant changes to a process must be re-validated and then re-submitted for regulatory approval. In this case, scientists may aim to remediate potential nitrosamines as part of final product isolation, as opposed to reworking earlier parts of the process, to help lessen the time, cost, and regulatory impacts of post-validation changes.
A comprehensive approach to mitigating nitrosamines
Effectively addressing nitrosamines requires a deep understanding of how and when impurities form, expertise in sensitive analytical methods that can detect nitrosamines at low concentrations, and a thorough framework that is aligned with the latest regulatory guidelines. An experienced partner can account for all of these considerations efficiently and collaboratively.
Our approach to nitrosamine testing and mitigation at Sterling is proven and thorough. Robust controls are in place to eliminate nitrosamine related risks due to general causes such as process water quality or cross-contamination between products. For each individual product, as part of our standard operating procedures, we begin with a questionnaire form that is regularly updated to align with the latest literature and industry regulatory guidance. Starting in early development, we examine the process from every angle to evaluate the risk of nitrosamine formation, and we leverage extensive expertise in analytical chemistry to identify and quantify impurities. By evaluating nitrosamines and shaping strategies to mitigate them early on, we help our customers develop safe and high-quality products while containing costs and project timelines.
If you’re interested in learning more about our approach to nitrosamine testing and other impurities, contact an expert team member or visit our Knowledge Hub for more insights.
