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Nitrosamine Impurities – Understanding Risks, Overcoming Challenges

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Nitrosamine impurities became a topic of focus when health regulators recalled valsartan, an antihypertensive drug, due to the presence of N-nitrosodimethylamine (NDMA), a probable carcinogenic agent and key member of the nitrosamine class.

Ever since the “sartan saga”, several batches of medicines contaminated with nitrosamines came to be known. The proportion of nitrosamines in these drugs does not pose a significant risk; in fact, small quantities of nitrosamines are found in foods and water, and most people are
exposed to them daily in minute quantities. However, the recall of commonly used drugs caused disruptions for patients across the globe. 

This article covers the basics of nitrosamines, their related health concerns and key steps taken by health authorities to prevent such product recalls in the future.

What are nitrosamines?

Nitrosamines are a class of mutagenic impurities
produced by the reaction of a secondary or tertiary amine with a nitrosating agent. Nitrosamine impurities such as NDMA and N-nitrosodiethylamine (NDEA) are of concern due to their potential to cause cancer. 

The International Agency for Research on Cancer designates both NDMA and NDEA as probably carcinogenic to humans (Group 2A). This 
category is used when there is limited evidence of carcinogenicity in humans and sufficient evidence of carcinogenicity in experimental animals. This implies that there is lack of direct evidence that these compounds causes cancer in humans, nevertheless, their presence in medicines is deemed unacceptable.

How are nitrosamines created?

Nitrosamine formation involves a complex
nitrosation reaction that requires an amine source and a nitrosating agent. Nitrosation is the process of introducing the NO group into an organic molecule.

Nitrosamines can be formed by nitrosation of primary, secondary, or tertiary amines. However, secondary amines are the most likely to form nitrosamines. Tertiary amines cannot react directly with a nitrosating agent – they first cleave into secondary amines and then form nitrosamines.

Nitric oxide, sodium nitrite, dinitrogen tetroxide and nitrous acid are some 
frequently used nitrosating agents. But, nitrosation can occur even without the presence of these agents. For example, some compounds such as sodium nitrate can act as indirect nitrosating agents under specific conditions. Exposure to reducing agents or oxidative conditions can also lead to nitrosation.

An acidic environment is usually required for nitrosation. However, nitrosation can occur in basic and neutral environment under the presence of catalysts such as aldehydes.

The nitrosating agent can be introduced during any stage of the drug manufacturing process. Identifying the source of contamination is thus challenging and may necessitate analyzing the entire supply chain. Below are some
possible scenarios that may result in the introduction of nitrosamine impurities:

  • Side reactions from drug syntheses
  • Breakdown of unstable drug compounds
  • Contamination from recycled solvents used in manufacturing 
  • Improperly cleaned reactors which may leave traces of the nitrosating agent 
  • Drug packaging. Low levels of NDMA have been detected in blister packaging under certain conditions.

The vast possibility of sources mandates the manufactures to implement robust strategies to evaluate and mitigate potential risks.

How are nitrosamine impurities detected?

Nitrosamine impurities occur at microgram levels. Hence, sensitive and specific analytical
techniques are required for their detection. The amount of impurities detected in drug products can vary widely depending on who performed the test, the drug manufacturer and the specific batch tested.

Gas chromatography (GC) coupled with thermal energy analysis or mass spectrometry (MS) can be used to
detect heat-sensitive nitrosamine impurities. GC coupled with MS is reported to have high selectivity and sensitivity.

Another option is the use of liquid chromatography (LC) coupled with thermal energy analysis, MS or ultraviolet light (UV). LC can be used for both volatile and non-volatile nitrosamines.
High-performance liquid chromatography (HPLC) and UV can help analyze low-dose drugs.

Medicinal products with nitrosamine impurities detected

Sartans were the first class of medicines in which nitrosamine impurities were discovered. A modification in the synthetic process for the active pharmaceutical ingredient (API) was identified as the underlying cause of this contamination. Shortly after the
valsartan recall, irbesartan and losartan were found to contain NDMA and NDEA. 

The discovery of nitrosamine impurities in commonly prescribed drugs prompted regulatory authorities to implement a rapid response. The US Food and Drug Administration (FDA) and European Medicines Agency (EMA) published
interim limits several nitrosamine impurities, including NDMA, NDEA and N-methyl-4-aminobutyric acid (NMBA), in sartan products.

Ever since the temporary limits were established, nitrosamine impurities have been found in drug products outside the sartans. Impurities have been discovered in a few batches of 
pioglitazone, a drug approved for the treatment of diabetes, and ranitidine, a popular antacid. Nizatidine is another antacid recalled due to the presence of nitrosamines. 

Nitrosamines have also been found in metformin, a widely used diabetes drug. As of January 2021, around
250 products containing metformin have been recalled in the US. 

Analysis of Genotoxic Nitrosamines in Losartan

The US Food and Drug Administration (FDA) and the European Medicines Agency (EMA) continue to closely monitor nitrosamine levels in pharmaceutical products since the initial discovery of N-nitrosodimethylamine (NDMA) in valsartan in 2018 prompted recalls of the drug. These recalls highlight the ongoing need for sensitive, selective methods for the analysis of multiple nitrosamines in pharmaceutical products prone to contamination by these potentially carcinogenic compounds. Download this app note to discover a system that demonstrates good chromatographic separation of nitrosamine compounds with enhanced sensitivity.

View App Note

Steps taken by health authorities to anticipate and prevent product recalls in future

The discovery of nitrosamines in widely prescribed drugs has raised several concerns, with patient safety being of utmost importance. These concerns compelled health authorities to take steps to anticipate and prevent such unforeseen product recalls in the future.

Regulatory agencies have released guidelines instructing the drug manufacturers to conduct risk evaluations of all drugs and evaluate the manufacturing processes to detect any risk of creating 
N-nitrosamine impurities. 

Giovanna Rizzetto
, senior manager at the European Federation of Pharmaceutical Industries and Associations (EFPIA), explains, “The key is to apply the existing provisions of ICH M7 (control of mutagenic impurities) and ICH Q9 (quality risk management) and Good Manufacturing Practice (GMP). This provides a framework to identify, assess and develop controls that should be used for nitrosamines. This framework requires the application of scientific principles by experts in chemistry and manufacture and the oversight of manufacturing operations by regulators through inspection.”

Drug manufactures are responsible for thoroughly understanding their manufacturing processes, including steps to detect and prevent the presence of unacceptable levels of impurities. 

“Scientific understanding of how nitrosamines can form and purge is an emerging field, and so it is important that manufacturers’ experts apply the best possible understanding to evaluate and address risks. In practice, this means reviewing how drugs are chemically synthesized and examining the materials used to manufacture the active drug substance and the formulated drug product, as well as ensuring that controls are developed to minimize the risk from nitrosamines at the appropriate points. Regulators such as the EMA regularly publish and update guidance on the potential root causes of nitrosamine formation, and there have been a number of significant publications in peer-reviewed chemistry journals by drug manufacturers which have advanced the science,” 
says Rizzetto.

What basic steps can drug manufacturers take to prevent higher levels or eliminate N-nitrosamines?

The detection of nitrosamine impurities can be challenging for drug manufacturers. The pharmaceutical supply chain is complex – APIs, excipients and raw materials can come from various locations around the world. Another challenge is the complexity of the manufacturing process. However, manufacturers can take steps to control the risk.
“All products and manufacturing processes are different, so manufacturers need to use scientific assessment to review where nitrosamines might be formed during manufacture, take appropriate steps to investigate and introduce controls if needed. This means examining the chemical steps used to manufacture a drug, the drug product formulation and the materials used,” says Rizzetto.

Once a manufacturer knows where nitrosamines can form as impurities, they can develop controls or make changes to the process to prevent them from forming, or alternatively, put measures in place to ensure they are removed.

Rizzetto continues, “
Sometimes, nitrosamine-forming chemicals have to be used in manufacture, but even then, the risks can be controlled if they are understood, and steps can be taken to control nitrosamines through changes to the synthesis. A good example is from the case of valsartan, where it was shown that nitrosamine-forming chemistry is a much more significant risk where it is employed late in a drug’s manufacturing process (e.g., in the last of a series of chemical reactions) and that nitrosamines formed in earlier steps can be purged.”

Safeguarding public health is always the priority

The drug recalls caused significant
concern among the patient community, which also impacted treatment adherence. However, health authorities urged patients not to stop their medication regimens without consulting their treating physician, as discontinuation could cause more damage to their health than the exposure to the unacceptable levels of nitrosamine impurities.

 says, “Patients should be assured that manufacturers have taken significant steps to fully understand and investigate nitrosamine risks in medicines and that the regulated frameworks (which focus on patient safety) are working to ensure medicines are of the highest possible quality. That said, nitrosamines are low risk if they are present in low enough levels and are actually present in many foodstuffs. It’s therefore important that patients understand the relevance of the levels seen and that risks are put in context.” 

Lessons learned 

The recall of vital prescription medicines raised several critical issues and made it crucial to maintain a safe supply of medications to safeguard patient health.  

In 2021,
Ilijana Sedlo, of the University of Rijeka and colleagues published a review paper on nitrosamine impurities in medicine products.  The paper outlines the causes and sources of nitrosamine impurities in medicinal products, the regulatory responses and the impact of drug recalls in Croatia.

“After the detection of N-nitrosamine in sartans, most active substance manufacturers who detected N-nitrosamine contaminants in their active substances were able to conduct a better investigation of the cause,” explains Seldo. These product recalls highlighted the need to increase the quality of manufacturing processes and the safety of medicines for future generations.

“Drug production and monitoring are constantly being raised to a higher level, there is no room for error – at least not in the long run,” concludes Sedlo.