While the topic of nitrosamines in drug products continues to be a widely discussed topic, there is still no guidance or mandated maximum allowable levels of nitrosamines, or their precursors, in pharmaceutical waters.  Several groups and agencies have suggested that water is a potential source of nitrosamine contamination in drug products, but again, no specific limitations on these compounds have been proposed for water.  We had recently discussed the sources and risks associated with the presence of nitrosamines in pharmaceutical waters here: 

Nitrosamines in Pharmaceutical Waters: Origins, Risk Mitigation, and Testing Requirements

Since, additional guidance has been proposed regarding testing requirements for potable water.  The draft copy of the “WHO good manufacturing practices considerations for the prevention and control of nitrosamine contamination in pharmaceutical products” (April 2024) suggests additional testing for nitrosamines and nitrosating agents in potable water as follows:

“Potable water is sometimes used in the production of materials such as excipients and APIs; or to clean equipment. Water may contain low levels of chloramine and or nitrites/nitrates, which are known to potentially react with secondary amines to form nitrosamine impurities, depending on specific conditions. The source, quality and purification of water may impact on the absence, presence or formation of nitrosamine impurities. For example, chlorination may contribute to the formation of nitrosamine impurities. Chloramine, nitrite/nitrate and nitrosamine levels in water should thus be determined. 

Where required, water should be purified to remove unacceptable impurities before use.”

Potable water is often used in initial stages of drug manufacturing as well as preliminary cleaning and rinse steps for product contact surfaces.  It is also the starting ingredient of any compendial water.  Current testing requirements for any water used for pharmaceutical purposes ensures that the quality meets potable water standards, specifically the EPA National Primary Drinking Water Regulations or comparable potable water standard.  This is outlined in USP monographs for pharmaceutical waters and is consistent with other international pharmacopoeiae.

Water used for production of finished pharmaceuticals, such as Purified Water and Water for Injection (WFI), must meet higher quality standards.  Treatment of potable water used in pharmaceutical applications may include activated carbon, reverse osmosis, ion-exchange processes, as well as additional purification processes such as UV light or ozone.  Compounded, these treatment processes reduce the levels of chloramines, nitrates and nitrites, and nitrosamines, to levels either undetectable by routine chemistry tests or in the parts per million or parts per billion ranges.

This proposed guidance from the WHO for nitrosamine testing in potable waters used in pharmaceutical applications is logical  Potable water standards are not universal, chloramination is a common microbial control technique used by municipalities in the U.S., and naturally occurring nitrogen compounds can vary be present in feed waters.  However, the suggested testing may not extend to compendial waters.  Treated to meet standards and levels for other critical quality attributes, the concentrations of these compounds are likely within acceptable limits.  A risk assessment can be used to determine if additional sampling or monitoring is required. 

Risk Assessment considerations when developing test plans for nitrosamines and their precursors may include the following:

• Presence of chlorine and chloramines – These residual disinfectants found in feed waters are nitrosating agents that can react with amines to form nitrosamine compounds.
• Nitrite / nitrate levels – The presence of these compounds can lead to formation of nitrosamines as part of the water treatment process or when present in the product water, may lead to formation of nitrosamine impurities during drug synthesis
• Purity level of water or purification techniques used – The more the water is purified to remove other organic and inorganic impurities, the lower the expected concentrations or nitrosating agents and nitrosamine precursors should be.
• Anion exchange resin used as a treatment process – The use of ion-exchange resins as part of the treatment process, may actually increase the concentration of amines.  In particular, strong base anion resins, which may elute quaternary amines, can lead to nitrosamine formation.
• Ozonated Systems – The presence of nitrogen compounds, especially nitrite and nitrate, may lead to nitrosamine formation.  
• Water contribution to or presence in the final product – The amount of water used in product formulation, or the water activity for non-sterile products, should also be considered.  In some instances, such as when the water is only used for cleaning and sanitization, then the risk of contribution of nitrosamines in the final product may be minimal.  Both FDA and EMA have provided guidance on daily allowable intake (AI) levels for nitrosamine impurities in drug substances.  A risk assessment should include an evaluation of how the water is actually used in the drug manufacturing process.
• History of high nitrate levels – Most Purified Water and WFI sampling programs have historically included testing for nitrates as required by the European Pharmacopoeia (EP).  Although this testing requirement was recently removed from the EP water monographs, if high levels of nitrates have been observed, additional testing for these compounds and nitrosamines would be warranted.  

A definitive specification for nitrosamine levels in Purified Water and WFI may never be promulgated.  Although AIs for specific nitrosamine compounds in finished pharmaceuticals are now being introduced, maximum contaminant levels for these impurities in pharmaceutical waters are not expected.  Regardless, by its nature, water remains a potential source of nitrosamine contamination and some level of testing is warranted.