Manufacture of API
Potential causes of the contamination of active pharmaceutical ingredients (API) and/or proprietary medicinal products during the manufacture of API and observations connected with these contamination sources are listed below:
1. Specific reaction conditions in the presence of certain raw materials and starting compounds:
Nitrosamines can occur under suitable reaction conditions in the presence of certain raw materials (including starting compounds and intermediates) and, in the event of inadequate purification and incomplete purging in the subsequent steps of the manufacturing process for an API, can be carried over into the medicinal product as an impurity.
2. Sodium nitrite (NaNO2) or other nitrites in the presence of secondary or tertiary amines:
NaNO2 or other nitrite salts can form nitrosamines in the presence of secondary or tertiary amines under suitable reaction conditions (e.g. pH, temperature). Other conceivable causes for the formation of nitrites in the synthesis process include the reduction of nitrates or nitric acid, chlorination of urea or ammonia, cleavage of organic nitrates and conversion to nitrites under reductive conditions.
Secondary amines can be used as synthesis components, reagents, catalysts or solvents. They can also exist as a constituent of the molecular structure of the API itself or its intermediates or as impurities or degradants in raw materials or can form during the actual process. For example, amide solvents can be degraded to secondary amines. Known sources of secondary amines include N,N-dimethylformamide [DMF], N-methylpyrrolidone [NMP] or N,N-dimethylacetamide [DMA].
Tertiary amines used in synthesis chemistry include common bases, whose involvement in the formation of nitrosamines has already been observed (e.g. triethylamine, diisopropylethylamine [Hünig's base, DIPEA]). However, other less common bases are sometimes used in manufacturing processes, e.g. N-methylmorpholine (NMM) or tributylamine (TBA) and many others that could lead to the formation of various nitrosamines.
Secondary and tertiary amines might also be present as impurities or degradants of quaternary ammonium compounds such as tetrabutylammonium bromide (TBAB) or also in primary amines such as monoethylamine.
This list of possible sources is not exhaustive, since many other reagents with amino groups as well as catalysts or solvents can be used for a wide variety of synthesis steps. Other reagents with functional amino groups should also be considered in the evaluation of the potential risk of nitrosamine formation.
In most confirmed cases of contamination to date, a nitrite and an amine were used in the same manufacturing step. However, other cases have been identified in which the sodium nitrite used in one step appeared in the subsequent synthesis stages despite extensive purification operations and then reacted with an amine to generate the nitrosamine impurities, and vice versa. Since the possibility of carry-over from one step to the next cannot be ruled out, all processes that use NaNO2 or that involve potential nitrite sources must be considered and evaluated in respect of the risk of the formation and subsequent carry-over of nitrosamine impurities if amines (see examples listed above) are present in a synthesis step.
3. Recovered or recycled material:
Contaminated raw materials in the manufacturing process can be a source of nitrosamines. Recovered or recycled material (e.g. solvents, reagents and catalysts) entails a risk of nitrosamine formation if the solvents, reagents or catalysts to be recovered or recycled contain amines and if they are subsequently treated with nitrous acid, e.g. in order to destroy residual azides without adequate control of the processes.
O-xylene and tributyltin chloride (as a source of tributyltin azide) are examples of recycled substances that can be contaminated by nitrosamines. It is also thought that DMF might be contaminated in this way.
4. Recovery by third parties:
The recovery of materials (e.g. solvents, reagents and catalysts) is often entrusted to third parties. Sometimes these external recovery companies do not receive sufficiently specific information about the composition of the materials treated by them, and they use routine treatment processes and generally accepted equipment. This can lead to cross-contamination of the solvents, reagents and catalysts (which originate from various sources and processes) if the equipment is not adequately cleaned between customer orders or if no precautions are taken to prevent nitrosamine formation.
5. Contaminated raw materials, including intermediates:
The presence of nitrosamines may also be caused by contaminated raw materials or intermediates from distributors that use conversion methods or raw materials that can lead to the formation of nitrosamines. For example, nitrites or amines are known to occur as impurities in raw materials, particularly in reagents, solvents or excipients that are also used in finished products.
In such cases, the contamination of raw materials, starting materials and/or intermediates procured from external suppliers then becomes problematic if the manufacturer of an API that exclusively employs processes in which no nitrosamines are formed is not aware that the risk of nitrosamine impurities even exists.
Technological excipients used in large quantities, such as industrial nitrogen (which is often used to clean containers, degas solvents or transfer liquids) and water, should also be considered as potential sources of nitrites or nitrogen oxides.
6. Defective optimisation of the manufacturing processes for an API:
A defective optimisation of the manufacturing processes for an API, i.e. unsuitable or poorly controlled reaction conditions in respect of temperature, pH or the order in which reagents, intermediates or solvents are added, can also lead to the formation of nitrosamine impurities. This may be the case particularly if there is inadequate knowledge of the synthesis pathway or the conditions during the manufacture of the API, thus resulting in the formation of nitrosamine impurities.
Medicinal product manufacture
The potential sources of nitrosamine contamination during the manufacture of a medicinal product and corresponding considerations are as follows:
- The risk of nitrosamine impurity formation during the manufacture and packaging of the medicinal product (such as when certain containers, API or packaging components come into contact with amines or nitrites, e.g. reaction of secondary amines in printing inks with certain nitrocellulose lacquers or coating materials when heated) should be considered in the risk evaluation.
- Processes in which constituents of the medicinal product containing nitrites or amines occur together in solution or in suspension (e.g. during granule manufacture) or are kept at high temperatures (e.g. during drying steps) can be associated with an increased risk of nitrosamine formation.
- Nitrosamines formed during the manufacture of a medicinal product, unlike the situation for API manufacture with multiple synthesis stages thanks to subsequent purification steps, are almost impossible to remove from the medicinal product.