Approaches and Considerations for the Investigation and Synthesis of N‑Nitrosamine Drug Substance-Related Impurities (NDSRIs)

N-Nitrosamine risk assessment of pharmaceuticals has moved from an initial focus on the potential presence of known small-molecule N-nitrosamines such as N-nitrosodimethylamine (NDMA) and N-nitrosodiethylamine (NDEA) in active substances toward the potential for generation of more complex nitrosamine drug substance-related impurities (NDSRIs) in drug products. While N-nitrosation of simple secondary amines is well-understood, more complex amines can undergo alternative reaction pathways that can be more challenging to predict. A number of such complex amines are known not to undergo N-nitrosation but are either unreactive or react by alternative pathways such as C-nitrosation or nitration to generate non-N-nitrosamine products. This article proposes a standard set of three orthogonal nitrosation forced degradation type reaction conditions that can be used to investigate the potential for generation of novel N-nitrosamines by nitrosation of complex amines. These complementary reaction conditions are considered to provide a thorough evaluation of the potential for N-nitrosamine formation from complex amines with respect to risk factors within pharmaceutical manufacturing. If, after investigation of nitrosation under the proposed conditions, formation and isolation of an N-nitrosamine is not possible, the resultant understanding of chemical reactivity and stability can be used to justify that the N-nitrosamine in question would not be expected to be generated from the complex amine in the drug substance or product. If an N-nitrosamine is formed under these reaction conditions, the information gained can be used as part of the risk assessment and also provides a starting point for the development of a process to synthesize a discrete sample for further testing. Additionally, synthetic and analytical considerations that should be taken into account during preparation of novel N-nitrosamines for use in analytical or toxicological studies are discussed.