(T1230-09-59) Risk Mitigation of Nitrosamine Impurities in Drug Products Containing Secondary Amine APIs Through Excipient Nitrite Control

Purpose: Nitrosamine impurities are carcinogenic contaminants of concern in pharmaceuticals, particularly in drug products containing secondary amine APIs. Nitrosation reactions can be triggered by nitrosating agents such as nitrous acid, N₂O₃, N₂O₄, and nitrosonium salts, often originating from nitrite-containing excipients. This study aims to demonstrate effective strategies to mitigate nitrosamine impurities, emphasizing the impact of excipient nitrite content even within the same grade from different sources and the importance of comprehensive raw material evaluation and supplier management incorporating validated nitrite testing.

Methods: The API and formulation ingredients (Table-I) were co-sifted through a #30 mesh and blended in a bin blender followed by lubrication with Mg. stearate after passing it through #40mesh.The lubricated blends were then compressed into tablets with help of Korsch XL-100 tablet press. Subsequently, the favorable formulation was scaled up to a batch size of 150,000 tablets using a Korsch XM-12 tablet compression machine for ANDA submission. Formulations A and B were manufactured using MCC with unmonitored Nitrite content, with Formulation B also incorporating an oxygen scavenger. Formulation C explored the use of ascorbic acid (DC Fine Chemicals, Spain) as a nitrite scavenger, while Formulation D replaced MCC with Dicalcium Phosphate Dihydrate (Innophos, USA) as an alternative diluent.Formulation A was successfully scaled up and was found to be bio-equivalent with the Reference Listed Drug (RLD). To address elevated nitrosamine levels in the filed drug product submitted to the FDA (Formulation A), regular MCC was substituted with low-nitrite MCC (Ceolus™, Asahi Kasei Corp., Japan) and the formulation was scaled-up to ANDA batch size. The drug product was evaluated for nitrosamine impurities using a validated LC-MS method.

Results: Nitrosamine impurities are often degradation products that can increase over the shelf life of a drug product. Per FDA guidance, the permissible limit for nitrosamine impurities in drug products is 150 ppm. The bioequivalent batch (Formulation A) was evaluated for N-nitroso impurities at the 6-month accelerated stability timepoint, yielding a result of 110 ppm, which is approximately 75% of the allowable threshold. In response, additional formulation trials were undertaken to establish further control strategies aimed at minimizing nitrosamine formation. Various laboratory-scale formulations were developed (Table I). For Formulation A, nitrosamine levels increased from approximately 30 ppm at initial testing to 110 ppm at 6 months under accelerated conditions. Incorporation of an oxygen scavenger into Formulation A led to a modest reduction in nitrosamine levels, likely due to decreased oxygen availability for nitrosation reactions. The addition of ascorbic acid significantly reduced nitrosamine content; however, this change would require a new bioequivalence study. In contrast, substituting microcrystalline cellulose (MCC) with dicalcium phosphate resulted in elevated nitrosamine levels that approached the regulatory limit even at the initial timepoint. A significant reduction in nitrosamine impurity levels upon replacing regular MCC with a low nitrite MCC (Ceolus™) in Formulation A has been observed. Despite of the MCC substitution, Formulation A maintained similar critical quality attributes of tablet compressibility, disintegration, assay and impurity level as original bio-relevant formulation. The scale up batches Nitrosamine levels were further monitored under stability conditions (Table II). Formulation A, when prepared using low-nitrite MCC (Ceolus™), exhibited an approximate 40% reduction in nitrosamine content after 6 months at accelerated stability conditions. These results underscore the critical influence of excipient nitrite content on nitrosamine formation.

Conclusion: This study demonstrates that N-nitroso impurities in finished drug products, including those containing secondary amine APIs, can be effectively controlled by minimizing nitrosationduring formulation. The mitigation strategy incorporates several key elements: the use of nitrite and oxygen scavengers, optimization of excipient combinations, and critically, the selection of excipients with verified low nitrite content.This study highlights that excipients of the same grade can vary in their impact on nitrosamine formation due to differences in manufacturing process and nitrite content. To mitigate nitrosamine risk, drug product manufacturers should supplement pharmacopeial specifications with validated nitrite testing and thorough supplier qualification.

Table-I: Formulation Composition with Nitrosamine Impurity Levels

Table-II: Nitrosamine Levels under Accelerated Stability