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  4. Bumetanide as a Model NDSRI Substrate: N-nitrosobumetanide Impurity Formation and its Inhibition in Bumetanide Tablets
  1. News & Events for Human Drugs

Bumetanide as a Model NDSRI Substrate: N-nitrosobumetanide Impurity Formation and its Inhibition in Bumetanide Tablets

Background

Nitrosamine drug substance-related impurities (NDSRIs) (a class of nitrosamines that are associated with or share structural similarity with the active pharmaceutical ingredient [API] of a drug) present scientific and regulatory challenges because each NDSRI is generally unique to the API, and there is limited compound-specific data to inform safety assessments. NDSRIs can form during manufacturing or during the shelf-life storage period of a drug product. As such, control strategies to mitigate the risk of NDSRI formation should be tailored to the drug.

N-nitrosobumetanide (NBMT) is a known NDSRI that may form in bumetanide (BMT) (a drug used to treat fluid retention and swelling caused by certain medical conditions). If NBMT is formed during API synthesis, it may be removed through purging in later steps in the synthesis or through additional purification. But if NBMT forms during drug product manufacturing or storage, it cannot be purged. Therefore, making modest changes to the drug formulation may inhibit the risk of NBMT formation and improve the safety profile of products containing BMT.

Two approaches previously recommended by CDER to mitigate small-molecule nitrosamine (nitrosamines that do not share structural similarity to the API) formation in drug products during formulation include the use of antioxidants (inhibitors) or increasing the pH of the product formulation. But limited research on these control strategies exists for NDSRIs.

To that end, CDER researchers conducted a study1 to evaluate pH adjustment and addition of antioxidants in tablet formulations prepared in-house using BMT as a model drug product to mitigate the formation of NBMT. These results were shared in the peer reviewed scientific literature to provide drug makers with approaches to prevent or minimize NDSRI formation in their drug products.

Study Design

To set the stage for the study, the CDER research team conducted initial screening studies to determine the extent and rate of formation of nitrosamine impurities in a marketed BMT drug product. The researchers then prepared in-house BMT immediate release tablets with common excipients (i.e., inactive ingredients) by the wet granulation process based on the initial screening data from the marketed BMT drug product studies. Tablets were chosen for this study because several BMT products are made as tablets where nitrosamine formation can occur during the drying of the wet granulation step of tablet manufacturing.

Twenty-six in-house formulations were prepared, where different levels (0.1, 0.5 or 1% w/w) of antioxidants (ascorbic acid, caffeic acid, or ferulic acid) and different pH levels (acidic = 0.1N hydrochloric acid and basic = 0.1N sodium bicarbonate) were added.

Two variations of each formulation (manufactured BMT tablets) were prepared with one sample being spiked with an excess of sodium nitrite to stimulate nitrosamine formation and enable better detection of the potential mitigation effects of the antioxidants and pH modifiers.

The 26 samples were stored in stability chambers that differed in temperature and humidity at two conditions commonly used to assess drug stability for up to six months:

  • Accelerated: 40 °C/75% Relative Humidity (RH)
  • Long-term: 25 °C/60% RH

Results

In all four sample types of the in-house formulated tablets (the long-term stability samples with and without excess added nitrite; accelerated stability samples with and without added nitrite), all three antioxidants (ascorbic acid, caffeic acid, and ferulic acid) showed effective mitigation of NBMT formation. Among the antioxidants, ascorbic acid showed the highest inhibition of NBMT formation followed by caffeic acid, and then ferulic acid. In addition, increasing antioxidant concentration improved NBMT mitigation with highest (1%) antioxidant amount showing the greatest inhibition of NDSRI formation.

The content of NBMT in the stability samples with antioxidants and nitrite added showed some increase in the first month at the long-term storage condition (25 °C /60% RH) and then decreased up to six months. However, samples stored at the accelerated condition (40 °C /75% RH) mostly showed decreased NBMT amounts during storage. For the long-term storage conditions used in the study the increase of NBMT in the first month showed that there was some formation of the NDSRI over time. The observations of decreased NBMT amounts in the tablets suggested a breakdown of NBMT over time under both conditions.

Making the pH environment of the samples more basic (increasing the pH) by adding sodium bicarbonate had the highest overall inhibition of nitrosamine formation even as compared to the best antioxidant performer, ascorbic acid. In contrast to the observations with antioxidants there was no significant change in the amount of NBMT observed in samples with sodium bicarbonate added under accelerated or long-term storage conditions.

Discussion

In the last couple of years, several NDSRIs have been reported for different drugs leading to product recalls. Because of the cancer-causing potential of nitrosamines, it is critical that manufacturers of APIs and drug products take steps to prevent unacceptable levels of these impurities in drug products or avoid their presence when possible.

Compared to small-molecule nitrosamines, less is known about potential strategies to control or mitigate NDSRIs in drug products. Previous research had focused on inhibition of formation of small-molecule nitrosamines with antioxidants using experiments in liquids. In that same vein, more recent studies were performed on metformin tablets but were focused on preventing small-molecule nitrosamine formation and not on NDSRIs like the study described here.

Ascorbic acid, caffeic acid, and ferulic acid were selected as the study antioxidants based on prior research that demonstrated their capability to inhibit nitrosamine formation. In addition, because nitrosamine formation can occur under acidic conditions during the drug formulation process, another control strategy that was applied to inhibit nitrosamine formation was increasing the pH of the drug formulation to basic conditions.

The results of this study demonstrate that the addition of antioxidants or compounds that make the pH environment basic in the formulation of BMT drug products can effectively inhibit the formation of NBMT. The type and amount of antioxidant used also had a significant impact on the effectiveness of the inhibition of NBMT formation. More broadly, pH adjustment or addition of antioxidants to drug product formulations are possible approaches to prevent or mitigate NDSRI formation in other drugs that have the potential to form them.

This research helped support CDER’s Control of Nitrosamine Impurities in Human Drugs guidance by providing manufacturers with potential approaches to drug formulation to mitigate or prevent formation of NDSRIs in solid state (tablet) drug products.

1Shakleya, D, Asmelash, B, Alayoubi, A, Abrigo, N, Mohammad, A, Wang, J, Zhang, J, Yang, J, Marzan, TA, Li, D, Shaklah, M., Alsharif, FM, Desai, S, Faustino, PJ, Ashraf, M, O'Connor, T, Vera, M, Raw, A, Sayeed, VA, and Keire, D, 2023, Bumetanide as a Model NDSRI Substrate: N-nitrosobumetanide Impurity Formation and its Inhibition in Bumetanide Tablets. J Pharm Sci, 112(12), 3075–3087. https://doi.org/10.1016/j.xphs.2023.06.013

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