Nitrosamine mitigation: NDMA impurity formation and its inhibition in metformin hydrochloride tablets

Abstract

The mitigation of nitrosamine formation in drug products has been studied and approaches such as using formulations with pH modifiers and antioxidants have been shown to decrease the formation of nitrosamines. However, more studies are needed to explore the effectivness of mitigation strategies with different drug models and formulations. The primary objective of this work was to assess the role of different antioxidants and pH modifiers in tablet formulations to mitigate the formation of NDMA, prepared in-house, using metformin hydrochloride as a model drug. A study design for manufacturing metformin hydrochloride formulations was created to evaluate potential mitigation stratigies. The formulations were prepared by wet granulation that included a sodium nitrite spike and various antioxidants such as ascorbic acid, caffeic acid and ferulic acid at various concentrations that may inhibit nitrosamine formation. The study design also included pH modifiers such as hydrochloric acid and sodium carbonate. The metformin hydrochloride formulations were placed under stability conditions that included humidity, temperature and time over a six month period. NDMA inhibition was found to be most effective in formulations with basic pH, followed by the addition of tested antioxidants with 0.1% concentrations in the formulations. All tested antioxidants showed complete mitigation in formulations with 0.5% and 1% concentrations. In summary, basic pH and the inclusion of antioxidants exhibited the potential to mitigate the formation of NDMA in metformin hydrochloride tablets.

Introduction

Metformin hydrochloride (HCl) is an oral drug prescribed for the treatment of type 2 diabetes mellitus (T2DM) (Hao et al., 2023, Kinaan et al., 2015, Marshall, 2017). Metformin HCl has become the most widely prescribed medication either used alone or in combination with other drugs for lowering blood glucose levels (Blonde et al., 2018, Kinaan et al., 2015). In 2020, the US FDA has recommended a voluntary recall of some of extended release (ER) metformin HCl drug products due to the presence of N-nitrosodimethylamine (NDMA) above the acceptable daily intake level of 96 ng/day (Administration, U.S.F.a.D, 2023, Administration, U.S.F.a.D., 2018a, Administration, U.S.F.a.D., 2021). More metformin HCl ER products were recalled during 2021, 2022, and 2023(Adminstration, U.F.a.D., 2021a, Administration, U.S.F.a.D., 2018b, Adminstration, U.F.a.D., 2021a, Agency, 2020).

The metformin HCl drug substance is synthesized by the reaction of dimethylamine hydrochloride (DMA) with dicyandiamide, heated to 120°C–140°C (Fig. 1) (Doomkaew et al., 2014; PIN, 2019; ZHANG, 2012). N, N-dimethylformamide (DMF) is one of the reactant solvents used in the synthesis of metformin HCl drug substance (ZHANG, 2012).

The formation of NDMA in metformin HCl drug products is due to residual DMA (also referred to as metformin impurity F in the European Pharmacopeia monograph) present in metformin HCl drug substance after synthesis (Fritzsche et al., 2022, Hao et al., 2023). In addition to residual DMA, DMF when used as a solvent under higher temperature conditions can undergo hydrolysis or de-carbonylation reactions to produce DMA (Cottineau et al., 2011, Magtaan et al., 2019, Thaore and Gaikar, 2013, Yang et al., 2020). Thus, DMA is a secondary amine impurity present in metformin HCl drug substance, that can react with a nitrosating agent [e.g., acidium ion (H2NO2+) or dinitrogen trioxide (N2O3) generated from nitrite (NO2–) under acidic conditions] to form NDMA (Boetzel et al., 2023, Hao et al., 2023). Nitrates and nitrites have been detected in commonly used pharmaceutical excipients including lactose monohydrate, crospovidone, magnesium stearate, povidone, hypromellose (HPMC) and microcrystalline cellulose (Bayne et al., 2023, Boetzel et al., 2023, Wu et al., 2011).

NDMA is a possible human carcinogen whose presence in drug products has led to product recalls in recent years (Administration, U.S.F.a.D., 2018a, Hao et al., 2023). For example, starting in 2018, numerous valsartan drug products [angiotensin II receptor blockers (ARBs)], used for the treatment of high blood pressure, were recalled due to the detection of NDMA above the acceptable intake limit (AI) of 96 ng per day (Administration, U.S.F.a.D., 2018a, Administration, U.S.F.a.D., 2018b, Fritzsche et al., 2022, Hao et al., 2023). Also, in 2020, all ranitidine drug products were recalled from the US market due to NDMA content above the AI (Adminstration, U.S.F.a.D., 2020). Various regulatory agencies including the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA) provided guidance to drug manufacturers detailing the root causes of NDMA and other nitrosamines and recommended to industry to conduct a risk assessments of drug substances and drug products for the potential to form N-nitrosamines (Adminstration, U.S.F.a.D., 2021, Agency, 2020).

As part of a risk assessment various mitigation strategies were considered to reduce NDMA formation in metformin HCl. One strategy includes the use of excipients from suppliers that contain low nitrite content, since nitrite is a key contributor to NDMA formation in metformin HCl (Hao et al., 2023, Schlingemann et al., 2022a). In addition, antioxidants have also been shown to be effective in reducing the formation of N-nitrosamines in drug products and have been recommended as a potential N-nitrosamine mitigation strategy (Administration, 2021; Aishwarya et al., 2024, Bayne et al., 2023, Hao et al., 2023, Nanda et al., 2021, Shakleya et al., 2023).

Two reaction mechanisms have been proposed by which antioxidants inhibit N-nitrosamine formation. The first mechanism involves a redox reaction, where antioxidants act as nitrite scavengers by reducing the nitrosating agent N2O3 to nitric oxide (NO), a non-nitrosating molecule. The second mechanism involves a nitration reaction, where antioxidants react with nitrites to form nitrophenols (Bayne et al., 2023, Hao et al., 2023, Homšak et al., 2022, Nanda et al., 2021). According to the Toxic Substances and Disease Registry (ATSDR) and the Environmental Protection Agency (EPA), The most common effects of 4-nitrophenol noted at lethal doses in animals are clinical signs of respiratory distress and neurotoxicity. Examples of antioxidants that have been shown to be effective in reducing N-nitrosamine formation in drug products include ascorbic acid (vitamin C), α-tocopherol (vitamin E), caffeic acid, ferulic acid and propyl gallate (PG) (Bayne et al., 2023, FDA, U., 2021, Hao et al., 2023, Nanda et al., 2021). Recent studies reveal that PG significantly reduces NDMA formation when added to metformin HCl formulations as compared to other antioxidants such as butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) (Hao et al., 2023b). Our recent studies have shown that the addition of 1 % w/w antioxidants (ferulic, ascorbic, or caffeic acid) to crushed bumetanide tableted formulations spiked with nitrite (500 ppm) in a stress environment (50 °C/75 % RH) reduced the formation of N-nitrosobumetanide (NBMT) compared to formulations that did not contain antioxidants. In the bumetanide studies, ascorbic acid showed the most reduction of NBMT formation among tested antioxidants.

Shakleya et al., 2023) The studies also reveal that the addition of ferulic, ascorbic and caffeic acid at concentrations of 1 %, 0.1 % and 0.5 % (w/w) reduced NBMT content in formulations of bumetanide generated in-house and spiked with nitrite (100 ppm) with 1 % showing the strongest effect (Shakleya et al., 2023). These manufacturing studies suggest that the addition of antioxidants to drug products is a promising mitigation strategy to reduce the formation of NDMA and other N-nitrosamines. However, as noted in the previous study, the inhibitory effect of antioxidants was dependent on the type and concentration of antioxidant.

The formulation of drug products under basic pH conditions has been shown to prevent NDMA and other N-nitrosamines formation in drug products (Hao et al., 2023, Shakleya et al., 2023). Inhibition of nitrosamine formation by the pH of the formulation is attributed to the fact that, typically, acidic conditions are required to convert nitrites to nitrosating agents (H2NO2+ or N2O3) that further react with susceptible amines (secondary or tertiary amines) to form N-nitrosamines (Fritzsche et al., 2022, Schlingemann et al., 2022a). Recent studies showed that NDMA formation in metformin HCl drug products was significantly reduced when formulation conditions were modified to a pH above 9 using Na2CO3 (Hao et al., 2023b). Our recent studies also revealed that the formation of NBMT was significantly reduced in bumetanide in-house model formulations spiked with nitrite (100 ppm) when the pH was adjusted to 9 using Na2CO3.(Shakleya et al., 2023) These data strongly suggest that the addition of antioxidants and adjustment of formulation pH to basic conditions can effectively prevent the formation of NDMA and potentially other N-nitrosamines in drug products.

The current study is aimed at investigating the ability of different pH modifiers (hydrochloric acid and sodium carbonate) and antioxidants (ferulic, ascorbic, and caffeic acid) to reduce NDMA formation in metformin HCl extended release (ER) throughout the manufacturing process. In this work, metformin HCl tablets were manufactured using a wet granulation process (Hao et al., 2023, Schlingemann et al., 2022a, Vidyapeeth, 2010). The wet granulation process involves a wet granulation step that includes the metformin HCl drug substance mixed with a binder solution or water in a high shear mixer or granulator, followed by drying, blending, and tableting steps (Hao et al., 2023, Schlingemann et al., 2022a, Vidyapeeth, 2010). The experimental objective was to determine if the wet granulation process may play a role in the formation of NDMA in metformin HCl drug products. In this study metformin HCl ER formulations were pre-spiked with nitrite, DMA, pH modifier (hydrochloric acid and sodium carbonate) and three different antioxidants (ferulic, ascorbic and caffeic acid) during the wet granulation step. The levels of nitrite, nitrate, DMA and NDMA in the model metformin HCl tablets were evaluated for a period of 6 months under three different stability conditions (25 °C/60 % relative humidity, 40 °C/75 % relative humidity and 50 °C/75 % relative humidity) to determine the inhibitory effects of the antioxidants and a pH modifier, in mitigating NDMA formation in metformin HCl drug products.

Metformin HCl was used as a model drug in evaluating the effect of pH modifiers and antioxidants in mitigation of NDMA formation in drug products. Although previous studies have shown the inhibitory effect of ascorbic acid, caffeic acid and ferulic acid on nitrosamine drug substance-related impurities, NDSRIs (nitrosamine impurity with the related chemical structure as the drug substance), the effectiveness of these antioxidants on reducing NDMA formation from DMA impurities in drug products has not been studied (FDA, U., 2021, Nanda et al., 2021, Shakleya et al., 2023).

Materials

Metformin HCl extended-release tablets 500 mg manufactured by a Generic house was procured from Brookville pharmacy and wellness center (Chevy Chase, MD, USA). Metformin HCl drug substance was obtained from Ria International LLC (East Hanover, NJ, USA). Microcrystalline cellulose Avicel PH102 was purchased from Ingredient Depot (Beauharnois, Quebec, Canada). Magnesium stearate, Povidone K-30, Hypromellose K100L VCR, colloidal silicon dioxide, ascorbic, caffeic and ferulic acid.

Diaa Shakleya, Alaadin Alayoubi, Dustin Brown, Alaa Mokbel, Nicolas Abrigo, Adil Mohammad, Jiang Wang, David Li, Maha Shaklah, Fahd M. Alsharif, Saaniya Desai, Martha Essandoh, Patrick J. Faustino, Muhammad Ashraf, Thomas O’ Connor, Matthew Vera, Andre Raw, Vilayat A. Sayeed, David Keire, Nitrosamine mitigation: NDMA impurity formation and its inhibition in metformin hydrochloride tablets, International Journal of Pharmaceutics, 2024, 124832, ISSN 0378-5173, https://doi.org/10.1016/j.ijpharm.2024.124832.

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