An Overview of Nitrosated Drug Substance Related Impurities (NDSRIs)
Nitrosamines in Drug Substance (DS)
In 2018, health authorities first detected the nitrosamine N-nitrosodimethylamine (NDMA) in valsartan drug substance. Investigations quickly expanded, and NDMA along with other carcinogenic nitrosamines were found in other members of the sartan drug family. By late 2019, nitrosamines were also identified in drug substances like pioglitazone and ranitidine. Nitrosamines are classified as probable human carcinogens, part of the “cohort of concern” due to their cancer risk. Regulatory bodies have established acceptable intake (AI) limits for small nitrosamines ranging from 26 to 100 ng/day (Ref. 3). In most cases, nitrosamine formation was linked to several factors such as the presence or formation of secondary amines, solvents, and reagents during the drug substance manufacturing process.
The NDMA source in ranitidine was unique and not linked to DS manufacturing. In April 2020, Emery Pharma identified that NDMA levels in ranitidine (Zantac) could increase significantly under elevated temperatures, a phenomenon not seen before in nitrosamine contamination. We submitted a citizen petition to the FDA, resulting in a nationwide recall. In this case, the nitrite source for the nitrosation reaction originated from the ranitidine DS structure itself—specifically, the vinyl nitro moiety.
Elevated NDMA levels were later found in certain metformin drug products, though not in the metformin drug substance. In February 2021, the FDA released its first guidance on nitrosamines (Ref. 3), emphasizing NDMA mitigation in drug substance manufacturing. At that point, drug substance manufacturing was considered largely de-risked. The guidance also briefly mentioned drug product nitrosamine formation, though no examples had been confirmed at the time.
Nitrosated Drug Substance Related Impurities -NDSRIs
Between 2021 and 2023, it became clear that nitrosation of secondary amines can occur uniquely in finished drug products. Common pharmaceutical excipients have been found to contain trace levels of nitrite ion (sub- to several ppm), such that a typical oral tablet may contain ~1 ppm nitrite (Ref. 1). If the drug substance contains a secondary amine moiety, reaction with this trace nitrite can form an NDSRI impurity (see Scheme 1).
(Scheme 1)
At least four drug products—varenicline, propranolol, quinapril, and dabigatran etexilate—have been voluntarily recalled due to NDSRI formation. In addition to direct nitrosation of DS secondary amines, secondary amine degradants (formed from parent DS without secondary amines) can also form nitrosamines. Examples include NDMA in metformin drug products and NDSRI-related recalls for rifampin, rifapentine, orphenadrine, and sitagliptin. At the time of these recalls, no established AI limits existed for these newly discovered NDSRI impurities.
In August 2023, the FDA released new guidance (Ref. 2) for setting AI limits for NDSRIs based on molecular structure. This applies to all approved and in-development drugs. The Predicted Carcinogenic Potency Categorization approach classifies structures into four AI categories ranging from 1500 ng/day to 27 ng/day (Table 1, Column 1). The FDA analyzed 263 marketed drug structures, modeled their potential nitrosated analogs, and assigned corresponding AIs. The distribution among these AI categories is summarized in Table 1, Column 2.
Column 3 estimates how much of the ~1 ppm nitrite in a 300 mg tablet (MW 300 g/mol) would need to react to reach each AI limit. In three out of four cases, only 20% or less of the nitrite must react to exceed the allowable threshold. Column 4 compares these AI values to the ICH Q3B 0.1% impurity threshold, revealing that most NDSRI AI limits are 30–2000 times more stringent.
Drug sponsors with marketed products must bring all affected drug products into compliance with Table 1 AI limits by the end of 2025 through risk assessments and confirmatory testing. All new NDA submissions must comply with these NDSRI limits at release and over shelf life. If an NDSRI approaches its AI threshold, detailed control strategies must be in place. Confirmatory testing for NDSRIs is especially likely if the impurity falls under one of the lower AI categories.
Emery Pharma can assist in managing the NDSRI risk in your drug product
Secondary amine containing DS. Emery Pharma can synthesize small quantities of the nitrosated analog of your DS early in development to help assess NDSRI formation risk. We have deep expertise in nitrosation drivers, including excipient reactivity, pH, and formaldehyde evolution (Ref. 4). We can help you develop robust mitigation and control strategies based on this early insight.
Tertiary amine containing DS. Tertiary amine drug substances are not without risk. About 10-15% of tertiary amines in DS will be able to undergo rapid de-alkylation upon nitrosation (Ref. 5). This results in a nitrosated secondary amine, with the same efficiently as direct secondary amine nitrosation. Another risk of tertiary amines is oxidation to the N-oxide which can result in formation of a secondary amine degradate. The secondary amine degradate can then nitrosate (examples above). This is shown in Scheme 2.
Our team can determine whether your tertiary amine DS is susceptible to de-alkylation or oxidation, and experimentally confirm it. We can also monitor and quantify the formation of these secondary amines and their corresponding NDSRIs at any level of detectability required by your project.
Tertiary amide DS. Hydrolytic degradation is common in solid dosage forms. A tertiary amide may be able to undergo hydrolysis more readily if the amide bond is activated. The result is a secondary amine which could nitrosate. This is shown generally in Scheme 3.
Emery Pharma applies predictive stress testing to determine whether your tertiary amide DS is at risk for secondary amine formation under stability conditions. If required, the secondary amine and its corresponding nitrosated impurity can be synthesized and quantified. If you need nitrosamine and NDSRI analysis services, please contact us online or call us at +1 (510) 899-8814!
References:
- Boetzel R. et al. “A nitrite excipient database: A useful tool to support N-Nitrosamine risk assessments for drug products”. Pharm. Sci. 2023 (112) 1615-1624.
- August 2023, FDA: “Recommended Acceptable Intake Limits for Nitrosamine Drug Substance Related Impurities (NDSRIs) Guidance for Industry”
- February 2021, FDA. “Control of Nitrosamine Impurities in Human Drugs- Guidance for Industry”
- Harmon P. “Trace Aldehydes in solid oral dosage forms as catalysts for nitrosating secondary amines” Pharm. Sci. 2023 (112) 1216-1219.
- Burns MJ et al. “Revisiting the landscape of potential small and drug substance related nitrosamines in pharmaceuticals” Phar. Sci. 2023 (112) 3005-3011
