FDA Issues Request for Comments on Nitrosamine Drug Substance-Related Impurities in Human Drug Products

On May 4, 2023, the U.S. Food and Drug Administration (FDA or the Agency) issued a Federal Register Notice (FRN) titled Identification, Assessment, and Control of Nitrosamine Drug-Substance Related Impurities in Human Drug Products, 88 Fed. Reg. 28,557 (May 4, 2023). This notice relates to FDA’s ongoing investigation into the presence of nitrosamine impurities in certain drug products, which began in June 2018, and supplements existing FDA guidance on manufacturers’ role in this investigation. FDA, Guidance for Industry, Control of Nitrosamine Impurities in Human Drugs (Feb. 2021) (Nitrosamine Guidance).

This is a meaningful development given the substantial scientific and regulatory uncertainty surrounding nitrosamine drug-substance related impurities (NDSRIs) and upcoming deadlines. FDA has recommended that all companies conduct confirmatory testing when there is a risk of nitrosamine impurities in active pharmaceutical ingredients, marketed products, and products under approved and pending applications, and report changes implemented to prevent or reduce the nitrosamine impurities on or before October 31, 2023. Following this process, companies have detected NDSRIs in their drug products, but the toxicological significance (if any) of these newly discovered NDSRIs is unclear. In the absence of any NDRSI-specific experimental data on potential mutagenic or carcinogenic risks, companies and regulators are relying on a limited set of tools to test for and predict toxicological risks that are not always fit-for-purpose. The FRN signals FDA’s interest in advancing predictive technologies, reducing testing burdens, and collaborating with industry—all of which have the potential to be significant steps forward in addressing the unique scientific and regulatory challenges presented by NDSRIs.

The FRN acknowledges these challenges and announces the establishment of a docket to solicit public comments on scientific and regulatory considerations regarding the identification, assessment, and control of NDSRIs in human drug products.

Comments are due July 3, 2023.

Safety Assessments of the Potential for Mutagenic and Carcinogenic Risk

The FRN explains that the framework for identifying, categorizing, qualifying and controlling DNA reactive (mutagenic) impurities to limit potential carcinogenic risk is provided in FDA and International Council for Harmonisation (ICH) guidance, M7(R1) Assessment and Control of DNA Reactive (Mutagenic) Impurities in Pharmaceuticals To Limit Potential Carcinogenic Risk (ICH M7(R1) Guidance). The ICH M7(R1) Guidance identifies nitrosamines as a structural group in the “cohort of concern” because of their classification as high-potency mutagenic carcinogens, though FDA acknowledges in the FRN that “[i]t is currently unknown if all or some NDSRIs are associated with this classification.” The ICH M7(R1) Guidance also describes the approach for the derivation of acceptable intake (AI) limits for certain chemicals that are considered mutagens and carcinogens. FDA notes that a computational toxicology assessment should be conducted using two quantitative structure-activity relationship ((Q)SAR) methodologies that can predict the outcome of a bacterial mutagenicity test.

FDA typically requests that applicants assess potential impurities for mutagenicity by conducting a standard in vitro bacterial reverse mutation test (the Ames test). If the Ames test is negative for a nitrosamine impurity, FDA has been requesting further testing because standard methods may not be adequate to characterize the mutagenic potential of nitrosamines. However, the FRN announces that “FDA’s National Center for Toxicological Research has been testing different conditions to develop an enhanced Ames test that is intended to provide a more reliable assessment of potential mutagenicity in small molecule nitrosamine impurities and NDSRIs.” Further, “[t]o avoid potentially duplicative nonclinical in vitro or in vivo testing of NDSRIs by manufacturers of drug products containing the drug substance, FDA is interested in exploring the feasibility of collaborative efforts among applicants and manufacturers of affected drug products.” The enhanced Ames test and collaborative efforts have the potential to reduce the testing burden on applicants. 

The FRN discusses the use of computational technology for predicting and classifying the biological activities of untested chemicals, focusing in particular on the uses and potential limitations of (Q)SAR models in the nitrosamine space. Given these limitations, the Agency notes that it “has been working with model developers and stakeholders to advance predictive toxicology, with a focus on the use of (Q)SAR methodologies in assessing potential mutagenicity and carcinogenicity of NDSRIs.” The Agency further explains that it and applicants have been using (Q)SAR methods to identify data-rich surrogates for data-poor NDSRIs “[i]f mutagenic potential is identified through toxicological testing or computational toxicology models.” In conducting this read-across, FDA notes that “[t]he nitrosamine structural alert environment is an important factor when selecting appropriate reference compounds for a read-across analysis” and the Agency provides that this assessment “may include consideration of the degree of substitution, steric bulk, electronic influences, potential for metabolic activation, stability/reactivity of the resulting metabolites, and overall molecular weight.” FDA also acknowledges the variability in quality of published carcinogenicity studies and notes that “use of less robust data can sometimes be considered acceptable when no more complete data exist, given the highly conservative nature of the risk assessment.” This discussion suggests that FDA is receptive to use of (Q)SAR models to identify surrogates, various considerations to selecting an appropriate surrogate nitrosamine for read-across, and less robust data to calculate an AI for NDSRIs.

FDA’s Ongoing Work on Nitrosamine Risk Assessment and Mitigation

FDA explains that it has continued to work to understand the root causes of nitrosamines and develop mitigation strategies for the presence of nitrosamines. In line with this work, FDA has published two examples of mitigation strategies related to formulation design on its website. The first was derived from reports that “commonly used antioxidants, such as ascorbic acid (vitamin C) or alpha-tocopherol (vitamin E), inhibit the formation of nitrosamines in vivo, based on data from human gastric fluid in vitro studies.” The second was “based on the fact that the formation of nitrosamines typically occurs under acidic conditions, whereas, in a neutral or basic environment, the kinetics of these reactions are significantly reduced.” Incorporating anitoxidants and excipients that keep the pH neutral or basic are strategies that applicants should consider employing to mitigate the risk of nitrosamine formation.

Regulatory Challenges

In discussing regulatory challenges associated with the call to review, the Agency notes the complexities associated with new drug application (NDA) and abbreviated NDA (ANDA) holders simultaneously evaluating their products for nitrosamines. FDA further explains that the Agency may be limited in the information that it can disclose about drug product impurities, as such disclosures may reveal aspects of an applicant’s manufacturing method or process (information that is generally protected from public disclosure) or information in other applicants’ submissions to FDA. This may, for example, result in circumstances “in which potential constraints regarding disclosure could hamper FDA’s ability to quickly and publicly identify a compound-specific recommended AI limit for an NDSRI that may be applicable to all drug products that contain the [active pharmaceutical ingredient].” In order to avoid these potential issues, FDA at times “generates and makes publicly available information or research to support the development of recommended AI limits by conducting additional studies, developing enhanced Ames testing, or using (Q)SAR methodology to identify appropriate surrogates from which read-across can be used to estimate carcinogenic potency.” Such efforts have the potential to reduce potentially duplicative studies, including in vivo animal studies that FDA generally seeks to replace, reduce, and refine (the 3R principles), where possible.

Collaborative Efforts To Develop NDSRI Data

FDA describes its role collaborating with applicants, stakeholders, other regulators, multi-laboratory projects, and model developers and stakeholders to advance predictive toxicology over the course of the investigation into nitrosamine impurities. For example, FDA mentions its collaboration on multi-laboratory projects being organized by the Health and Environmental Sciences Institute’s Genetic Toxicology Technical Committee (HESI GTTC). FDA separately announced on its website an FDA/HESI workshop on nitrosamine impurities in drugs scheduled for May 31 and June 1, 2023. In the FRN, the Agency also identifies the development of laboratory test methods to identify NDSRIs as an area that could benefit from collaboration. Furthermore, the Agency encourages applicants to publish scientific research and test results to further scientific knowledge on NDSRIs and facilitate regulatory decision-making.

Issues for Consideration and Request for Comments

At the end of the FRN, FDA identifies a number of questions about which it is requesting comment from the public regarding the identification, assessment, and control of NDSRIs in drug product development and regulatory review. The questions relate to the nitrosamine investigation generally, NDSRI risk assessments, collaborative efforts to develop NDSRI data, the establishment and implementation of AI limits, and access to medications. The Agency is also interested in any challenges preventing industry from engaging in this work. The FRN notes that the questions posed are not meant to be exhaustive and that FDA is interested in other pertinent information stakeholders would like to provide regarding relevant issues and challenges.