|Year : 2021 | Volume
| Issue : 2 | Page : 120-127
Nitrosodimethylamine impurities in metformin drug products: Physician insight
Chetan Doshi, Rajkumar Malayandi, Gajanan Namjoshi, Pramod Kadam, Dhananjay Mule
Department of Clinical Research, Research and Development, USV Private Ltd, Mumbai, Maharashtra, India
|Date of Submission||07-Jul-2020|
|Date of Decision||14-Aug-2020|
|Date of Acceptance||17-Sep-2020|
|Date of Web Publication||31-Mar-2021|
Dr. Chetan Doshi
USV Private Ltd, Arvind Vithal Gandhi Chowk, BSD Marg, Govandi, Mumbai 400088, Maharashtra.
Source of Support: None, Conflict of Interest: None
Metformin is a high-dose antidiabetic drug and most widely used first-line therapeutic agent for the management of type 2 diabetes mellitus (T2DM). Medicines regulatory agencies discovered contamination of genotoxic nitrosamine impurity in certain medications containing angiotensin receptor blocking (ARB) agents. This resulted in screening for nitrosamine impurities in a number of probable drug products. In November 2019, the Singapore government withdrew metformin drug products, due to the contamination of nitrosamine impurity, called nitrosodimethylamine (NDMA). The regulatory agencies from different geographies started investigation and subsequently, many products withdrew from the international market due to the presence of an unacceptable limit of NDMA in metformin tablets. Both pharmaceutical companies and regulatory agencies responded to mitigate this emerging issue. USV Private Limited (USV) has adopted a proactive quality risk management program to investigate the presence of genotoxic impurities in metformin products. The presence of NDMA impurities were tested in 425 batches of drug substances and drug products. Threshold toxicological concern (TTC) of all the batches was found to be ≤30 ng/day, when compared to the regulatory limit of 96 ng/day. Hence, USV metformin products are safe and can be continuously prescribed for the management of T2DM.
Keywords: Genotoxic, impurity, metformin, nitrosamine, regulatory, USV
|How to cite this article:|
Doshi C, Malayandi R, Namjoshi G, Kadam P, Mule D. Nitrosodimethylamine impurities in metformin drug products: Physician insight. J Diabetol 2021;12:120-7
| Introduction|| |
Metformin is one of the most widely used drugs in the treatment of type 2 diabetes mellitus (T2DM). Metformin got approval by UK regulatory agency (i.e., European Medicines Evaluation Agency [EMEA]) in 1958. Almost after four decades of clinical experience in Europe, it received approval by the United States Food and Drug Administration (USFDA) in 1995. According to the American Diabetes Association/European Association for Study of Diabetes guidelines, metformin is a first-line therapy for patients with T2DM. Over 50 years of rich clinical experience and research demonstrates the numerous clinical benefits of metformin such as anticancer, antiaging, cardiovascular protective, and neuroprotective properties. Moreover, it is used as an optional drug for polycystic ovary disease (PCOD). Metformin is a safe drug and has few minor adverse drug reactions (ADRs) such as nausea and vomiting. The most serious ADR of metformin is lactic acidosis; however, this ADR is rare (1 in 30,000), and mainly in patients of diabetes with kidney and liver dysfunctions.
The presence of trace amount of genotoxic impurities in pharmaceutical products is of increasing concern to both pharmaceutical industries and regulatory agencies due to their possibility for human carcinogenesis. Nitrosamine impurities are genotoxic in nature and can be present in a number of drug substances and drug products, and many such products are recalled from market by pharmaceutical companies as well as regulatory agencies. The regulatory agencies across the world have released regular updates into their investigations of drug products’ contamination with nitrosamines. Medicine regulatory authorities first became aware of the presence of the nitrosamine impurity nitrosodimethylamine (NDMA), in products containing valsartan in July 2018. In September 2019, USFDA announced some ranitidine medicines containing NDMA impurity at low levels, and subsequently, in April 2020, USFDA requested all manufacturers to withdraw all prescription and over-the-counter (OTC) ranitidine drugs from the market immediately. This impurity in some ranitidine products increases over time, especially when stored at higher than room temperatures. Owing to rising impurity upon shelf life, consumer exposure is increased to unacceptable levels of this impurity. Hence, all ranitidine drug products were withdrawn from market place.
In December 2019, the USFDA announced the presence of NDMA in some metformin products in other countries. The agency immediately began testing of NDMA in the metformin drug products, especially products that are being marketed in United States. FDA recommended five companies to voluntary recall of the extended release metformin because the agency’s testing showed NDMA above the acceptable intake limit in certain lots. Metformin is a high-dose drug and is prescribed widely, hence this review focuses on brief scientific and regulatory outline of NDMA impurities and product quality of metformin manufactured by USV, Mumbai, India.
| Methods|| |
The literature review was conducted using the web databases such as PubMed, MEDLINE, Web of Science, and Google Scholar. The systematic search of relevant regulatory guidelines, original research articles, reviews, and other public information such as press release from regulatory authorities, pharmaceutical companies, and other agencies was carried out till August, 2020. English is used as a language of search with keywords such as metformin, genotoxicity, impurities, NDMA, carcinogenicity, drug products, drug substances, regulatory, and nitrosamines. Reference lists of original articles and reviews were also searched manually. This review also consists of manufacturing and analytical data of metformin drug substances and drug products at USV’s manufacturing site (data on file).
Genotoxic impurities and regulations
The major goal of pharmaceutical development and manufacturing is to achieve high quality of the products, which are safe and efficacious. The presence of impurities in drug substances and drug products impacts the safety, efficacy, and quality of the drug substances/products. Historically, various drug regulatory authorities have issued guidelines to assess, limit, and control the ordinary impurities. Moreover, highly sensitive analytical procedures for quantifying the ordinary impurities in drug substances/products are well established. In the past few years, assessment and control of genotoxic impurities in pharmaceuticals gained more importance in both the scientific and regulatory community because of the carcinogenic potential of these genotoxic impurities. The sources of genotoxic impurities present in pharmaceutical products are starting materials, reagents, reaction by-products, and intermediates. The aim of the process chemistry is to explore the possible opportunities to avoid use and generation of these genotoxic impurities. Hence, quantifying and controlling these impurities is very important for establishing drug product safety and clinical acceptability. However, quantification of trace levels of genotoxic impurities using highly sensitive and selective analytical methodologies put tremendous challenges in front of the analytical community in pharmaceutical research and development.
Genotoxic compounds are the agents that interact with deoxyribonucleic acid (DNA) and/or cellular compounds or enzymes. Genotoxic compounds induce the mutation and/or chromosomal rearrangement, thereby act as carcinogens. The mechanism for causing damage to DNA include alkylation and/or covalent interaction, which may result in mutation of genetic code. Genotoxic compounds induce all types of DNA damage, whereas mutagenic compounds act on gene or chromosomal level. The interaction of genotoxic compounds changes the integrity or expression of genomic DNA, which leads to cancer. Guidelines of genotoxic impurities issued by different agencies such as USFDA, EMA, and ICH are public literature.,,,,,,
The intake of any unstudied compound that poses negligible risk of carcinogenicity is based on the acceptable threshold toxicological concern (TTC). Calculation of TTC is based on a very conservative approach that involves a simple linear extrapolation from the dose giving a 50% tumor incidence (TD50) to a 1 in 106 incidence, using TD50 data for the most sensitive species and most sensitive site of tumor induction.[Figure 1] shows the classification of genotoxic compounds and regulatory decision tree. Metformin is used as a chronic therapeutic agent (administered more than 10 years), a TTC-based acceptable intake of a mutagenic impurity of 1.5 µg per person per day, is considered to be associated with a negligible risk (theoretical excess cancer risk of <1 in 10000 over a lifetime exposure). [Table 1] summarizes the acceptable intakes for an individual impurity.
|Figure 1: Classification of genotoxic impurities and regulator decision tree|
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|Table 1: Acceptable intake for individual impurities based on duration of treatment|
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Strategies for control of genotoxic impurities
Genotoxic impurities can be identified using different methods such as (1) already known genotoxins, (2) possessing a similar function group of known genotoxic compounds, (3) in vitro genotoxic assays, and (4) in silico assessment by one of the many structure-based predictive software programs. The main focus of risk assessment is to identify the possible synthetic route and starting material, which results in residual genotoxic impurity during drug substance development and manufacturing. The alternative active pharmaceutical substances (API), synthetic strategies, or reagent should be explored to avoid genotoxic impurities. However, in some cases, it is difficult and/or practically impossible to adopt alternative strategies due to the complexity involved in drug synthesis. Hence, the additional end-stage purification techniques could be adopted to remove and/or control the genotoxic impurities in drug substances. But in few cases, genotoxic impurity is formed after synthesis due to degradation, interactions with containers, closures, and excipients (in case of drug product). It is mandatory to measure and monitor the genotoxic impurity during the initial release and stability to ensure the safety and quality of drug substances as well as drug products.[Figure 2] shows the strategies to control the genotoxic impurities.
The strategies for the control of genotoxic impurity in pharmaceutical products are as follows:
Redesigning the drug substance synthesis to avoid introducing problematic impurities
Altering relevant process parameters to remove or reduce such impurities to insignificant levels
Deploying process understanding to prove that a particular genotoxic impurity either cannot be formed or will be efficiently removed
Conducting toxicity studies to demonstrate that a suspect impurity is not harmful at the low levels envisaged for it
Classification of chemical carcinogens
Chemical carcinogens are compounds that can cause cancer in humans and experimental animals. Hundreds of chemicals are known to be carcinogenic/tumorigenic in animals. A carcinogen is termed genotoxic if it covalently binds to cellular DNA. If unrepaired, the damaged DNA may cause mutations by inducing the misincorporation of bases during DNA replication. Genotoxic carcinogens may either be direct acting (ultimately reactive toward DNA from the outset) or require metabolic activation to become reactive toward DNA (indirect-acting carcinogens). Mutagenicity refers to the permanent transmissible variations in the amount and structure of genetic materials of cells or organisms that can increase the frequency of mutations. Therefore, genotoxicity encompasses mutagenicity, but not all genotoxic substances are mutagenic, as they may not cause genetic alterations in DNA sequences. Epigenetic carcinogens are non-genotoxic, non-apoptotic, and noncytotoxic to the cell may still contribute to carcinogenesis in an epigenetic manner. Epigenetic carcinogens are carcinogens that do not damage DNA directly; however, they may enhance tumorigenesis by a variety of mechanisms. Epigenetic carcinogens may induce the generation of activating enzymes that metabolize carcinogens to DNA-reactive forms or may inhibit beneficial detoxifying reactions that convert procarcinogens to excretable forms that are not DNA reactive. Epigenetic carcinogens may also inhibit the repair of damaged DNA or serve as promoters. Promoters are agents that are not directly reactive toward DNA or mutagenic but instead they stimulate the growth and division of cells that may have already sustained the genetic damage that predisposes them to become tumorigenic. For example, arsenic, an established human carcinogen, does not initiate mutagenic damage but rather contributes to carcinogenesis by increasing reactive oxygen species (ROS) production, especially in pulmonary tissue, resulted in altered gene expression due to oxidative damage.
The International Agency for Research on Cancer (IARC) Monographs Programme identifies the causes of human cancer. IARC classification is based on the systematic assembly, review, and integration of evidence of human cancer, cancer in experimental animals, and cancer mechanisms. IARC evaluations are used worldwide by national and international health agencies to support a wide range of subsequent activities ranging from research to risk assessment, to preventative actions.[Table 2] summarizes the list of carcinogens based on IARC classification.
|Table 2: Group of carcinogens based on the International Agency for Research on Cancer classification|
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Nitrosamines are also called N-nitrosamines, a group of molecules containing the nitroso functional group. The formation of nitrosamines is generally only possible when secondary or tertiary amines react with nitrous acid. Nitrous acid itself is unstable but can be formed in situ from nitrites (NO2) under acidic conditions. Nitrosamines are carcinogenic impurities, and these impurities are rarely present in the pharmaceutical products. They are known mutagenic carcinogens, and the presence of nitrosamines in pharmaceuticals above acceptable limits is considered to produce carcinogenic effects on the human body. The probable root causes for the contamination of nitrosamines in pharmaceutical drug product are the use of nitrosating agent, use of contaminated reagents, solvents, starting material and intermediates in API synthesis, cross contamination in API manufacturing line, degradation of starting materials, intermediate and drug substances, and use of certain packaging materials. The list of nitrosamines along with corresponding amines are tabulated in [Table 3].
|Table 3: Different nitrosamines with their respective amine functionality|
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N-nitrosodimethylamine, known as NDMA, is nitrosamine impurity and classified as a probable human carcinogen based on results from laboratory animal tests and is listed under WHO/IARC group 2A and EPA group B2. [Figure 3] presents the structure of NDMA. The allowable daily intake for NDMA is 96 ng/day, whereas 26.5 ng/day for nitrosodiethylamine (NDEA). In the recent past, NDMA impurity gained importance in pharmaceutical product development scientists and regulatory professionals because of the presence of NDMA in marketed drug products containing sartans, ranitidine, and metformin, especially FDA announcement on recall of valsartan tablets in 2018. The unacceptable level of impurity is due to the use of sodium azide to improve the yield of the manufacturing process, whereas excessive amount of sodium nitrile was used to remove the sodium azide, which undergoes formation of nitrous acid under acidic conditions. The formed nitrous acid reacts with a small amount of dimethylamine to produce NDMA. Hence, all theoretically possible synthetic methodologies were mechanistically screened for possible formation of NDMA during drug substance synthesis and shelf. Marketed metformin drug products were analyzed in FDA laboratories, and it was found that there was the presence of NDMA impurities in metformin-extended release tablets manufactured by few generic companies.
Nitrosodimethylamine in daily consumed products
NDMA has been found in air, water, foods, cosmetics, tobacco, and packing materials. NDMA is virtually present in all food items, including but not restricted to snacks, beverages, fruits, vegetables, vegetable oils, milk, milk products, sea foods, meat, processed meat, salads, and seasoning. Apart from food and beverages, NDMA is also present in toilet preparations, disinfectants, cosmetic formulations, shampoos, and soaps. The human exposure of NDMA occurs through different routes such as oral, skin, and inhalation. However, oral route is the predominant route for human exposure to NDMA, due to ingestion of contaminated foods and beverages. Nitrile compounds are used as a preservative to prevent the growth of Clostridium botulinum in processed meats that facilitates the nitrosamine formation during the process. For this reason, high NDMA concentrations have been reported in processed meat such as bacon, sausage, and ham; however, a lower amount of NDMA is present in meats that did not go through processing. NDMA is also present in alcoholic beverages such as beer, wine, and whiskey. NDMA is also present in water, the disinfectant added during the recycling process of water interacts with residual amines and facilitates the formation of NDMA.
Metformin manufacturing process
USV’s manufacturing process for metformin is a single-step synthetic process. The critical material attributes and process parameters are designed to minimize and/or eliminate the nitrosamine impurities in final drug substances. [Figure 4] shows the schematic diagram of synthesis of metformin.
USV’s risk assessment strategy
The drug substances synthesis involves the use of reactive chemicals, reagents, solvents, catalysts, and other processing aids. It is virtually not possible to synthesize the drug substances without impurities. Impurities are formed during the synthesis and/or subsequent degradation of drug substances or by-products. Genotoxic impurities are uncommon in most of the drug substances, and synthesis of few chemical entities results in genotoxic impurity. As a special case, while synthesizing and purifying these compounds, the cognizant approach is mandatory from designing to manufacturing. Deploying appropriate quality risk management systems in research and manufacturing is essential for continuous manufacturing and supply of quality products, it is possible to identify, measure, and control the genotoxic impurities using appropriate risk mitigation strategies. The risk assessment strategies for genotoxic impurities should be assessed in different stages of product development such as process selection, process conditions, processing solvents, method of purification, stability, and storage conditions. The process chemists always try to explore the possible opportunities to avoid the use and generation of these genotoxic substances in the manufacturing process. However, the complete elimination/prevention of such impurities is always not achievable. Hence, appropriate mechanistic approach for the identification of root cause and factors influencing generation of impurities needs to be studied using well-defined statistical research methodologies. Modeling different variables and identifying the variates and covariates that are influencing the formation of impurities need to be investigated. Development of appropriate analytical methodology with high-level sensitivity, accuracy, precision, and reproducibility is the prerequisite for optimal quality risk management, which offer consistently high-quality products.
The USV’s risk assessment consists of the following quality elements, as follows:
Route of synthesis of metformin
Route of synthesis of starting materials and reagents
Use of highly sensitive analytical methods
Impurities in the starting materials
Solvents (including water, recovered or recycled)
Facilities and equipment used
Process monitoring and data analytics
USV’s metformin drug substance consists of stringent control of NMDA impurity level. NDMA TTC level of USV’s metformin is 32 ng/day, considering the highest total daily dose of metformin present in pharmaceutical dosage forms.
Food and Drug Administration’s recall
The possibly genotoxic impurities, especially nitrosamines have been found in several drug products of angiotensin II receptor blocking agents. Later, similar impurity contamination was found with ranitidine, an anti-ulcer drug sold as OTC medicine and prescription drug. These drugs were withdrawn from the marketplace not only in the United States but also in the global market. Since then, most of the regulatory agencies have been investigating the presence of nitrosamine impurities in certain drug products. The global investigation for nitrosamine impurities in pharmaceuticals was further extended to metformin-extended release tablets, after the Singapore government revealed that it had recalled three of 46 metformin medicines on the market due to the presence of NDMA impurity. The investigation was conducted by USFDA and EMA to determine whether metformin medicines of respective countries contain NDMA impurity and whether it is above the acceptable daily intake limit of 96 ng/day. The outcome of the investigation resulted with voluntary recall of metformin-extended release tablets from five different companies.
Valisure, a first American analytical pharmacy, has tested and detected high levels of NDMA (>96 ng/day) in metformin formulations and filed citizen petitions. Some of the marketed batches of metformin-extended release 500 mg tablets contain 16.5 times higher concentration of NDMA impurity than TTC level of 96 ng/day. FDA petition requests FDA commissioner to conduct examinations and investigation under Section 702 (a) of the FDCA (21 U.S.C. § 372(a)) regarding these products, their manufacturing processes, and the manufacturer submissions made for FDA approval under 704 (a) of the FDCA (21 U.S.C. § 374(a)), and effect labeling revisions as needed.
USV’s metformin drug product quality
USV has adopted a proactive approach, and the entire basket of both drug substances and drug products of USV’s metformin across the market geographies has been investigated for quantifying the NDMA impurity. More than 425 batches (>125 batches for drug substance, >150 batches of Glycomet IR, >150 batches of Glycomet SR) of different bins were analyzed using a validated analytical methodology to estimate NDMA levels. The results of quality risk management program reveal that the NDMA levels were found to be less than 30 ng/day for metformin drug substance and drug products. [Table 4] presents the summary of NDMA investigation on USV’s metformin products. Further, the results confirm that NDMA levels are similar for both drug substances and drug products, and moreover, it was observed that there is no rise in impurities level upon stability.
|Table 4: Summary of nitrosodimethylamine investigation on USV’s metformin products|
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| Conclusion|| |
Nitrosamine impurities are a rising concern for pharmaceutical companies as well as regulatory agencies, not only for retrospectively analyzed drug substances and drug products, which are already approved and available in market, but also for new approvals. NDMA is one of the most frequently reported nitrosamine impurities in a handful of drug substances and drug products. Metformin, being an important medicine for diabetic care, is consumed by a large number of patient populations with high dose; pharmaceutical industries as well as regulatory agencies responded quickly to address the quality concerns. Many pharmaceutical companies including USV adopted very sensitive and selective analytical methodologies recommended by agencies to quantify the NDMA impurity, using advanced analytical tools, which facilitated quality risk assessment of the batches manufactured. Although NDMA is exposed to humans in day-to-day life from food products, beverages, cosmetics, and personal care products, it is mandatory to control the exposure of NDMA from pharmaceuticals. As a part of continuous quality risk assessment program, USV proactively analyzed large number of metformin drug substances and drug product batches. The results show that NDMA TTC levels are one-third times lower (i.e., 30 ng/day) than regulatory limit of 96 ng/day. Hence, USV metformin products are safe and can be continuously prescribed for the management of T2DM.
Financial support and sponsorship
This study was supported by USV, Mumbai, Maharashtra, India.
Conflicts of interest
There are conflicts of interest. All the authors are currently employed at research and development function of USV, Mumbai, Maharashtra, India.
| References|| |
Scarpello JH, Howlett HC Metformin therapy and clinical uses. Diab Vasc Dis Res 2008;5:157-67.
Inzucchi SE, Bergenstal RM, Buse JB, Diamant M, Ferrannini E, Nauck M, et al
. Management of hyperglycaemia in type 2 diabetes: A patient-centered approach. Position statement of the American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASD). Diabetologia 2012;55:1577-96.
Wang YW, He SJ, Feng X, Cheng J, Luo YT, Tian L, et al
. Metformin: A review of its potential indications. Drug Des Devel Ther 2017;11:2421-9.
European Medicines Agency. The tripartite harmonised ICH Guideline S2 (R1): Guidance on genotoxicity testing and data interpretation for pharmaceuticals intended for human use. 2012. Available from: https://www.ema.europa.eu/en/documents/scientific-guideline/ich-guideline-s2-r1-genotoxicity-testing-data-interpretation-pharmaceuticals-intended-human-use-step_en.pdf. [Last accessed on 2020 Jun 29].
USFDA. FDA updates table of interim limits for nitrosamine impurities in ARBs. 2019. Available from: https://www.fda.gov/drugs/drug-safety-and-availability/fda-updates-and-press-announcements-angiotensin-ii-receptor-blocker-arb-recalls-valsartan-losartan. [Last accessed on 2020 Jun 29].
USFDA. FDA announces voluntary recall of Sandoz ranitidine capsules following detection of an impurity. 2019. Available from: https://www.fda.gov/news-events/press-announcements/fda-announces-voluntary-recall-sandoz-ranitidine-capsules-following-detection-impurity. [Last accessed on 2020 Jun 29].
Woodcock J Statement from Janet Woodcock, M.D., director of FDA’s Center for Drug Evaluation and Research, on impurities found in diabetes drugs outside the U.S. 2019. Available from: https://www.fda.gov/news-events/press-announcements/statement-janet-woodcock-md-director-fdas-center-drug-evaluation-and-research-impurities-found. [Last accessed on 2020 Jun 30].
USFDA. FDA names companies recalling ER metformin. 2020. Available from: https://www.fda.gov/drugs/drug-safety-and-availability/fda-updates-and-press-announcements-ndma-metformin. [Last accessed on 2020 Jun 30].
Linda KD, Marvin MH, Brain WP, Todd JP, Steven WB The assessment of impurities for genotoxic potential and subsequent control in drug substances and drug products. J Pharm Sci 2013;102:1404-18.
Gyorgy S, Miriam C, Amores DS, Marco G, Frederico CF, William H Genotoxic impurities in pharmaceutical manufacturing: Sources, regulations, and mitigation. Chem Rev 2015;115:8182-229.
David EM, Mark H, Robert RM Carcinogenesis: Mechanisms and manifestations. In Wanda H, Colin R, Matthew W, editors. Hascheck and Rousseanx’s Handbook of Toxicological Pathology. 3rd ed. Amsterdam, Netherlands: Academic Press; 2013. p. 107-46.
Sabine ASL, Gudrun K, Daniel D, Fahd AM, Rabeah AT, Amedeo A, et al
. Causes of genomic instability: The effect of low dose chemical exposure in modern society. Carcinogenesis 2015;36:61-88.
USFDA. Genotoxicity Testing and Data Interpretation for Pharmaceuticals Intended for Human Use. 2012. Available from: https://www.fda.gov/media/71980/download. [Last accessed on 2020 Jun 30].
European Medicines Agency. Assessment and Control of DNA Reactive (Mutagenic) Impurities in Pharmaceuticals to Limit Potential Carcinogenic Risk, 2010. Available from: https://www.ema.europa.eu/en/ich-m7-assessment-control-dna-reactive-mutagenic-impurities-pharmaceuticals-limit-potential. [Last accessed on 2020 Jun 30].
European Medicines Agency. Guideline on the limits of genotoxic impurities, drafts released for consultation in 2002 and 2004, final version released in 2006, CPMP/SWP/5199/02, EMEA/CHMP/QWP/2513442006; Committee for Medicinal Products (CHMP). 2006. Available from: https://www.ema.europa.eu/en/documents/scientific-guideline/guideline-limits-genotoxic-impurities_en.pdf. [Last accessed on 2020 Jun 30].
European Medicines Agency. Questions and Answers on the Guideline on the Limits of Genotoxic Impurities, EMA, 2008 and 2009 (published as an official document in 2010:21. EMA/CHMP/ SWP/431994/2007 Rev. 3). 2012. Available from: https://www.ema.europa.eu/en/documents/scientific-guideline/questions-answers-guideline-limits-genotoxic-impurities_en.pdf. [Last accessed on 2020 Jul 01].
European Medicines Agency. Guideline on the Assessment of Genotoxicity of Herbal Substances/Preparations, 2008. Available from: https://www.ema.europa.eu/en/documents/scientific-guideline/guideline-assessment-genotoxicity-herbal-substances/preparations_en.pdf. [Last accessed on 2020 Jul 01].
USFDA. Guidance for Industry (Draft), Genotoxic and Carcinogenic Impurities in Drug Substances and Products: Recommended Approaches. 2008. Available from: http://www.triphasepharmasolutions.com/Resources/Guidance%20for%20Industry%20Genotoxic%20Agents.pdf. [Last accessed on 2020 Jul 01].
European Commission. Risk Assessment Methodologies and Approaches for Genotoxic and Carcinogenic Substances. 2009. Available from: https://ec.europa.eu/health/archive/ph_risk/committees/04_scher/docs/scher_o_113.pdf. [Last accessed on 2020 Jul 01].
Christian CA. Carcinogenic food contaminants. Cancer Invest 2007;25:189-96.
Derek IR Control of genotoxic impurities in active pharmaceutical ingredients: A review perspective. Org Process Res Dev 2010;14:946-59.
Paula AO, Aura C, Raquel C, Henrique GP, Luis FDP, Carlos L Chemical carcinogensis. Ana Acad Bras Cienc 2007;79:593-616.
Jessica LB, Maria Z, Kaarthik J, Miriam CP, Francis LM Carcinogens and DNA damage. Biochem Soc Trans 2018;46:1213-24.
Nicholas B, Mustafa AZ, Michael B, Robert AB, Jan Z, Daniel K Overview of biological mechanisms of human carcinogens. J Tox Env Heath Part B 2019;22:288-359.
WHO. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, 2010. Lyon, France: WHO. Available from: https://monographs.iarc.fr/wp-content/uploads/2018/06/mono99.pdf. [Last accessed on 2020 Jul 01].
Tom B, Micheal RT Nitrosamine formation from the oxidation of secondary amines. Water Sci Tech 2011;11:259-65.
Tabrez S, Amit G, Hussain S Nitrosamine impurities in drug substances and drug products. J Adv Pharm Pract 2020;2:48-57.
USFDA. FDA updates and press announcements on NDMA in Zantac (ranitidine). April 2020. Available from: https://www.fda.gov/drugs/drug-safety-and-availability/fda-updates-and-press-announcements-ndma-zantac-ranitidine. [Last accessed on 2020 Jul 02].
Maria KP, Jan FP NDMA impurity in valsartan and other pharmaceutical products: Analytical methods for the determination of N
-nitrosamines. J Pharm Biomed Ana 2019;164:536-49.
Jong-eun P, Jung-eun S, Jee-yeon L, Hoonjeong K Distribution of screen N-nitrosamines in food. Toxicol Res 2015;31:279-88.
Health Science Authority. HSA recalls three out of 46 metformin medicines, HAS updates (November, 2019). Available from: https://www.hsa.gov.sg/announcements/news/hsa-recalls-three-out-of-46-metformin-medicines. [Last accessed on 2020 Jul 02].
Valisure. Valisure citizen petition on metformin. March 2020. Available from: https://www.valisure.com/wp-content/uploads/Valisure-FDA-Citizen-Petition-on-Metformin-v3.9.pdf. [Last accessed on 2020 Jul 02].
[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3], [Table 4]