Contamination Drives a More Concerted Approach to Genotoxins

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Pharmaceutical Technology, Pharmaceutical Technology-05-02-2020, Volume 44, Issue 5
Pages: 46-49

Discovery of carcinogenic nitrosamines in three of the world’s most widely prescribed drugs is driving efforts to better detect, control and prevent their generation in APIs and finished drug products.

Since traces of the compounds were first found in batches of APIs used to make valsartan and other sartan ARBs in 2018, drug manufacturers have been paying much closer attention to nitrosamines -in particular NDMA (N-Nitrosodimethylamine)-and how they enter the pharmaceutical supply chain. “Nitrosamines are extremely carcinogenic, as academic researchers have known for decades. The fact that NDMA is used to this day as a control to induce cancer in rats just underscores its immense carcinogenic potential,” says David Light, CEO of Valisure, an analytical pharmacy that filed the first citizen’s petition on nitrosamine contamination in ranitidine with FDA.  

Some cases of contamination have been traced to solvents and to inadequate manufacturing and quality testing practices. In the case of the first contaminated API, for valsartan, one supplier had tweaked its synthesis process to improve yield and efficiency. Not only the manufacturer but the regulators who okayed that change failed to realize that it would result in contamination (1). 

But ARBs were only the first sign of trouble, and, for one drug (so far), the problems go much deeper than manufacturing and quality control.  In 2019, extensive testing found that ranitidine, one of the most widely prescribed treatments for ulcers and acid indigestion  (whether as the trade named Zantac or as one of many generic and over-the-counter brands), was also contaminated with NDMA. Valisure and Emery Pharma filed citizen’s petitions with FDA in 2019 and 2020. detailing the public health dangers posed by this contamination (2 - 4).  Although manufacturing and storage practices have led to contamination in some cases, the ranitidine molecule itself was found to be inherently unstable, breaking down and generating NDMA in the presence of high temperatures and humidity levels. After disputes about the best methods to use for analysis and testing (4), product recalls ensued, and on April 1, 2020 the US FDA followed other global regulatory agencies in banning the sale of ranitidine and products that contain the compound (5). This product had been on the market for almost 40 years and was widely prescribed to pregnant women and young children. 

In December 2019, news came from regulators in Singapore, and later, from Canadian and Swiss health authorities that NDMA and nitrosamines had also been found in metformin, the fourth most widely prescribed drug in the US, and one of the most widely prescribed diabetes treatments in the world. In March 2020, after testing 38 lots of metformin from 22 suppliers, Valisure filed a citizen’s petition with FDA (6).

Far from being isolated instances, nitrosamine contamination is a systemic issue that manufacturers of all types need to take seriously. Although more is being learned about how it occurs, there are still gaps in that knowledge, says Ron Najafi, CEO of Emery Pharma, which sent a citizen’s petition to FDA in January 2020 after studying ranitidine stability to identify the source of NDMA contamination. Emery is testing a number of other pharmaceuticals in an attempt to clarify the root causes of such contamination. The company has already developed and validated new analytical methods for such tests. 

New guidance from USP

The United States Pharmacopeial Convention (USP) will be releasing new guidance later in 2020 to help manufacturers better face, address, and prevent nitrosamine contamination problems for pharmaceuticals and APIs. Included will be an informational chapter, as well as a series of six reference standards that can be used as controls and in method validation, says Jaap Venema, chief scientific officer with USP. 

Venema believes that decisive action is required now, since the contaminant has been found in three very different types of products from very different sources.  Longer term, he believes that more work is needed in assessing the risk, not only of nitrosamines, but of other genotoxins. “We need to do more as a healthcare system, as a supply chain, to control, test and predict potential impurities,” he says.

Considering the first recent contamination case involving the valsartan API, initially there was a lot of finger pointing and blaming of the manufacturer, a Japanese company doing business in China, in media reports. In fact, Venema emphasizes that, although manufacturing facilities and processes were inspected, no one expected to find NDMA in that setting.  “If there is one lesson to be learned by all, it is to expect the unexpected…It all comes down to the need for more control, more testing, and more predictive work,” says Venema. 

Studying metformin

After other global regulatory agencies recalled metformin, FDA tested samples of the drug, examining material from 16 batches made by seven manufacturers.  The agency released data in February 2020 that found contamination levels below the limit, Light recalls.

Valisure decided to investigate metformin after a person sent Valisure a sample of the compound and said that she was concerned about its purity, Light says. Valisure’s lab found a very high level of NDMA in that sample, he says. Valisure then bought more metformin from distributors, analyzing 38 batches of the material from 22 companies. During testing, 16 of the batches failed. Half of the manufacturers had at least one batch that failed, while many had batches that contained more than ten times the legal limit of NDMA, Light says (7).

These results highlight some of the procedures that limit FDA, which, when it tests for contamination, must ask the industry for voluntary samples. “Manufacturers can generally choose what they send. We buy direct from distributors, rather than manufacturers, so we get material from the end of the supply chain,” he says. Light filed the Citizen’s Petition on March 2.  



Testing methods

There have been ongoing questions about the best analytical methods for detecting nitrosamines in pharmaceuticals. “I don’t think there will ever be a consensus among stakeholders as to a single set of ideal conditions or methods. Instead, I believe drugs should be tested by multiple complementary methods in an unbiased fashion, and the conditions/tests set on a case-by-case basis,” says Light.


As he notes, disagreements that ensued after NDMA detection in ranitidine using headspace GC-MS (‘HS-GC-MS’) have largely been resolved and it is now well-established that HS-GC-MS should not be the method for analysis of ranitidine. “As careful scientists looking at the problem as a whole, we developed our own low-temperature GCMS version to analyze ranitidine. We also thought the 15 min exposure to 130 º C had a dramatic effect on ranitidine.  As chemists, we saw that it was a very efficient reaction, to have a nearly 10 % molar conversion in 15 minutes of 130 º C exposure, most other drug molecules do fine under those conditions. Which is why that method had been the standard.

From a scientific perspective it doesn’t really matter what method you use as long as you address primary issues. We addressed molecule’s instability by using lower temperatures with GC-MS, FDA did the same for LC-MS.“There is a need to think a little bit outside of the box. You cannot wait for there to be a very specific prescribed system for the exact drug you’re looking at. If we had done that, rantidine would still be on the market around the world,” he says.

Emery has collaborated with Valisure on much of its work, and corroborated its test results.  The company explored use of alternative methods, including liquid chromatography (‘LC’) – tandem mass spectrometry (‘MS/MS’), which does not expose the samples to high temperatures.  Using this method, together with stability studies, Najafi and his team found that ranitidine is an unstable compound, a time-and temperature-sensitive pharmaceutical product, that breaks down to form NDMA.

“After nearly four decades in the market, we were the first to prove that ranitidine develops the carcinogen NDMA when exposed to heat, a common occurrence during transportation and storage,” says Najafi.  Therein lies the importance of Emery’s findings, he says, since temperature excursions are quite common during commercial pharmaceutical shipment.

Emery had a strong set of preliminary data (unpublished at this point) to support these claims, Nafaji says, when, on December 4, 2019, FDA offered a directive for manufacturers regarding ranitidine product release. The Agency said that distributors and manufacturers could release ranitidine drug products back into the market, so long as production batches showed NDMA levels lower than 96 ng/pill (the daily acceptable limit of NDMA). “We were extremely concerned, because no formal root-cause analyses had been performed to determine why NDMA was observed in several lots of Zantac and other ranitidine drug products,” says Najafi. 

“Even if manufacturing lots were clean, NDMA could still be produced in ranitidine drugs products during downstream shipment and storage, or if stored by patients under less-than-ideal conditions, e.g. in a car dashboard,” says Najafi. “We felt an obligation to inform the agency of our findings, given the major implications they had for public health,” he says, and filed a citizen’s petition with FDA in January 2020.

Existing regulations inadequate 

ICH M-7 is a comprehensive guidance for genotoxic compounds that has guided FDA’s approach to nitrosamine contaminants. Kristi Muldoon Jacobs, USP’s regulatory science director, likes the fact that it allows pharma to take advantage of advances in toxicology and collective knowledge, to help identify genotoxic impurities. 

However, there are some places where it could be improved or added to, she says. For example, when discussing known and suspected mutagens, some chemicals, for which there isn’t enough information (and which include nitrosamines) are labeled “cohorts of concern.” The guidance doesn’t give much information on how those compounds should be addressed, so the pharma community should add to the guidance as more is learned from specific cases, she says. For example, there is a list of chemicals for which acceptable daily intake (or ADI) levels have been published, and now that more information has been published on nitrosamines, it can be used to update the guidance, she says. 

Current FDA and USP guidance is reasonable, albeit a bit dated at this point, says Najafi.“Impurities are often better dealt with on a case-by-case basis, which is difficult to do with a broad guidance document,” he says. One problem that he sees is the bureaucratic red tape that surrounds updating these documents. “We need quicker, more facile updates to guidance documents and monographs, and analytical methods from 36 years ago should be updated with newer instrumentations and methodologies,” he says.  For examples, manufacturers could be required to perform unbiased assessment of impurities in every production lot, using multiple analytical methodologies (e.g., GC-MS, LC-MS, UV-Vis, NMR, or HPLC) instead of being allowed to pick and choose their favorite method., says Najafi, then they could pursue all new or unidentified peaks, identify the impurities/analytes responsible for these peak(s), and ensure these are within established safety profiles before releasing a product lot.  “On the other hand,” Muldoon Jacobs says, “standards ensure that the methods are fit for purpose and that everyone is using the same methods.  USP is currently working to update and providing additional chapters to provide risk-based approaches and suitable verifiable testing methods.”

Greater familiarity of and compliance with FDA, EMA, ICH, guidance is needed, Najafi says. “Regulators around the globe need to come down on non-compliance with an iron fist,” he adds. He points to the 2018 valsartan API contamination, when problems came up when manufacturers deviated from monographs and established procedures to improve process yield.  Generic pharmaceutical manufacturers, especially those offshore, should be required to stick with the monograph. “If a recipe calls for having a fly in the room, you need to have one there,” says Najafi.

During the new drug application (NDA) phase, CMC (chemistry, manufacturing and control) review is very tough, but generic pharmaceuticals don’t undergo that same level of scrutiny. If a generic drug manufacturer wants to make process changes, Najafi says, they should submit an application for re-approval to FDA, even if they’re only making a change as basic as switching solvents. “A contamination level of 96 ng per pill may not be a lot, in fact, it is less than 0.00001%, but NDMA is so significant a toxic compound that one should worry and have control over it,” says Najafi.



More rigorous testing

Manufacturers also need to do better on testing, particularly with residual solvent analysis, says Najafi, and manufacturers should be able to analyze, record, and report levels of each solvent. In reality, some manufacturers completely ignore these impurities, he says. “There is no reason to ignore them. We have amazing analytical instruments such as mass spectrometers to perform the analyses. If manufacturers argue that they can’t afford a GC-MS system, they shouldn’t be in business,” he says. 

Scientists working in other industries have been studying nitrosamine contamination since the 1970’s, says Light, but pharma and its regulators have often seemed disconnected from that research.  In addition, he says, there is a very large body of research on the potential risks of nitrosatable drugs (e.g., those containing secondary and tertiary amines, in which the building blocks of nitrosamine carcinogens are on the drugs themselves). A number of studies have examined nitrosatable drugs during pregnancy, and correlated use of the drugs with teratogenic effects, stillbirths, and tumors, says Light. 

“The pharmaceutical world has not kept up with other industries on the topic of nitrosamines, although it is getting better,” says Najafi. “There is a wealth of literature on the subject from scientists in the food processing and waste-water industries that we in the pharmaceutical world must continue to tap into,” he says.“Widespread cross-talk among scientist is the only way to bridge the existing knowledge gap, and government agencies and regulators should facilitate it,” says Najafi. Emery, for example, has started collaborating on studies of nitrosamine and other genotoxic impurities with Prof. Bill Mitch from Stanford University, a specialist in the field of environmental biomonitoring, public health, and emerging carcinogens.

In the meantime, the toxicological methods used to study nitrosamine impurities in pharma  continue to evolve. “I believe this area is still a black box - long-term exposure risk is and will remain challenging to evaluate,” says Najafi. “While working on ranitidine, we realized that there have been no clean epidemiological studies on this drug, even though ranitidine has been on the market for decades and has been taken by millions around the world! The same may be true for many more drugs,” he says. Valisure is working with Memorial Sloan Kettering Cancer Center on a study of ranitidine’s health effects, which underwent peer review and was scheduled to be published in January 2020 in the Journal of the American Medical Association, but which is being held for further review. Light expects the article to be published at some point this year.

The field of toxicology is advancing rapidly, adopting more predictive and in-vitro approaches, says Muldoon Jacobs. In the future, she expects predictive tools to be routinely pulled into manufacturing, to predict whether impurities may be present and to help determine their potential toxicity. 

Some computer-based predictive models, she says, can be used to predict whether a compound’s or contaminant’s given chemical structure might be mutagenic and whether or not it would test positive in the Ames assay (8), which has been used for over 25 years to identify mutagenic compounds. “These models are built on hundreds or thousands of individual data pieces based on actual studies, and some scientific papers have shown that these models are more accurate than the Ames test,” she says.  Pharmaceutical industry regulatory agencies are evaluating and applying these methods, for instance, at FDA’s Division of Applied Regulatory Science, she says.

Although mass spec and hyphenated gas and liquid chromatography methods are being used to detect nitrosamines in the pharmaceutical supply chain, new analytical methods may be applied in the future.  The UK-based company, Ellutia, for instance, offers TEA detector technology which uses chemiluminescence at the GC or LC interface, to measure levels of N-nitrosamines. A Total analyzer is available that gives one cumulative measurement of all nitrosamine contaminants in four minutes. The detector is widely used in Europe in the rubber toy, brewing, water treatment and food industries, but pharmaceutical companies have just begun to explore its potential. 

The industry is taking the issue of nitrosamine contamination and its potential human health impacts more seriously. “As with the current COVID-19 pandemic, it’s not a matter of if, but when, situations like this will come up. Nitrosamines are very much on our minds right now, but history has taught us there will be other cases involving other genotoxic contaminants in the future. The questions for the industry now are: How do we prevent more of these situations from occurring (knowing there won’t be a preventive method that is 100% fail-safe)? How do we prepare for them, and how do we respond faster and more responsibly when they recur?  The real lesson for our industry is to get better at predicting and preventing these problems,” says Venema.


1. A. Shanley, PharmTech 42 (10), pp. 60-64 (2018).
2. Valisure, Citizen’s Petition to FDA, valisure. com, September 9, 2019
3. Emery Pharma, Citizen’s Petition to FDA,, January 2, 2020.
4. A. Shanley, “Problems With Ranitidine May Transcend Manufacturing Issues,”, October 2, 2019.
5. FDA News Release, “FDA Requests Removal of All Ranitidine Products From the Market,”, April 1, 2020.
6. FDA, Statement from Janet Woodcock on Nitrosamine Impurities Found in Diabetes Drugs Outside the US,, December 5, 2019.
7. Valisure, Citizen’s Petition to FDA on Metformin, March 2, 2020,
8. R. Luhana, “Online Pharmacy Valisure Discovers Carcinogen in Some Batches of Metformin,” newyork.legamexaminer. com, March 18, 2020.
9. ICH M7(R1), Assessment and Control of DNA-Reactive (Mutagenic) Impurities in Pharmaceuticals, www.database.ich. org, March 31, 2017.
10. C. Landry et al, Regulatory Toxicology and Pharmacology 109 (12), December 2019.

Article details

Pharmaceutical Technology
Vol. 44, No. 5
May 2020
Pages: 46-49


When referring to this article, please cite it as A. Shanley, "Contamination Drives a More Concerted Approach to Genotoxins," PharmTech 44 (5) 2020.