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Higher-than-acceptable levels of the nitrosamine impurity N-nitrosodimethylamine (NDMA) were detected in certain metformin products used to treat type 2 diabetes, the on Thursday.

NDMA, a genotoxic substance and known carcinogen, is often found in contaminated water or cured and grilled foods. Although everyone is exposed to some level of NDMA, the FDA caps the acceptable daily intake limit at 96 ng. The agency set that level in 2018 when NDMA was discovered in some cardiovascular medications, determining from a variety of data sources that 96 ng/day for 70 years would result in a one in 100,000 cancer risk.

As a result, the agency contacted five manufacturing firms to recommend a voluntary recall of the extended-release formulation of metformin. So far, is the only firm to do so, issuing a voluntary recall on Wednesday of all of the company's lots of 500-mg metformin hydrochloride extended-release tablets.

However, the FDA emphasized that many other extended-release metformin products are available that do not appear to have excessive NDMA, comprising a "significant portion of the U.S. market," and these are not being recalled.

The FDA said it is working with manufacturers to ensure appropriate testing of these products and is working to prevent any subsequent metformin shortages that will come as a result of the recalls.

Metformin contamination with NDMA isn't a new issue. This announcement comes on the heels of a prior in December 2019 advising that low levels of NDMA were found in some metformin formulas in other countries. Following this up with its own investigation, the agency later had identified trace levels of NDMA in metformin products sold in the U.S. in February 2020. But because no samples exceeded the acceptable daily limit of 96 ng, the agency did not recommend metformin recalls at the time.

"The FDA has strict standards for safety, effectiveness, and quality, and the agency makes every effort based on science and data to help keep the U.S. drug supply safe," said Patrizia Cavazzoni, MD, acting director of the FDA's Center for Drug Evaluation and Research, in a statement. "We understand that patients may have concerns about possible impurities in their medicines, and want to assure the public that we have been looking closely at this problem over many months in order to provide patients and health care professionals with clear and accurate answers."

"Now that we have identified some metformin products that do not meet our standards, we're taking action," she added. "As we have been doing since this impurity was first identified, we will communicate as new scientific information becomes available and will take further action, if appropriate."

Despite the recommendation for voluntary recalls, the FDA said all patients should continue taking their current metformin medication and should follow up with their healthcare provider to be prescribed a replacement medication.

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