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Global health regulators are looking into whether widely used diabetes drugs may contain unsafe levels of a carcinogen that has previously been found in heart and gastric medications.

The U.S. Food and Drug Administration said in a statement Wednesday that the agency is testing samples of metformin sold in the U.S. for NDMA, and that it will recommend recalls of the medication as appropriate. Metformin is widely prescribed to patients when they are initially treated for type 2 diabetes.

“The agency is in the beginning stages of testing metformin,” said FDA spokesman Jeremy Kahn in an emailed statement. “However, the agency has not confirmed if NDMA in metformin is above the acceptable daily intake (ADI) limit of 96 nanograms in the U.S.”

Kahn said diabetes is a serious condition and patients who take metformin shouldn’t stop taking their medication without first talking to their doctors.

Earlier Wednesday, the the European Medicines Agency said companies should test for high levels of NDMA in metformin. No dangerous levels have been detected in EU supplies to date, and patients should continue taking their diabetes treatments as prescribed, the agency said in an emailed response to questions.

Metformin is made globally by numerous generic drugmakers. NDMA is known to cause cancer in animals and is classified as a possible human carcinogen.

“Although the risk from NDMA seen so far has been very low, impurities such as NDMA should be avoided in medicines,” the EMA said in the email. “If NDMA is found above a certain level, authorities will take necessary action.”

Concerns about high levels of NDMA, which can form during some industrial processes, have been rising since it was found in blood-pressure medications and drugs containing ranitidine, the active ingredient in Sanofi’s Zantac for heartburn.

Poland’s health minister, Lukasz Szumowski, said earlier that officials were scrutinizing metformin-containing drugs but that no products would be pulled from the market as NDMA had been found in only trace amounts. He urged patients to continue taking their medications, as the benefit of diabetes treatment outweighed any theoretical cancer risk.

Singapore health officials recalled three of 46 versions of metformin marketed there after finding NDMA amounts “above the acceptable level.” The recalled drugs had been sold locally for only a short time, and the risk to patients who had taken them is low, Singapore’s Health Sciences Authority said in a statement.

The EMA also advised patients to change their treatment only with the advice of a doctor. Metformin is the active substance in Bristol-Myers Squibb Co.’s Glucophage, Sandoz’s Etform, Teva Pharmaceutical Industries Ltd.’s Metformax and Berlin-Chemie AG’s Siofor.

Novartis AG’s Sandoz unit recalled generic prescription ranitidine in the U.S. in September after detecting elevated levels of NDMA. Millions of blood-pressure pills called angiotensin II receptor blockers were recalled in about 30 countries last year because of concerns about the compound.

FDA Is Testing Diabetes Drug Metformin for NDMA, a Carcinogen

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