The US Food and Drug Administration has asked five pharmaceutical firms to voluntarily recall their formulations of the diabetes drug metformin after the agency found high levels of a possible cancer-causing impurity.
The FDA said the companies' extended-release versions of the drugs contained the probable carcinogen N-nitrosodimethylamine (NDMA) beyond acceptable limits.
NDMA contamination was responsible for the FDA's recall in April of the heartburn drug Zantac sold by Sanofi, as well as some other, generic versions of the treatment containing the ingredient ranitidine.
An FDA sokeswoman said it had not found elevated NDMA levels in immediate-release metformin.
The FDA, which said it would post the company recall notices on its website, named Canadian company Apotex Corp as one of the firms whose metformin tablets had high levels of NDMA. It has not yet revealed the names of the four other firms.
However, patients should continue taking metformin tablets until their doctors can prescribe a replacement, the agency said.
The FDA started an investigation into metformin, which is used as an initial treatment for patients with type 2 diabetes, in December.
Concerns over NDMA contamination of ranitidine and metformin formulations were raised by the online pharmacy Valisure.
Valisure said in March that its independent tests showed high levels of NDMA in metformin made by 11 companies, including Amneal Pharmaceuticals and Aurobindo Pharma.
Tests on 38 batches of metformin from 22 companies found that 16 batches from 11 companies had NDMA exceeding the FDA’s acceptable daily level of 96 nanograms, Valisure said. Several batches contained levels 10 times the daily acceptable intake limit.
A nanogram is one-billionth of gram.
NDMA is believed to be toxic to the liver and a possible factor in cancers of the stomach and bladder. It is found at low levels in processed foods such as cold meats and cheese and in alcoholic drinks and tobacco smoke.
Several brands of the blood pressure medication valsartan were recalled in 2018 and 2019 because of NDMA contamination.
