NEW YORK • High levels of the probable carcinogen NDMA have been found in the US supply of the widely used diabetes drug metformin, according to testing done by online pharmacy Valisure, which is pressing regulators for recalls.
Valisure's testing found NDMA in 16 different batches of metformin made by 11 drug companies, including Amneal Pharmaceuticals, Ascend Laboratories and Actavis Pharma.
A type of nitrosamine, NDMA - or N-nitrosodimethylamine - is classified as potential carcinogens for humans.
The highest levels detected were in a batch made by Amneal, which had as much as 16 times the acceptable daily limit of NDMA, according to Valisure's findings.
Metformin, often used as an initial treatment for individuals with type 2 diabetes to control high blood sugar levels, is the fourth most commonly prescribed drug in the United States.
In a citizen's petition submitted to the Food and Drug Administration (FDA) on Monday, Valisure asked the regulator to request a recall and investigate what happened with the contaminated products.
Mr Peter Cassell, a spokesman for the FDA, said that the regulator will respond directly to Valisure.
In December, the FDA said it was testing samples of metformin sold in the country for NDMA, and that it would recommend recalls of the medication as appropriate.
European drug regulators have told companies to test for high levels of the carcinogen in metformin.
Recent testing by the FDA has found low levels of NDMA in some metformin, but in none of those tests were levels found to be higher than the acceptable intake limit of 96 nanograms a day, according to a statement last month.
There were metformin recalls in Singapore late last year and in Canada last month, but so far the US has not followed suit.
Singapore's Health Sciences Authority said in December that three metformin drugs were found to contain NDMA, in trace amounts that are above the internationally acceptable level. The recalled drugs were: one batch of the Glucient XR 500mg tablet, supplied by Glorious Dexa Singapore; and all batches of Meijumet prolonged-release tablet in 750mg and 1,000mg versions, supplied by Pharmazen Medicals.
Singapore's Health Sciences Authority said in December that three metformin drugs were found to contain NDMA, in trace amounts that are above the internationally acceptable level.
The recalled drugs were: one batch of the Glucient XR 500mg tablet, supplied by Glorious Dexa Singapore; and all batches of Meijumet prolonged-release tablet in 750mg and 1,000mg versions, supplied by Pharmazen Medicals.
The FDA has said it will continue to monitor NDMA in metformin and other drug products and provide updates on recalls.
NDMA has also been found in other drugs, including the blood-pressure medication valsartan and heartburn drug ranitidine, prompting recalls. NDMA can also be found in lower levels in cured and grilled meats, dairy products and vegetables, the FDA has said.
"Everyone is exposed to some level of NDMA. The FDA and the international scientific community do not expect it to cause harm when ingested at low levels," Dr Janet Woodcock, a physician and director of the FDA's Centre for Drug Evaluation and Research, said in December.
It is unclear why Valisure's results differ from the FDA findings. Valisure said it largely followed the FDA's protocol for testing for NDMA in metformin, except for changes that it said were made to make the method more precise.
Valisure's founder and chief executive officer David Light said it was also possible the FDA got samples that were not representative of the general drug supply.
Depending on the product, NDMA contamination could have occurred during the manufacturing process. It could also be due to how a drug is stored, or even aspects of the drug itself.
In metformin, Valisure believes the contamination may have originated in manufacturing, but it was possible aspects of the drug itself may have contributed, said Mr Light.