Mere months after reassuring the public that metformin was safe, the U.S. Food & Drug Administration (FDA) has acknowledged that a new round of tests detected excessive levels of a potentially cancer-causing chemical in some extended release versions of the popular diabetes drugs.
According to sources who spoke with Bloomberg News earlier this week, the FDA could order metformin recalls in a matter of days.
Metformin is the most widely used oral treatment for Type 2 diabetes. Last year, doctors in the United States wrote about 21 million prescriptions for extended-release versions, accounting for roughly a quarter of all metformin prescriptions.
Regulators in Singapore first discovered high levels of N-Nitrosodimethylamine (NDMA) – a probable human carcinogen — in some metformin tablets late last year, resulting in a recall for six lots in that country. Similar metformin recalls have since been announced in Canada. However, the FDA declined to order any metformin recalls in the United States after reassuring the public that its own tests hadn’t detected NDMA above acceptable limits.
But in March, the online pharmacy Valisure disclosed that its testing program had detected excessive levels of NDMA in 16 of 38 metformin samples tested, including some tablets that contained more than 10-times the FDA’s recommended daily limit of 96 nanograms. The company petitioned the agency for a recall of the affected lots, as well an investigation to determine how the contamination had occurred.
According to a report posted by Valisure on Tuesday, a new round of tests on 128 metformin samples detected excessive levels of NDMA in 36%. Valisure apparently obtained those samples from consumers across the United States.
“The presence of this carcinogen in metformin where multiple tablets can be taken daily and often for a lifetime diabetic condition, makes this finding particularly concerning,” Deanna Akinbajo, chief pharmacist at Valisure, said in a statement.
The FDA confirmed finding high levels of NDMA in extended release versions of metformin on Wednesday, but would not disclose which companies’ products were affected. According to Bloomberg News, the agency is in the process of contacting those drug makers.
“We cannot confirm or deny a recall action before it has taken place,” Sarah Peddicord, an agency spokesperson, said in a statement. The FDA “will continue to take quick and appropriate action when needed to protect American consumers.”
The agency hasn’t found elevated NDMA levels in immediate-release metformin, Peddicord said. She also warned that patients shouldn’t stop taking their metformin without first consulting their doctor.
This incident marks the second time Valisure has warned the FDA about the presence of NDMA in a popular medication. Last September, testing conducted by the company found high levels of the carcinogen in Zantac and other ranitidine-containing heartburn drugs. In April, the agency ordered all versions of Zantac removed from the market after confirming that levels of NDMA can increase in ranitidine over time.