Mixed findings on Metformin contamination


27699468 - tablet with the chemical formula of metformin

Reassuring messages from TGA after investigation reveals some contaminated Metformin batches 

The risk to patients who have taken metformin that is potentially lightly contaminated with a potentially carcinogenic nitrosamine has been ruled to be “very low” by the Therapeutic Goods Administration.

However, it did find that almost a third of tested metformin batches did contain N-nitrosodimethylamine (NDMA), a type of N-nitroso compound that may be carcinogenic with long-term exposure.

The TGA launched an investigation into metformin in late 2019 after it became “aware that some overseas regulators have detected low levels of NDMA in a small number of metformin products”.

“Recently, the TGA’s laboratories completed testing a selection of immediate- and extended-release metformin medicines for the presence of NDMA,” it said in a release issued today (18 November).

“This research found that approximately 30% of batches contained levels of NDMA that modestly exceed the acceptable limit (less than twice the limit)”.

One batch was found to have higher levels (4.4‑times the limit). Only limited stock of this batch has been supplied, the TGA said, and it has now been recalled from wholesalers.

The TGA says it has “carefully considered the risk for patients from batches that modestly exceed the limit”.

“Overall, the risk is considered to be very low for patients on both immediate- and extended-release products,” it concluded. “The TGA investigation indicates that the majority of patients would not be exposed to levels of NDMA that exceed the acceptable intake limit”.

The limits set by the TGA for NDMA are “very conservative”, it said.

They are calculated to ensure that an individuals’ excess cancer risk would not exceed 1:100,000 if that individual was on the maximum daily dose of the medicine for 70 years.

As most individuals do not take the maximum daily dose, and are not using metformin for this long, the risks are “very low”.

The TGA says it is continuing to work with the sponsors of metformin medicines to ensure that this critical medicine remains available, and that consumers are not exposed to unacceptable levels of NDMA.

Consumers are strongly advised to continue to take their metformin medicines as prescribed, it urges.

N-nitroso compounds are commonly found in low levels in a variety of foods, particularly smoked and cured meats, as well as in some drinking water and in air pollution. Long-term exposure, over many years, can increase an individual’s risk of developing cancer.

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