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Low levels of contamination with N-nitrosodimethylamine (NDMA)

18 November 2020

The TGA began investigating the potential contamination of Australian metformin medicines with N-nitrosodimethylamine (NDMA) in late 2019.

Recently, TGA's laboratories completed testing a selection of immediate- and extended-release metformin medicines for the presence of NDMA. This 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, and it has now been recalled from wholesalers.

Metformin is an important treatment for diabetes. The risks from not treating diabetes are far greater than the risks posed by the levels of NDMA seen to date.

The TGA has carefully considered the risk for patients from batches that modestly exceed the limit. This included an analysis of the commonly prescribed doses of metformin using data from the general practice program MedicineInsight. Overall, the risk is considered to be very low for patients on both immediate- and extended-release products. 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. 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 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. The TGA is also working with medicine manufacturers to oversee the implementation of improved manufacturing and testing processes that will ensure that metformin medicines supplied in Australia meet our high standards for quality.

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