Avoiding N-nitrosodimethylamine formation in metformin pharmaceuticals by limiting dimethylamine and nitrite.

Since late 2019, concerns regarding trace levels of the probable human carcinogen N-dimethylnitrosamine (NDMA) in Metformin-containing pharmaceuticals have been an issue if they exceeded the maximum allowable intake of 96 ng/day for a medicine with long-term intake. Here, we report results from an extensive analysis of NDMA content along the active pharmaceutical ingredient (API) manufacturing process as well as two different drug product manufacturing processes. Our findings confirm that Metformin API is not a significant source of NDMA found in Metformin pharmaceuticals and that NDMA is created at those steps of the drug product manufacturing that introduce heat and nitrite. We demonstrate that reduction of nitrite from excipients is an effective means to reduce NDMA in the drug product. Limiting residual dimethylamine in the API has proven to be another important factor for NDMA control as dimethylamine leads to formation of NDMA in the drug products. Furthermore, analysis of historical batches of drug products has shown that NDMA may increase during storage, but the levels reached were not shelf-life limiting for the products under study.

NDMA analytics in metformin products: Comparison of methods and pitfalls.

BACKGROUND: For nearly three years, the concerns regarding trace levels of N-nitrosamines in pharmaceuticals and the associated cancer risk have significantly expanded and are a major issue facing the global pharmaceutical industry. N-nitrosodimethylamine (NDMA) found in formulations of the popular anti-diabetic drug metformin is a prominent example. This has resulted in product recalls raising the profile within the media. Issues of method robustness, sample preparation and several unexpected sources of nitrosamine contamination have been highlighted as false positive risks. It has become apparent that the identification of the root causes of artefactual formation of nitrosamines must be identified to mitigate risk associated with the analysis. METHODS: A comparison study between four laboratories, across three companies was designed, employing orthogonal mass spectrometric methods for the quantification of NDMA in two metformin immediate release (IR) formulations and one extended release (XR) formulation. These were 2x LC-MS/MS, GC-MS/MS and GC-HRMS. RESULTS: Good agreement of results was obtained for the IR formulations. However, we measured higher concentrations of NDMA in the XR formulation using GC-MS/MS compared to LC-MS/MS. We could show that this was due to artefactual (in situ) formation of NDMA when samples were extracted with dichloromethane. Removal of dimethylamine (DMA) and nitrite from the extracted sample or the addition of a nitrosation scavenger are shown to be effective remedies. NDMA in situ formation was not observed in 10% MeOH or acetonitrile. CONCLUSION: Metformin pharmaceuticals contain traces of the API impurity DMA as well as inorganic nitrite from excipients. This can lead to artefactual formation of NDMA and hence false positive results if DCM is used for sample extraction. Similar artefacts are likely also in other pharmaceuticals if these contain the secondary amine precursor of the respective nitrosamine analyte.