Effect of metformin on ¹⁸F-fluorodeoxyglucose uptake and positron emission tomographic imaging

Metformin is widely used to treat diabetes, but induces changes in glucose uptake in both normal organs and tumors. Here, we review the effects of metformin on the uptake of ⁸F-fludeoxyglucose (¹⁸F-FDG) in tissues and tumors, and its influence on ¹⁸F-FDG positron emission tomographic imaging (¹⁸F-FDG PET), as well as the mechanisms involved. This is an important issue, because metformin has diverse effects on tissue uptake of ¹⁸F-FDG, and this can affect the quality and interpretation of PET images. Metformin increases glucose uptake in the gastrointestinal tract, cerebral white matter, and the kidney, while regions of the cerebrum associated with memory show decreased glucose uptake, and the myocardium shows no change. Hepatocellular carcinoma and breast cancer show increased glucose uptake after metformin administration, while thyroid cancer shows decreased uptake, and colon and pancreatic cancers show no change. A high-energy diet increases ¹⁸F-FDG uptake, but this effect is blocked by metformin. Withdrawal of metformin 48 h before PET image acquisition is widely recommended. However, based on our review of the literature, we propose that the differentiation of metformin discontinuation could be reasonable. But future clinical trials are still needed to support our viewpoint.