Finding the sweet spot for metformin in 18F-FDG-PET

The effect of oral hypoglycemic agents on fluorine-18-flurodeoxyglucose (F-FDG) uptake is less understood than the effect of exogenous insulin. In this study, the effect of withholding metformin on F-FDG distribution in subsequent PET imaging was evaluated.

A retrospective observational study was carried out. A total of 15 patients taking metformin were grouped according to the time interval from the last dose of metformin to F-FDG-PET. Those who received PET after stopping metformin for less than 24 h were compared with those stopping metformin 24-48 h before PET. The F-FDG uptake and PET image fidelity for these groups were compared qualitatively and the associated blood glucose was recorded. The average standardized uptake value of the liver, tongue, and subcutaneous tissues among the groups were also compared.

The F-FDG-PET distribution and image quality were found to be the best at time points greater than 24 h following metformin dose. There was significantly increased F-FDG uptake in the liver and tongue and tongue-to-liver ratio in patients who had metformin within 24 h of F-FDG-PET compared with those who last had metformin greater than 24 h before F-FDG-PET; however, the F-FDG uptake in the subcutaneous tissues was unchanged.

Less than 24 h between metformin dose and F-FDG-PET resulted in increased muscle and fat uptake in addition to increased bowel uptake. Abnormal F-FDG uptake can limit the diagnostic quality of an exam and affect F-FDG uptake in cancer. The emerging role of biguanides in the treatment of cancer calls for more personalized standardization for F-FDG-PET in the presence of oral hypoglycemic agents.