Alteration of FDG uptake associated with metformin: Pitfall and opportunity

Abstract

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Objectives: Metformin, a biguanide molecule with 15 hour half life, is commonly utilized in the treatment of non-insulin-dependent diabetes mellitus. The major effect of metformin is postulated to be enhanced glucose utilization. In vivo and in vitro studies have demonstrated that metformin stimulates the insulin-induced glucose uptake into skeletal muscle and adipocytes in both diabetic individuals and animal models. It has also been shown that insulin-mediated visceral fat glucose uptake (VFGU) is enhanced by metformin monotherapy which is believed to be related to enhanced VF insulin sensitivity. Administration of metformin is routinely discontinued prior to administration of contrast for a CT study. The purpose of the study was to demonstrate and quantify the alteration in FDG uptake in subcutaneous tissue and peripheral striated muscle associated with the use of metformin. Methods: PET images were obtained on fifteen patients who had taken metformin either within four hours prior to an FDG PET examination, between four and twelve hours, or more than twelve hours prior to the study. Subjective and quantitative analysis was made of the distribution and ratio of uptake in the striated muscles and subcutaneous tissue. Results: Patients who received metformin within 12 hours of a PET study were found to have significantly increased uptake in their peripheral musculature and in their subcutaneous fat diffusely as judged subjectively and utilizing ratios of uptake with that in the liver and lungs in comparison to those that did not receive metformin within that time period. Conclusions: Metformin should be discontinued at least 12 hours prior to performing a PET study regardless of whether intravenous CT contrast material is administered. PET may also help quantify the impact of metformin therapy on diabetic patients which could have treatment selection implications.