Studies on the Site and Mechanism of Action of Phenformin: I. Evidence for Significant “Nonperipheral” Effects of Phenformin on Glucose Metabolism in Normal Subjects

Oral and intravenous glucose tolerance tests were performed in ten normal subjects. Phenformin pretreatment flattened the glucose and insulin response to oral glucose loading but did not significantly alter the response to intravenous glucose. It is suggested that these results can best be explained by an inhibitory effect of the drug on the rate of intestinal glucose absorption.