Recent studies have demonstrated that phenformin inhibits intestinal glucose absorption in man. In order to determine if carbohydrate malabsorption occurs during phenformin administration we used a breath hydrogen (H2) test. This test depends upon fermentation of unabsorbed carbohydrate to hydrogen by colonic bacteria with subsequent absorption of H2 and pulmonary excretion. H2 excretion rates were measured in five normal subjects while fasting and two hours after the administration of 75 gm. of glucose. The study was repeated on the following day after the administration of 100 mg. of phenformin. There was no significant change in H2 excretion. One subject was then studied several times a day while eating a normal diet; phenformin administration did not increase H2 excretion. We conclude that the drug does not induce carbohydrate malabsorption.

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