The effect of oral and intravenous administration of butylbiguanide on the oral glucose tolerance test was investigated in 12 normal human volunteers. Orally administered butylbiguanide lowered the oral glucose tolerance curve and the corresponding serum insulin values, whereas intravenously injected butylbiguanide had no effect. 2. The lactate/pyruvate ratio determined 180 min. after glucose ingestion increased after oral butylbiguanide administration. No effect was observed after intravenous administration. 3. The decrease in serum phosphate levels observed after oral glucose loading was not influenced by butylbiguanide administered by either route. In addition, no effect of this drug was observed on fasting levels of glucose, insulin, phosphate, bicarbonate, lactate and pyruvate. 4. These results are compatible with recent observations that biguanides inhibit active transport mechanisms in the intestine. In addition, the effect of biguanides on blood levels of glucose metabolites is discussed with respect to their known action on oxidative phosphorylation.
