1. Circulating concentrations of intermediary metabolites have been measured after administration of 50 mg of phenformin to normal subjects.
2. Phenformin caused a significant increase in blood lactate, alanine and the lactate/pyruvate ratio but did not affect blood glucose or serum insulin concentrations.
3. There was a significant correlation between the increase in blood lactate concentration after phenformin and the plasma concentration of the drug.