Correlation of plasma phenformin concentration with metabolic effects in normal subjects.

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.