Metabolic effects of glucocorticoid and ethanol administration in phenformin- and metformin-treated obese diabetics.

Glucocorticoid administration for 24 hours to phenformin-treated obese diabetics increased blood lactate and lactate/pyruvate (L/P) ratio to higher levels than those found when only one drug was given. In one of 10 subjects, a metabolic acidosis with a blood lactate of 6.2 mmol developed during simultaneous administration of the two drugs. Diabetics treated with phenformin or metformin in equipotent dosages exhibited the highest blood lactate, L/P ratio, andβ-hydroxybutyrate levels during phenformin treatment, both before and during glucocorticoid administration. Ethanol administration to biguanide-treated diabetics resulted in identical increases in blood lactate and L/P ratio during phenformin and metformin treatment. These findings are consistent with the hypothesis that phenformin has a stronger inhibitory effect of gluco-neogenesis than metformin. This may be one reason why lactic acidosis is seen much more often in phenformin-than metformin-treated patients.