The hyperlactatemic effect of biguanides: a comparison between phenformin and metformin during a 6-month treatment

To compare the chronic hyperlactatemic effect of phenformin and metformin, we performed a double-blind study in 10 non insulin-dependent diabetics without any other known hyperlactatemic condition. After a pre-study period, each patient was allocated to a 6-month treatment with phenformin (50 mg bid) or metformin (850 mg bid) in random sequence. Body weight values were not significantly different between phenformin and metformin. Diabetic control was significantly (p less than 0.001) improved by both biguanides versus pre-study, but was the same during metformin and phenformin: HbAI = 13.8 +/- 0.3 SEM% during pre-study 9.7 +/- 0.2% during phenformin, 10.2 +/- 0.2% during metformin. Mean values of plasma lactate during metformin were significantly lower versus phenformin (1.30 +/- 0.05 vs 1.64 +/- 0.05 mmol/l, p less than 0.001). Mean values of plasma lactate/pyruvate ratio during metformin were significantly lower versus phenformin (16.92 +/- 0.59 vs 22.65 +/- 0.87, p less than 0.001), but not versus pre-study (16.19 +/- 0.51). These results indicate that: 1) during a 6-month treatment with a diabetic control of similar degree phenformin produces a significantly higher hyperlactatemic effect vs metformin; 2) metformin treatment is associated with less impairment of intracellular redox state versus phenformin, and therefore should be considered advantageous in the long-term treatment of non insulin-dependent diabetics.