Fasting plasma lactate concentrations in ambulatory elderly patients with type 2 diabetes receiving metformin therapy: a retrospective cross-sectional study.

BACKGROUND Metformin is a worldwide accepted biguanide antidiabetic agent, and its effectiveness and benefit have already been well established. Among the side effects of metformin, lactate acidosis is the most problematic because of a high mortality rate, which impedes its use in clinical practice, especially in elderly patients with type 2 diabetes. Aging is associated with a decreased renal function and increasing comorbidities, but few data are available regarding plasma lactate levels in this unique population. In this study, we assessed fasting plasma lactate levels in ambulatory, elderly Taiwanese patients with type 2 diabetes, who were taking the drug, metformin, to identify independent risk factors for hyperlactemia in this group. METHODS Sixty-six ambulatory type 2 diabetic patients, > 80 years of age (mean, 83.6 years; range, 80-90 years), receiving metformin therapy, were enrolled, from January 2005 to September 2009, in the Diabetes Case Management Program. A further 79 younger patients (also type 2 diabetics on metformin) served as controls (mean age, 59.9 years; range, 37-79 years). Fasting serum electrolytes, creatinine, bicarbonate, glycated hemoglobin, plasma glucose and lactate levels were determined. RESULTS Lactate levels did not differ between the elderly and control groups (13.2 +/- 5.2 mg/dL and 13.5 +/- 4.8 mg/dL, respectively). None of the patients fulfilled the lactic acidosis criteria. Patients in the elderly group had a significantly lower daily metformin dose, higher creatinine levels, and lower estimated creatinine clearance, compared with the control group (all p < 0.05). Estimated creatinine clearance was negatively associated with lactate levels in the elderly group (p < 0.05, r = -0.27), but not in the control group. Patients with fasting plasma glucose levels > 130 mg/dL had a 2.8-fold increased risk of developing hyperlactemia. CONCLUSION Plasma lactate levels in ambulatory elderly patients with type 2 diabetes receiving metformin therapy did not differ from those in a younger age group. Patients with fasting plasma glucose levels > 130 mg/dL had a 2.8-fold risk of developing hyperlactemia, but none of them developed lactate acidosis.