Serum bicarbonate: can it be a marker of metformin induced acidosis in geriatrics?

Metformin is an oral antidiabetic agent, widely used in the treatment of type 2 diabetes mellitus. The serious side effect of metformin therapy is lactic acidosis. Contraindications for metformin therapy include renal insufficiency. A cut off value of 60 ml/min in creatinine clearance is suggested. Hundred type 2 diabetics receiving metformin as monotherapy or in combination with insulin/other oral antidiabetic agents, were enrolled in the study. Patients were on metformin for atleast one month prior to being enrolled. Patients' demographic data were taken. Baseline serum creatinine and bicarbonate were estimated. Creatinine clearance (Clcr ml/ min) was calculated. Patients were grouped into group 1-4 depending upon the doses of metformin they received. Patients were again grouped based on their Clcr as groupA (Clcr < 60 ml/min), group B (Clcr > 60.01 ml/min). Data was analysed using student's t test. Out of 100 patients 52 were males, 48 females. Mean age and SD of males and females were 69.92 +/- 6.95 and 66.85 +/- 5.72 respectively. Comparison of mean bicarbonate level in different doses of metformin did not show any statistical significance. But comparison of bicarbonate levels based on Clcr were highly statistically significant (p = 0.0084). In three patients whose bicarbonate level was very low (15, 16.4 and 19.2 mmol/L), doses of metformin was reduced and after one month their bicarbonate levels returned to normal (27.4, 25.6 and 26.2 mmol/L). Hence serum bicarbonate can be a marker to assess metformin induced acidosis in geriatrics patients with low creatinine clearance.