The recognition of the rarity of lactic acidosis among users of metformin with renal insufficiency has changed recommendations to allow for its use in patients with mild to moderate renal insufficiency. Current guidelines use an estimated GFR (eGFR) which is a more accurate approximation of renal function than serum creatinine. The current recommendation of the American Diabetes Association states that metformin can be used at full doses (2000 mg/day) as long as eGFR > 45 ml/min and serum creatinine is monitored. If the eGFR is < 45ml/min, then a maximal dose of 1000 mg/day is advised, with serum creatinine monitoring. Metformin should not be used if the eGFR is < 30 ml/min (10).