In the management of diabetes mellitus, lactic acidosis is caused by which of the following?

Metformin:- S/E: Lactic acidosis Megaloblastic anemia To prevent lactic acidosis, Metformin is to be avoided in high risk patients: Old patients Pt. with renal failure Pt. with liver diseases CHF Tolbutamide (1st gen. Sulfonylureas) - s/e - Hypoglycemia, weight gain. Glipizide (2nd gen. Sulfonylureas) - s/e - Hypoglycemia Pioglitazone - acts by stimulating PPAR-g - reversal of Insulin resistance, s/e - hepatotoxic, edema and Increased risk of urinary bladder cancer