Increased risk for lactic acidosis w/ topiramate or other carbonic anhydrase inhibitors (eg, zonisamide, acetazolamide or dichlorphenamide). Increased risk of hypoglycemia w/ insulin or insulin secretagogues (eg, sulfonylurea). May tend to produce hyperglycemia & may lead to loss of glycemic control w/ certain drugs eg, thiazides, other diuretics, corticosteroids, phenothiazines, thyroid products, estrogens, OCs, phenytoin, nicotinic acid, sympathomimetics, Ca channel blocking drugs & INH. Decreased serum lithium conc. Metformin: May increase systemic exposure & risk for lactic acidosis in concomitant use w/ drugs that interfere w/ common renal tubular transport systems involved in the renal elimination of metformin (eg, organic cationic transporter-2 [OCT2]/multidrug & toxin extrusion [MATE] inhibitors eg, ranolazine, vandetanib, dolutegravir & cimetidine). Potentiated effect on lactate metabolism w/ alcohol.