Hypersensitivity. Lactic acidosis, diabetic ketoacidosis; diabetic pre-coma; severe renal failure (GFR <30 mL/min); acute conditions eg, dehydration, severe infection, shock, intravascular administration of iodinated contrast agents, acute or chronic disease which may cause tissue hypoxia eg, cardiac or resp failure, recent MI, shock, hepatic impairment, acute alcohol intoxication, alcoholism. Breastfeeding.