A 54- year old obese patient with type 2 diabetes mellitus and a history of alcoholism probably should not receive metformin because it can increase the risk of:

(Ref: KDT 6/e p269) Biguanides like metformin and phenfOrmin increase the risk of lactic acidosis paicularly in the patients with hepatic or renal disease. Both these drugs can cause lactic acid05is although phenformin has more potential to cause this adverse effect than metformin. Metforrnin is more likely to cause megaloblastic anemia than phenformin.