Metformin is a first line oral medication for diabetes mellitus shown to decrease cardiovascular morbidity and mortality. Though the prevalence of metformin-associated lactic acidosis (MALA) is low, mortality is high, ranging from 25-50%. Therefore, it presents a diagnostic challenge that is critical to identify, particularly in patients with renal impairment at baseline. Traditionally patients with creatinine greater than 1.5 mg/dL have been excluded from using metformin; however, metformin might be acceptable in some patients with chronic kidney disease (CKD).

Case Presentation:

A 69 year old female with a past medical history of diabetes mellitus, hypertension, breast cancer, and no chronic kidney disease was sent to the hospital by her rehabilitation facility secondary to her being found unresponsive. This was in the presence of decreased appetite and impaired mobility limiting her ability to feed herself in the 2 weeks prior to hospital admission. Her medications included metformin, insulin glargine, anastrazole, and hydrochlorothiazide. She had nausea and vomiting the night prior to admission. Despite her decreased oral intake, she continued taking her full dose of metformin and insulin throughout that two week period. On arrival to the emergency room, her vitals were rectal temperature 90.6° F, heart rate 66 beats per minute, blood pressure 60/40 mmHg, respiratory rate 25 breaths per minute, and oxygen saturation 88% on room air. Her Glasgow Coma Scale was 2 with physical exam findings significant for limited withdrawal to noxious stimuli. Her initial labs were significant for bicarbonate of 2 mEq/L (normal range 24-32 mEq/L), potassium of 6.7 mEq/L (normal range 3.5-5.0 mEq/L), blood urea nitrogen of 110 mg/dL (normal range 7-26 mg/dL), creatinine of 9.7 mg/ dL (normal range 0.7-1.4mg/dL) with a baseline of 0.7 mg/ dL 2 months ago, and lactate of 26 mmol/L (normal range 0.5-2.2 mmol/L). A venous blood gas was significant for a pH of 6.65. Plasma metformin level was not available.