A 44-year-old man hospitalized for septic arthritis in the background of polyarticular gout developed worsening anion gap metabolic acidosis (AGMA) over the course of 10 days. Acetaminophen was dosed as needed on hospital days 0-10 (mean 1,530mg/day), then scheduled at 1,000mg every 6 hours (4,000mg/day) starting on hospital day 11. The anion gap developed on hospital day 8 and then continued (Fig 1). Daily monitoring revealed decreased oral intake during the hospital stay. Beta-hydroxybutyrate (BHB) level was normal until it became elevated to 2.2mmol/L on hospital day 16; glucose and lactic acid levels were normal throughout the stay.