Metformin is the first choice oral antidiabetic drug for type 2 diabetes and currently the most consumed. Although gastrointestinal intolerance is frequent, metformin-induced hepatotoxicity is rare. Fewer than 10 cases have been reported (1). In all of those cases, metformin was associated with concomitant intake of other potentially hepatotoxic drugs. We present what we feel may be the first documented case of hepatotoxicity due to metformin with no other drug interference. A 61-year-old man was admitted to the hospital with a 3-day history of painless jaundice. He had no history of liver disease or toxic habits and denied previous consumption of drugs or herbal products, but had been taking metformin (1,700 mg/day for 6 weeks) after being diagnosed with type 2 diabetes.

Laboratory tests showed a mixed pattern of liver damage (total bilirubin 2.9 mg/dL, direct bilirubin 2.4 mg/dL, aspartate aminotransferase [AST] 290 units/L [# 40], alanine aminotransferase [ALT] 861 units/L [# 35], γ-glutamyltransferase [GGT] 861 units/L [# 35], and alkaline phosphatase [ALP] 622 units/L [# 120]). International normalized ratio and eosinophil counts were normal. Diagnostic work-up ruled out viral hepatitis A, B, and C, as well as autoimmune and metabolic liver disease (negative antinuclear antibodies, anti-mitochondrial antibodies, smooth muscle antibodies, anti-liver/kidney microsomal antibodies; normal ceruloplasmin, α-1 antitrypsin, copper). Abdominal ultrasound and cholangio-MRI showed no pathological findings. The patient refused a liver biopsy. After stopping metformin, the patient’s clinical condition progressively improved and liver enzymes normalized in 30 days. He was discharged with only recommendations to modify his lifestyle. Six weeks after discharge, the patient again developed malaise, nausea, and