Metronidazole induced liver injury: a rare immune mediated drug reaction.

Drug induced liver injury (DILI) can result either from dose-dependent direct hepatotoxicity or from an unpredictable dose-independent idiosyncratic reaction. Incidence of idiosyncratic DILI is estimated to be approximately 10-15 per 100,000 patient years. Here we report an extremely rare case of metronidazole induced delayed immune-allergic hepatocellular liver injury masquerading as autoimmune hepatitis. A previously healthy 54-year-old Caucasian male, who was treated with metronidazole for Clostridium difficile associated diarrhea, presented 3 months later with right upper quadrant abdominal pain. Laboratory tests revealed total bilirubin level of 12.7 mg/dL, direct bilirubin of 7.2 mg/dL, alanine aminotransferase (ALT) of 973 IU/L, aspartate transaminase (AST) of 867 IU/L, alkaline phosphatase (AP) of 96 IU/L, and an INR of 1.9, suggestive of hepatocellular pattern of injury. A detailed workup for hepatitis revealed no other etiology. A clinical diagnosis of metronidazole induced liver injury was made. With a persistent rise in his bilirubin and transaminase levels, the patient was started on oral prednisone. At the 2-week posthospitalization follow-up visit, the patient reported a significant improvement in his overall sense of being well and liver functions tests trended down substantially (total bilirubin 7.2 mg/dL, ALT 420 IU/L, AST 276 IU/L, AP 183 IU/L, and INR 1.5).