Drug-induced liver injury in humans: the case of ximelagatran.

Ximelagatran was the first orally available direct thrombin inhibitor under clinical development that also reached the market. Ximelagatran was tested in an extensive clinical programme. Short-term use (<12 days) in humans including the phase III clinical trials did not indicate any hepatotoxic potential. Increased hepatic enzyme levels were first observed at a higher frequency when evaluating the long-term (>35 days) use of ximelagatran (incidence of >3x upper limit of normal (ULN) plasma ALT was 7.9%). The frequency of elevated total bilirubin levels was similar in the ximelagatran and the comparator groups. However, the combination of ALT > 3x ULN and total bilirubin > 2xULN was 0.5% among patients treated with ximelagatran and 0.1% among patients in the comparator group. Symptoms such as fever and rash potentially indicating hypersensitivity (immunologic type of reaction) were low and did not differ between ximelagatran and the comparators. The withdrawal of ximelagatran from the market and termination of the ximelagatran development program was triggered by safety data from a 35-day study, indicating that severe hepatic injury in a patient could develop after exposure to the drug has been completed and that regular liver function monitoring may not mitigate the possible risk of severe hepatic injury. As for many drugs causing liver injury, the standard preclinical toxicological studies provided no indication that ximelagatran affected hepatic functions. In addition, extensive investigations using human-based in vitro models have not been able to define mechanisms explaining the pattern of hepatic injury observed in long-term clinical trials. A pharmacogenomic study provided evidence that the ALT increases were associated with major histocompatibility complex (MHC) alleles DRB1'07 and DQA1*02 suggesting a possible immunogenic pathogenesis. This example provides important clues to the mechanism of idiosyncratic drug-induced liver toxicity.