To evaluate the effect on the nonsteroidal anti-inflammatory drug indomethacin on Clostridium difficile infection (CDI) severity. Materials & methods: Indomethacin was administered in two different mouse models of antibiotic-associated CDI in two different facilities, using a low and high dose of indomethacin. Results: Indomethacin administration caused weight loss, increased the signs of severe infection and worsened histopathological damage, leading to 100% mortality during CDI. Indomethacin-treated, antibioticexposed mice infected with C. difficile had enhanced intestinal inflammation with increased expression of KC, IL-1β and IL-22 compared with infected mice unexposed to indomethacin. Conclusion: These results demonstrate a negative impact of nonsteroidal anti-inflammatory drugs on antibiotic-associated CDI in mice and suggest that targeting the synthesis or signaling of prostaglandins might be an approach to ameliorating the severity of CDI.