OBJECTIVES: Fidaxomicin is the first in a new class of macrocylic antibiotics, indicated in adults for the treatment of Clostridium difficile infections (CDI) also known as C. difficile-associated diarrhoea (CDAD). The study objective was to perform a cost-utility analysis of fidaxomicin for the treatment of CDI compared to oral metronidazole (used to treat initial non-severe CDI and first non-severe recurrence) and oral vancomycin (used to treat severe CDI and any non-severe recurrence beyond the first one). METHODS: A Markov model was used to determine the cost-utility of fidaxomicin in the treatment of all adult CDI patients (base case), patients with severe CDI, and patients with initial CDI recurrences, respectively. The cycle length was 10 days. The patient enters the model in the CDI health state and is treated either with fidaxomicin, oral metronidazole or vancomycin for 10 days. The time horizon was one-year. Deterministic and probabilistic sensitivity analyses were performed.  Health state utilities were derived from the literature. The perspective was that of the Irish Health Service Executive (HSE).  RESULTS: In the base case, fidaxomicin was dominant compared to current standard of care, resulting in cost savings of €2,904 and an incremental QALY gain of 0.031. The main drivers of cost-effectiveness were the reduction in rate of recurrence in patients treated with fidaxomicin and the cost of hospitalisation. Fidaxomicin was also found to be dominant for all patient subgroups. The ICERs were highly sensitive to recurrence rates. The probability of the cost-effectiveness of fidaxomicin in all CDI patients at a willingness to pay threshold of €45,000 per QALY gained was estimated to be approx. 82% CONCLUSIONS: Fidaxomicin was dominant compared to current standard of care with an approx. 82% probability of being cost-effective in all CDI patients at a willingness to pay threshold of €45,000 per QALY gained.