OBJECTIVES: Fidaxomicin is the first in a new class of macrocylic antibiotics, indicated in adults for the treatment of Clostridium difficile infections (CDI). The objective was to analyse the cost-utility of fidaxomicin compared to oral vancomycin in the treatment of adult CDI patients. The analysis focused on three CDI patient subgroups : cancer, concomitant antimicrobials, and renal impaired patients. METHODS: A Markov model was developed with a cycle length of 10 days and a one year time horizon. The patient enters the model in the CDI health state and is treated with fidaxomicin, or vancomycin for 10 days. Health state utilities were derived from the literature. The model perspective was the Spanish healthcare provider. Deterministic and probabilistic sensitivity analyses were performed. RESULTS: In all three CDI patient subgroups, fidaxomicin was dominant compared to vancomycin. For cancer fidaxomicin resulted in cost savings of €2,397 with an incremental QALY gain of 0.016. For concomitant antibiotics fidaxomicin resulted in cost savings of €1,452 with an incremental QALY gain of 0.014. For renally impaired, fidaxomicin resulted in cost savings of €1,432 and an incremental QALY gain of 0.013. The main cost-effectiveness drivers were the recurrence rate and length of hospital stay. The probability of fidaxomicin being cost effective at the €30,000 threshold was 96%, 94% and 96% respectively for cancer, concomitant antimicrobials and renal impairment, respectively. CONCLUSIONS: Fidaxomicin was dominant compared to vancomycin for these adult CDI patient subgroups.