Fidaxomicin is a bactericidal-type antibiotic that inhibits RNA polymerase sigma subunit. RNA polymerase is responsible for transcription in the bacteria therefore fidaxomicin will inhibit protein synthesis. As a result, apoptosis is triggered in susceptible organisms such as C. difficile.
The minimum inhibitory concentration for 90% of organisms for fidaxomicin against C. difficile is 0.9978 to 2 µg/mL.
Fidaxomicin is hydrolyzed by gastric acid or intestinal microsomes into a less active metabolite (OP-1118). The cytochrome enzyme system are not involved in the metabolism of fidaxomicin.