Common adverse reactions of fidaxomicin are vomiting, nausea and constipation. These side effects may potentially be porphyrinogenic if leading to a decrease in carbohydrate intake.

Fidaxomicin has a very low systemic absorption following oral administration. It is a weak and clinically insignificant inhibitor of CYP 3A4, 2C9 and 2C19, and porphyrinogenic effects are not suspected.

Macrocyclic antibiotic.

Fidaxomicin is used in the treatment of Clostridium difficile infections. It is administered orally.

Fidaxomicin is largely confined in the gastrointestinal tract and has a very low systemic distribution. It is hydrolyzed by gastric acid or intestinal microsomes into a less active metabolite (OP-1118). Fidaxomicin is not metabolized by CYP (Drugbank, SPC). Fidaxomicin is a substrate of P-gp, and co-administration of P-gp inhibitors may increase the Cmax and AUC of fidaxomicin (SPC). In vitro studies have suggested that systemic interactions caused by CYP inhibition or induction are unlikely (EMA, scientific discussion). An in vivo study with CYP 3A4, 2C9 and 2C19 substrates indicates that that fidaxomicin has weak, but not clinically relevant inhibitory effects on these enzymes (EMA, Vaishnavi 2015, FDA label). The half-life of fidaxomicin is approximately 8-10 h.