Drug Interactions between fidaxomicin and Omeclamox-Pak

Although some in vitro data indicate synergism between macrolide antibiotics and penicillins, other in vitro data indicate antagonism. When these drugs are given together, neither has predictable therapeutic efficacy. Data are available for erythromycin, although theoretically this interaction could occur with any macrolide. Except for monitoring of the effectiveness of antibiotic therapy, no special precautions appear to be necessary.

Clarithromycin may increase and prolong the omeprazole plasma concentration. The mechanism may be related to clarithromycin inhibition of hepatic cytochrome P450 enzymes responsible for omeprazole metabolism. Coadministration of omeprazole may result in an increase in clarithromycin and 14-(R)-hydroxyclarithromycin plasma concentrations. These increases may be due to the effect of omeprazole on gastric pH.

Coadministration with inhibitors of P-glycoprotein (P-gp) may increase the plasma concentrations of fidaxomicin and its main metabolite, OP-1118, both of which are substrates of the intestinal efflux transporter. When fidaxomicin 200 mg was administered in combination with cyclosporine 200 mg in 14 study subjects, fidaxomicin peak plasma concentration (Cmax) and systemic exposure (AUC) increased by an average of 4.2- and 1.9-fold, respectively, compared to when administered alone. The Cmax and AUC of OP-1118 was increased by 9.5- and 4.1-fold, respectively, with cyclosporine. Theoretically, concentrations of fidaxomicin and OP-1118 may also be decreased at the site of action (i.e., gastrointestinal tract) due to P-gp inhibition. However, concomitant use of a P-gp inhibitor had no attributable effect on safety or efficacy of fidaxomicin in controlled clinical trials. No dosage adjustment is recommended when fidaxomicin is coadministered with P-gp inhibitors.