Faldaprevir (FDV), a substrate of CYP3A/P-glycoprotein (P-gp), is a selective inhibitor of the hepatitis C virus (HCV) NS3/4 protease. FDV is currently under clinical development for application in interferon-free treatment regimens for patients with chronic HCV infection. Understanding the drug-drug interaction potential of FDV is critical, as certain drug combinations may facilitate the more rapid achievement of steady-state-that is, the ideal drug concentration and balanced metabolic cycle of absorption and elimination that optimize drug efficacy. We thus conducted this study to investigate the effect of itraconazole (ICZ), a strong inhibitor of CYP3A and a moderate inhibitor of P-gp, on the pharmacokinetics (PK) of FDV. Eighteen healthy male and female volunteers participated in this open-label, fixed-sequence study. FDV 120 mg twice daily (BID) was administered on Day 1, followed by 120 mg once daily (QD) from Day 2 until the end of the 10-day study; after 6 days of FDV alone, ICZ 200 mg was added to FDV for an additional 4 days (BID on Day 7 and QD from Day 8 to Day 10). Intensive PK sampling was performed after 6 days of FDV treatment and again after 4 days of combined FDV/ICZ treatment. The adjusted geometric mean (gMean) ratios (%) of area under the concentration curve over dosing interval at steady-state (AUCτ, ss) and maximal concentration at steady-state (Cmax, ss) for combined FDV/ICZ treatment vs. FDV treatment alone were 198.6% and 180.6%, respectively, with 90% confidence intervals (CIs) of 182.4-216.1 and 165.7-196.9. Administration of FDV alone or in combination with ICZ was observed to be safe and well-tolerated. Co-administration with ICZ, however, resulted in an approximately two-fold increase in FDV steady-state exposure. Furthermore, FDV required no dosage adjustment when co-administered with ICZ.