The Pharmacokinetics of the CYP3A Substrate Midazolam After Steady-state Dosing of Delafloxacin.

Purpose: Delafloxacin is a novel anionic fluoroquinolone in Phase III development for the treatment of serious skin infections. The objective of this study was to evaluate the effects of delafloxacin on the pharmacokinetics of midazolam, a cytochrome P450 (CYP) 3A substrate.

Methods: CYP3A activity using midazolam as a probe was assessed before and after multiple doses of delafloxacin to reach steady state. In this nonrandomized, open-label, single-sequence, Phase I study, 22 healthy male and female subjects were administered a single 5-mg oral dose of midazolam on days 1 and 8, with oral delafloxacin 450 mg every 12 hours administered from days 3 to 8. Full pharmacokinetic profiles were obtained on days 1 and 8 (midazolam and 1-hydroxymidazolam) and days 3 and 7 (delafloxacin).

Findings: The geometric mean ratios (90% CIs) for AUC and C of midazolam coadministered with delafloxacin versus midazolam alone were 89.4 (83.2-96.0) and 93.6 (83.7-104.6). Similarly, the geometric ratio for the AUC of 1-hydroxymidazolam, the primary metabolite of midazolam, was 105.7 (97.7-114.3); the ratio of C was not equivalent at 116.1 (101.7-132.4), which was outside the CI of 80% to 125%. Multiple doses of oral delafloxacin for 6 days were generally well tolerated.

Implications: Steady-state dosing of delafloxacin produced no significant changes in midazolam pharmacokinetics, except for a small but not clinically relevant change in the C of 1-hydroxymidazolam. ClinicalTrials.gov identifier: NCT02505997.