A Phase I Study to Evaluate the Safety, Tolerability, and Pharmacokinetics of Fenebrutinib and Effect on the QT/QTc Interval in Healthy Participants.

Fenebrutinib is a Bruton's tyrosine kinase inhibitor under investigation for the treatment of multiple sclerosis. The goal of this study was to investigate the effect of fenebrutinib on cardiac repolarization (QT interval) as well as its safety, tolerability, and pharmacokinetics in healthy participants. Part A was a randomized, double-blind, placebo-controlled, single-ascending dose study of therapeutic (400 mg) and supratherapeutic (700 mg) doses of fenebrutinib. Part B was a randomized, double-blind, single-dose, four-way crossover study that included both therapeutic and supratherapeutic fenebrutinib doses, a positive control (moxifloxacin 400 mg), and placebo. The QT interval was corrected for heart rate using the Fridericia formula (QTcF). Part A (n = 16) showed that both doses were well tolerated, with no serious adverse events (AEs), AEs of special interest, or Grade ≥ 2 AEs. In Part B (n = 85), all upper bounds (UBs) of one-sided 95% confidence intervals (CIs) for the least squares mean placebo-adjusted ΔQTcF (ΔΔQTcF) values were < 10 ms; maximum observed values were 5.3 and 8.2 ms at 1 h after the therapeutic and supratherapeutic doses, respectively. All predefined timepoints after moxifloxacin administration had a 99% CI lower bound of ΔΔQTcF of > 5 ms, which confirmed assay sensitivity. In the regression analysis, UBs of one-sided 95% CIs for ΔΔQTcF at the maximum concentration of fenebrutinib were < 10 ms: 4.4 and 7.8 ms with the therapeutic and supratherapeutic doses, respectively. Overall, both doses of fenebrutinib had no clinically meaningful impact on QT interval and were well tolerated, supporting fenebrutinib's favorable safety profile and continued clinical development.