Filgotinib in rheumatoid arthritis.

Preclinical studies demonstrate preferential inhibition of JAK1 and a promising pharmacokinetic profile with few drug-drug interactions. Increase in hemoglobin in line with preferential inhibition of JAK1 over JAK2 is seen in early-phase clinical trials. A phase III program demonstrates efficacy in several disease stages, numerically higher with 200 mg versus 100 mg daily. In the overall RA population such dose-related effect is not observed for safety except for herpes zoster and increases in lipids and creatine phosphokinase. This reassuring safety profile is to be confirmed in future practice. It also needs to be unraveled if JAK1 preferential inhibition plays a key role in this safety profile.