GS-829845 is a major, active metabolite of Filgotinib (JAK1 preferential inhibitor but is approximately 10-fold less potent than the parent and with a longer half-life[1][2].
[1]. Amy Meng, et al. Exposure-response relationships for the efficacy and safety of filgotinib and its metabolite GS-829845 in subjects with rheumatoid arthritis based on phase 2 and phase 3 studies. Br J Clin Pharmacol. 2022 Jul;88(7):3211-3221.
[2]. Chia-Hsiang Hsueh, et al. Evaluation of the potential drug interactions mediated through P-gp, OCT2, and MATE1/2K with filgotinib in healt subjects. Clin Transl Sci. 2022 Feb;15(2):361-370.