Filgotinib is a potent, selective Janus kinase‐1 inhibitor being developed to treat chronic inflammatory diseases. This phase 1 study in healthy subjects evaluated the relative bioavailability of filgotinib maleate tablets versus the reference tablet (filgotinib hydrochloride) and effects of food and acid‐reducing agents (ARAs) on the pharmacokinetics of filgotinib and its major metabolite. Noncompartmental pharmacokinetic parameters of filgotinib and its major metabolite were compared between the 2 tablets at 100‐ and 200‐mg doses and with or without food or ARAs. Filgotinib maleate tablets resulted in equivalent plasma exposures (area under concentration‐time curve to infinity [AUC∞] and maximum concentration [Cmax]) of filgotinib and its metabolite as the reference tablet (90%CIs of geometric least‐squares mean ratios were within the prespecified no‐effect boundary of 70% to 143%). Food intake had no effect on filgotinib AUC∞, but a high‐fat meal reduced Cmax by 20%. Coadministration of filgotinib with omeprazole or famotidine had no effect on filgotinib AUC∞, but omeprazole decreased Cmax by 27%. Neither food nor ARAs affected metabolite exposure. Single‐dose filgotinib 100 or 200 mg was well tolerated. This study supports evaluation of filgotinib maleate tablets, administered without regard to food or ARAs, in future clinical studies.

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