Upadacitinib is a Janus kinase 1 inhibitor developed for treatment of moderate 
to severe rheumatoid arthritis (RA) and was recently approved by the US Food and 
Drug Administration for this indication in adults who have had an inadequate 
response or intolerance to methotrexate. Upadacitinib is currently under 
regulatory review by other agencies around the world. Ongoing trials are 
investigating the use of upadacitinib in other inflammatory autoimmune diseases. 
In this article, we review the clinical pharmacokinetic data available to date 
for upadacitinib that supported the clinical development program in RA and 
ultimately regulatory applications for upadacitinib in treatment of patients 
with moderate to severe RA.