A Study to Evaluate the Pharmacokinetics, Safety, and Tolerability of Upadacitinib in Pediatric Subjects With Polyarticular Course Juvenile Idiopathic Arthritis

Inclusion Criteria:

• Participant have total body weight of 10 kg or higher at the time of screening.

• Participant diagnosed with pcJIA (rheumatoid factor-positive or rheumatoidfactor-negative polyarticular JIA, extended oligoarticular JIA, or systemic JIA withactive arthritis and without active systemic features) with a history of arthritisaffecting at least 5 joints within the first 6 months of disease (for extendedoligoarticular JIA: <=4 joints within first 6 months of disease and >4 jointsthereafter).

• Participant have 5 or more active joints at the time of screening, defined as thepresence of swollen joints (not due to deformity) or, in the absence of swelling,joints with the limitation of movement (LOM) plus pain on motion and/or tendernesswith palpitation, with LOM present in at least three of the active joints.

• If receiving methotrexate (MTX), have been taking MTX for at least 12 weeksimmediately before and including Study Day 1 on a stable dose of <=20 mg/m2 for atleast 8 weeks before and including Study Day 1; in addition, participants shouldtake either folic acid or folinic acid according to local standard of care.

• If on oral glucocorticosteroids, must have been taking oral glucocorticosteroids ata stable dose (no greater than 10 mg/day or 0.2 mg/kg/day, whatever is lower) for atleast 1 week before and including Study Day 1.

Exclusion Criteria:

• Participant with diagnosis of enthesitis-related arthritis (ERA) or juvenilepsoriatic arthritis (JPSA).

• Participant have prior exposure to JAK inhibitor.