Pharmacokinetics and Pharmacodynamics of Biologic Drugs in Obese Patients With Arthritis

Inclusion Criteria * Diagnosis of Rheumatoid Arthritis (RA) according to the 2010 American College of Rheumatology Classification Criteria (patients greater than or equal to 16 years of age at screening) * Diagnosis of Juvenile Idiopathic Arthritis (JIA) according to the International League Against Rheumatism Classification Criteria (children less than 16 years of age at screening) * Initiating treatment with etanercept as standard of care by a patient's primary rheumatologist * Obese at baseline, defined as a body mass index (BMI) greater than or equal to 30 kg/m2 in subjects greater than or equal to 18 years of age, and a BMI greater than or equal to 95th percentile for age and sex in subjects less than18 years of age * Active disease at screening, defined as a DAS28 \> 3.2 in adults and JADAS27 \> 3.8 in children * Patients using oral corticosteroids (\<10 mg) or DMARDs must be on a stable dose for at least 4 weeks prior to screening Exclusion Criteria * Receipt of any investigational medical product within the past 12 months * Positive urine pregnancy test at screening or planned pregnancy during the study period * Prior exposure to etanercept or any other biologic agent within 5 drug half-lives * Contraindication to etanercept (e.g., allergy, current or chronic infection \[positive tuberculosis screening test, positive hepatitis B surface antigen, positive hepatitis C antibody\]) * Personal history of ever having malignancy, lymphoproliferative disease, or demyelinat…