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 demyelinating disease * Screening safety labs with a hemoglobin of ≤ 9 g/dL, white blood cell count \<3.0x109L, platelets \<125,000 x109L, AST/ALT more than 2x the upper limit of normal, or creatinine \> 2 mg/dL for adults and \>1 mg/dL for children * Evidence of erosive osteoarthritis on plain films (if available at time of screening), or severe osteoarthritis (defined as any anticipated need for joint replacement within the next year) as judged by the primary rheumatologist * History of any opportunistic infections, or recent severe infection in the 3 months prior to screening (e.g., hepatitis, pneumonia, pyelonephritis, bacteremia) * Heart failure with NYHA classification 3 or more * Severe functional impairment status, defined as HAQ \>2 and CHAQ \>1.75