Dosing for biologic agents such as adalimumab and etanercept in children do not account for the physiologic changes resulting from obesity. These changes may result in a high inflammatory state and can affect how the medications are handled by the body, potentially leading to treatment failure and worsening arthritis. In this proposal, we will use advanced pharmacokinetic and pharmacodynamic modeling to determine how obesity impacts treatment with adalimumab etanercept in children with juvenile idiopathic arthritis, and use the model to optimize dosing to reduce arthritis disease activity.