Natalizumab for use in a method to treat an inflammatory or autoimmune disease, wherein said method comprises: (a) administering a first dose of natalizumab during a first period of administration； (b) control the amount of bivalent natalizumab in the patient's plasma or serum during the first period of administration； (c) determine a second dose of natalizumab based on the level of bivalent natalizumab observed； and (d) administer a second dose of natalizumab during a second period of administration； where if the control shows that the amount of bivalent natalizumab in the patient's plasma or serum remains above a predetermined level during the first period of administration, then the second dose of natalizumab administered during the second period of administration is designed to achieve reduction of natalizumab level during the second period of administration below the predetermined level for at least a portion of the second period of administration； where the second dose improves the safety and / or efficacy of the treatment during the second period of administration； and where the predetermined level of bivalent natalizumab in the patient's plasma or serum during the first period of administration is selected from 0.1 μg / ml, 0.5 μg / ml and 1 μg / ml.Natalizumab para su uso en un método para tratar una enfermedad inflamatoria o autoinmune, donde dicho método comprende: (a) administrar una primera dosis de natalizumab durante un primer período de administración； (b) controlar la cantidad de natalizumab bivalente en el plasma o suero del paciente durante el primer período de administración； (c) determinar una segunda dosis de natalizumab en base al nivel de natalizumab bivalente observado； y (d) administrar una segunda dosis de natalizumab durante un segundo período de administración； donde si el control muestra que la cantidad de natalizumab bivalente en el plasma o suero del paciente permanece por encima de un nivel predeterminado durante el primer período de
