Comparison of nadir serum concentrations in the extended dosing therapy of natalizumab between American and Japanese multiple sclerosis patients

Natalizumab, a humanized monoclonal antibody against very late antigen-4 (VLA-4), inhibits the transmigration of immune cells across the bloodbrain barrier into the central nervous system (CNS). However, progressive multifocal leukoencephalopathy (PML) is caused following natalizumab treatment in patients with relapsing remitting multiple sclerosis (RRMS). The reason for higher PML prevalence in patients treated with natalizumab in Europe than those in the USA patients may not be the more frequent use of cytotoxic medications in Europe, but may be the lower body weight (BW) of European patients and higher nadir serum concentrations of natalizumab. We recommended BW-based natalizumab therapy in RRMS patients because a linear relation exists between serum concentrations and BW (50 110 kg) (y1⁄4 0.5363xþ 75.71, R1⁄4 0.846). Recently, extended interval dosing of natalizumab therapy has been shown.