Assuming the concentration of BLyS-RCT-18 complex and the IgM/IgG ratio are surrogate biomarkers for clinical effects of RCT-18 , the dose-response relationship suggests 180-540mg are pharmacodynamically effective doses in RCT-18 for RA patients , but the effect profile of 540mg RCT-18 on IgM is similar to that of atacicept at pharmacodynamically effective but clinically ineffective doses .