Efficacy and safety of rituximab in Japanese patients with acquired thrombotic thrombocytopenic purpura refractory to conventional therapy.

Thrombotic thrombocytopenic purpura (TTP), while rare, is a potentially life-threatening disorder. Plasma exchange (PE) is considered the primary treatment for TTP. In Western countries, rituximab, an anti-CD20 antibody, is recommended with PE for the treatment of refractory/relapsed TTP, and as up-front therapy in newly diagnosed TTP with neurological/cardiac pathology. The present open-label, single-arm, multicenter study evaluated the efficacy and safety of rituximab in Japanese patients with refractory/relapsed TTP. Patients received rituximab 375 mg/m(2) intravenously, once weekly for a total of four treatments, with PE and steroids. Of six evaluable patients in the full analysis set, two met the primary efficacy endpoint (platelet count >150 × 10(9)/L at week 4), yielding a 33.3 % response rate (95 % confidence interval: 4.3-77.7). While the lower confidence limit of the primary efficacy endpoint failed to reach the pre-specified threshold of 30 %, clinically significant recovery of platelet count with discontinuation of PE, increase of ADAMTS13 activity, disappearance of ADAMTS13 inhibitor, and improvement of TTP-associated clinical manifestations were observed after rituximab therapy in all patients. No safety concerns were identified in this study; therefore, rituximab is considered a useful treatment option in Japanese TTP patients who are refractory to conventional therapy. Trial registration JMA-IIA00160.