Rituximab Induces High Response Rate and Prolonged Remission in Chronic Idiopathic Thrombocytopenic Purpura (ITP): A Retrospective Analysis

BACKGROUND: Rituximab is a chimeric monoclonal antibody targeting CD 20+ B lymphocytes (Rastetter et al, 2004). Combination of rituximab with conventional chemotherapeutic agents has become the mainstay of treatment for B-cell Non-Hodgkin’s Lymphomas. The role of rituximab in treatment of immune mediated disorders is currently under investigation. Earlier studies have reported significant responses to rituximab in chronic idiopathic thrombocytopenic purpura patients, who are refractory to steroids and in some cases to splenectomy. (Cooper et al, 2004). METHODS: We retrospectively reviewed charts of 15 patients who received rituximab treatment for chronic ITP. All patients had clinical features consistent with chronic ITP and no other etiology was discovered to cause thrombocytopenia; diagnosis of ITP was confirmed by bone marrow examination in 8 patients. Previous treatments for patients in our series included: prednisone (80%), splenectomy (53%), Rho D immune globulin (40%), IV immunoglobulin (33%), danazole (27%), and vincristine (20%). Rituximab dose was 325mg/m2 for all patients, although the number of treatments varied between patients (Table 1). Complete or partial responses to therapy were defined as follows: Platelet count ≥ 150x10(9)/L at 12 weeks following first infusion was a complete response (CR). Platelet count 50–149x10(9)/L at 12 weeks following first infusion was a partial response (PR). Platelet count < 50x10(9)/L was defined as no response (NR). Response at the 12 week interval was not possible in 2 patients; therefore response was defined at the 8 week interval (Table 1). RESULTS: Patient demographics consist of 5:10 male to female ratio with mean age=49.7, median age= 46 and age range=19–83. 10 patients attained a complete response, 3 patients attained a partial response, and 2 patients failed to show any response to treatment. It was possible to follow 12 patients in our series for a sustained duration of rituximab response; 9 patients (75%) showed a response of >6 months in this group. The most significant factor associated with response to rituximab was age, independent of all other variables when logistic regression analysis was utilized (p=0.003, α=0.05, df=1). Additionally, bivariate analysis was significant for age and number of days lapsed (following first infusion) until platelets increase ≥ 100x10(9)/L and was independent of baseline platelet count (p=0.047, α=0.05, df=1). CONCLUSION: Rituximab has shown significant activity in our series of ITP patients, with an overall response rate of 93%. Our results indicate a direct relationship between younger age and response. The availability of this agent provides another treatment option for chronic ITP, short of splenectomy. Guidelines for ITP may need further modification in view of the promising results with rituximab therapy.