The role of rituximab, a chimeric monoclonal antibody directed against the CD20 antigen, in the treatment of patients with chronic idiopathic thrombocytopenic purpura (ITP) has not been determined. The effectiveness and side effects of this therapeutic modality were investigated in a cohort of 25 individuals with chronic ITP. All patients had ITP that had been resistant to between 2 and 5 different therapeutic regimens, including 8 patients who had already failed splenectomy. Patients were scheduled to receive intravenous rituximab at the dose of 375 mg/m 2 once weekly for 4 weeks. Rituximab infusion-related side effects were observed in 18 patients, but were of modest intensity and did not require discontinuation of treatment. A complete response (platelet count greater than 100 ؋ 10 9 /L) was observed in 5 cases, a partial response (platelet count between 50 and 100 ؋ 10 9 /L) in 5 cases, and a minor response (platelet count below 50 ؋ 10 9 /L, with no need for continued treatment) in 3 cases, with an overall response rate of 52%. In 7 cases, responses were sustained (6 months or longer). In 2 patients with relapsed disease, repeat challenge with rituximab induced a new response. In patients with a complete or partial response, a significant rise in platelet concentrations was observed early during the course of treatment, usually 1 week after the first rituximab infusion. No clinical or laboratory parameter was found to predict treatment outcome, although there was a suggestion that women and younger patients have a better chance of response. In conclusion, rituximab therapy has a limited but valuable effect in patients with chronic ITP. In view of its mild toxicity and the lack of effective alternative treatments, its use in the setting of chronic refractory ITP is warranted. (Blood. 2001; 98:952-957)

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