Rituximab 375 mg/sqm weekly for 4 weeks has significant activity in patients with idiopathic thrombocytopenic purpura (ITP). In this setting, different biological and clinical evidence suggests the possible use of lower doses of Rituximab. Twenty-eight adult patients, median age 43 years (range 16–71 years), with previously treated, active and symptomatic ITP were treated prospectively with Rituximab at the fixed dose of 100 mg iv weekly for 4 weeks. Exclusion criteria were positive HIV, HBsAg and pregnancy test, any B-cell lymphoprolipherative disease or other malignancies. Response assessment was evaluated considering the rate of overall and complete responses (OR = platelet count ≥ 50 x 109/L; CR= platelet count ≥ 100 x 109/L and discontinuation of steroid therapy, if present), the time to response (TTR; time necessary to reach a platelet count ≥ 50 x 109/L), the time to complete response (TCR; time necessary to reach a platelet count ≥ 100 x 109/L) and the duration of response. B-cell count and pharmacokinetics (PK) were monitored and related with clinical outcome. Stepwise logistic regression was used to assess whether response was associated with age, gender, diagnosis-Rituximab interval and basal CD20+ve lymphocytes. Results were considered statistical significant when P ≤ 0.05. All patients completed the therapeutic program receiving the four infusions of Rituximab as scheduled, none experiencing short term toxicity. All patients achieved B-cell depletion. OR and CR were achieved in 21/28 (75%) and 12/28 (43%) patients, respectively. CR rate was associated with younger age (OR=0.92 CI95%[0.85;0.99]). The median TTR and TCR were 31 and 44 days, significantly longer then those observed with standard dose in patients with similar characteristics (Haematologica 2003;88:538). After a median follow-up of 11 months (range 3–18), 7/21 (33%) patients relapsed, and 3 needed further treatments. PK data showed a concentration time-course profile of Rituximab that was super-imposable, once corrected for the difference in the dose, to that observed previously in patients treated with standard dose, diseases with a median value of 4.1 micrograms/milliliter (range 0–11.9), 12 weeks after the start of treatment. In patients with ITP, low dose Rituximab led to short and mid-term response rates similar to standard dose but with slower timing of response.
2007, The American Society of Hematolog
