OBJECTIVE: Studies comparing 500 mg rituximab and 1,000 mg rituximab doses in @entity309 have yielded conflicting data on clinical outcomes, but in all of these studies a subgroup of @entity1 has had excellent responses at the lower dose. Historically, it was considered that rituximab uniformly depleted B cells at both doses. Using highly sensitive assays, we have shown that B cell depletion is variable and predictive of clinical response. Using the same techniques, we undertook the present study to test the hypothesis that the level of B cell depletion, rather than the rituximab dose, determines clinical response. METHODS: Nineteen @entity1 were treated with two 500-mg infusions of rituximab, and 61 @entity1 were treated with two 1,000-mg infusions of rituximab. Highly sensitive flow cytometry was performed at 0, 2, 6, 14, and 26 weeks. European League Against @entity627 (EULAR) response rates at 6 months were compared between @entity1 with and those without complete depletion at each dose. RESULTS: The median B cell count was numerically higher at all time points following therapy in the 500 mg rituximab group. Twenty-five percent of @entity1 in the 500 mg rituximab group had complete depletion at 2 weeks, compared with 49% of those in the 1,000 mg rituximab group. Complete depletion at 2 weeks after treatment with 500 mg rituximab was associated with lower baseline preplasma cell counts (P = 0.047). Most @entity1 responded after either dose, but response was related to B cell depletion. Notably, in the 500 mg rituximab group all @entity1 with complete depletion had a EULAR good response (P = 0.011). CONCLUSION: This pilot study suggests that the degree of B cell depletion, rather than the dose of rituximab, determines clinical response. It may be possible to predict which @entity1 will respond to lower-dose rituximab, and this may allow more cost-effective treatment.

Reduced-dose rituximab in XXXX : efficacy depends on degree of B cell depletion.

@entity1 :: ('9606', 'Species') :: ['patients'] @entity627 :: ('MESH:D012216', 'Disease') :: ['Rheumatism'] @entity309 :: ('MESH:D001172', 'Disease') :: ['rheumatoid arthritis']
@entity309 :: (MESH:D001172,Disease) :: ['rheumatoid arthritis']
