Is rituximab sub‐optimally dosed in indolent B cell lymphoma?

Rituximab pharmacokinetics are affected by gender, age and weight and can affect outcomes in aggressive B cell lymphoma. Less is known about the pharmacokinetics of rituximab in indolent B cell lymphoma ( iNHL ). We analysed the effects of gender, age, weight and body surface area on the outcomes of 303 patients treated with first line rituximab‐based regimens for iNHL . The patients were divided into 3 treatment cohorts: rituximab only, rituximab + chemotherapy (R‐ CTX ) and R‐ CTX followed by rituximab maintenance; furthermore, each cohort was subdivided as follicular ( FL ) or non‐ FL , based on histology. Older males and patients with higher weight had worse outcomes when treated with R‐ CTX , probably due to faster rituximab clearance. Our results concur with studies of R‐ CTX for DLBCL . As this effect was not observed in patients treated with rituximab alone or R‐ CTX followed by rituximab maintenance, we hypothesize that higher rituximab levels reached with weekly rituximab and/or prolonged exposure achieved with maintenance therapy exceed the therapeutic threshold, even with faster clearance, which nullifies the negative effect of higher weight and male gender. In conclusion, under current practices, a subset of patients with iNHL , i.e., FL treated with R‐ CTX , may be sub‐optimally dosed with rituximab.