In general, rituximab has an acceptable toxicity profile. However, as the drug has been used more widely, new side effects have been identified that warranted a modification of the package insert. Approximately 70 serious infusion-related events have been reported, with 8 fatalities out of an estimated14,000 patients treated. Death was associated with bronchospasm, hypotension, and severe respiratory distress, with no clear predisposing factors.

In addition, a small number of patients treated with rituximab at a time when they had bulky disease and circulating tumor cells developed thrombocytopenia, a rapid decrease in tumor load, and a number of electrolyte abnormalities consistent with tumor lysis, but not clearly a tumor lysis syndrome (Byrd et al, abstract #432; Byrd et al: J Clin Oncol, vol 17, 1999 [in press]). In general, tumor lysis in indolent disorders cannot be readily predicted (Cheson et al: J Clin Oncol 16:2313-2320, 1998) or prevented. Rapid intervention is most important for a successful outcome.