Risk factors for side effects during first infusion of rituximab-definition of a low risk group.

Side effects from the first infusion of the monoclonal anti-CD20 antibody, rituximab, 375 mg/m2 was documented in 47 treatments (37 patients) and correlated to tumour mass and interval to previous cytostatic treatment. A significant correlation was found with less side effects in patients with a low tumour mass and/or if chemotherapy was recently administered. It is difficult to differ between these two parameters as they covariate, i.e. the majority of patients without or with a minimal tumour burden were recently treated with cytostatics. The reason why these patients have no or minimal side effects may be due to low numbers of CD20 positive cells in the circulation. The finding of a low-risk group for side effects from the first infusion of rituximab; has practical clinical implications, for example, hospitalization can be avoided. Concerning side effects, it may be an advantage to give rituximab after the introduction of successful chemotherapy.