NEW YORK (Reuters Health) Jan 25 - The clinical efficacy of rituximab in rheumatoid arthritis (RA) depends on the degree of B cell depletion rather than the dose of rituximab, researchers from the UK report in the December 28th Arthritis & Rheumatism online.
"It may be possible to tailor the dose of rituximab in RA," Dr. Dennis McGonagle from the University of Leeds, Chapel Allerton Hospital, Leeds, told Reuters Health in an email.
"Whether low dose tailoring will diminish the fall in immunoglobulins or whether it may avert side effects remains to be seen."
Dr. McGonagle and colleagues investigated the impact of B cell depletion and rituximab dose on the clinical response in 94 patients with rheumatoid arthritis. Twenty-one patients were treated with two infusions of 500 mg rituximab, and 73 were treated with two infusions of 1000 mg rituximab.
Disease activity improved in both treatment groups between baseline and 6 months.
The clinical response in both groups was related to the degree of B cell depletion, which was generally higher after the 1000 mg doses than after the 500 mg doses.
When complete B cell depletion was achieved, there was no difference in the clinical response rate between the 1000 mg and 500 mg doses. All four patients in the 500 mg group that achieved complete B cell depletion showed a good response, and all five patients that had no response had incomplete B cell depletion.
Similarly, clinical non-response in the 1000 mg group was significantly associated with incomplete B cell depletion. Twelve of 21 patients with a good response had complete B cell depletion, whereas 12 of 16 patients with no response had incomplete B cell depletion.
"Further longitudinal work in bigger cohorts formally showing that the responses to RTX 500 can predict good efficacy is needed," Dr. McGonagle said.
"Clinically several studies including DANCER and MIRROR suggest that lower doses work in some cases," Dr. McGonagle continued. He added that he personally believes that "a trial dose of 500 X 2 is not an unreasonable strategy."
Arthritis Rheum. Posted online December 28, 2011. Abstract