LIVERPOOL, ENGLAND — Increasing experience with rituximab in patients with rheumatoid arthritis is showing that infection rates remain stable with repeat courses of treatment, Dr. Shouvik Dass has reported.
All patients who participated in the pivotal trials of rituximab in RA were entitled to enter into an open-label phase in which they can receive further courses of treatment, depending on disease activity.
As of September 2006, 1,053 RA patients had received rituximab. There are now 2,438 patient-years of exposure, with 400 patients having had three courses and 142 having had four, said Dr. Dass of the academic unit of musculoskeletal disease, University of Leeds (England).
Both adverse events and serious adverse events have decreased with each course. A total of 702 patients (67%) reported any infection; most were upper respiratory tract and urinary tract infections.
“Importantly, in the context of biologic therapy, there have been no opportunistic infections or cases of viral reactivation or tuberculosis,” Dr. Dass said at the annual meeting of the British Society for Rheumatology. Serious adverse event rates also are low and not changing through four courses, he said.
In all, 36 malignancies have been seen in 32 patients, four of which had fatal outcomes. “RA carries its own risk for malignancy, particularly lymphoproliferative disease, but there have been no lymphoproliferative malignancies and no evidence has emerged of increasing malignancies with repeated courses of treatment,” he said.
The B-cell depletion that occurs with rituximab therapy also raises concerns about the levels of immunoglobulins, secreted by plasma cells. Up to one-quarter of patients have low IgM by their fourth course of treatment. About 4%–5% have low IgG.
To determine if this decrease in immunoglobulin levels is clinically significant, infection rates were analyzed according to IgM and IgG levels. For patients with normal IgM, the serious infection rate was 4.9 per 100 patient-years, and for those with low IgM it was 6.4 per 100 patient years, a difference that was not statistically significant.
For IgG, the rate of all infections was 109 per 100 patient-years in patients with the lowest levels of IgG, and 63 per 100 patient years among those who had the highest levels, a significant difference, Dr. Dass said.
The rates of serious infections, however, were similar, with 6.8 per 100 patient-years in the lowest IgG group and 5 per 100 patient-years in the highest IgG group.
These findings are consistent with earlier data. “We need to see if there is any further association between changes in immunoglobulins and risk of infection and whether in the future that will affect our clinical practice,” he said.
Dr. Dass declared no conflicts.