Use of B-cell biomarkers can help reduce rituximab dosing for patients with Neuromyelitis Optica Spectrum Disorder (NMOSD) without compromising efficacy, neurologists in NSW have shown.
Presenting their findings at PACTRIMS 2018 in Sydney, Dr Benjamin Trewin and colleagues at the RPAH Neuroimmunology Clinic noted that rituximab has become the standard of care in NMOSD following case series showing it is associated with an almost 100% reduction in relapse rates.
However the standard rituximab dosing schedule used in rheumatology clinics of 2mg initially followed by redosing at six monthly intervals may not be ideal for patients with NMOSD, they postulated.
Reporting on experience from the RPAH clinic between 2013 and 2018, they described an individualised rituximab regimen for NMOSD patients, with dosing triggered when levels of the biomarker Switched Memory B-Cells (SMB) reached a threshold of 0.0005 (x109). Most patients were concurrently treated with mycophenolate or azathioprine.
Data from 24 patients with NMOSD showed that 74% were Aquaporin-4 antibody positive, 13% MOG antibody positive and 17% had a positive family history.
Among the 18 patients who were re-dosed with rituximab the mean interval between doses was 10.5 months and the mean interval between SMB cell measurement was 4.5 months. The average SMB count that triggered a re-dose was 0.0006. Of the three patients who experienced relapses following rituximab treatment, two had SMB counts in excess of the redosing threshold.
Adverse events with rituximab, including lymphopaenia and infections, were in line with expectations from previous literature.
Dr Trewin and colleagues said it was difficult to determine the true reduction in relapse rates with rituximab because there was no control group, but the pre and post assessment data for each NMOSD patient provided “compelling evidence” of benefit in line with previous cohort results.
And due to the infrequency of relapses it was similarly difficult to assess the usefulness of SMB-cells as an indicator of re-dosing, but the three cases again showed that this was in line with predictions, they added.
Another major benefit of the individualised dosing regimen was that it reduced the number of infusions for patients and also produced considerable costs savings, given that a single rituximab 500mg vial cost $1563, the researchers noted.
Direct savings of $131,268 were achieved through using 84 fewer vials of rituximab than a standard dosing schedule, with additional savings from reduced infusion requirements, they said.
“This study provides further real world data to support individualised, safe and effective treatment of MNOSD with lower doses of rituximab,” they concluded.