Objective Children are more likely to experience early B-cell repopulation (i.e., 1 month apart, were used to calculate the half-life and predict future rituximab serum concentrations based on the exponential decay principle. Predicted future levels were compared to actual follow-up measurements (i.e., absolute error). Results Ten participants (7 females, median age 14.0 years) with ANCA-associated vasculitis (n=4), neuroinflammatory disease (n=4), or childhood-onset SLE (n=2) contributed 40 samples. The median rituximab half-life was 2.6 weeks (range 1.8–3.5), and the median absolute error was 0.12 μg/mL (IQR -0.02 – 0.26), representing a slight overestimation of the predictions. The minimum required rituximab concentration to maintain B-cell depletion (0.55 μg/mL) was reached at 22.2 weeks (median; range 13.3-28.8). B-cell repopulation was observed in 5 participants at concentrations ≤0.3 μg/mL. One participant had positive anti-drug antibodies (half-life 1.8 weeks). Conclusion This proof-of-concept study demonstrates that rituximab serum concentration measurements can predict future drug concentrations that are associated with early B-cell repopulation. This approach may enable earlier rituximab redosing to prevent increased disease activity associated with B-cell repopulation.
Alsulami et al. (Sun,) studied this question.