ObjectiveB‐cell depletion using the anti‐CD20 monoclonal antibody rituximab is a cornerstone in the therapeutic concept of multiple autoimmune diseases. B‐cell depletion is associated with a higher risk for severe infections, and the time span of B‐cell repopulation differs greatly between individuals. Data on factors influencing B‐cell repopulation kinetics are limited. This study aims to identify patient‐specific and therapy‐associated covariates that modulate B‐cell repopulation.MethodsThis single‐center retrospective observational study presents data of 839 subjects receiving 2,017 courses of rituximab for autoimmune diseases. Assessed covariates are patient‐specific factors (sex, age, kidney function, and underlying disease) and co‐immunosuppression with common agents (azathioprine, cyclosporine A, cyclophosphamide, hydroxychloroquine, methotrexate, mycophenolate mofetil, tacrolimus, and corticosteroids). The primary end point is the time to B‐cell repopulation (≥5/μl). The secondary end point is the time to B‐cell reconstitution (≥50/μl). Multivariate time‐to‐event analysis and logistic regression models were applied to estimate the influence of covariates.ResultsAge over 60 years (hazard ratio [HR] 0.71 for repopulation, P = 0.008), impaired kidney function (HR 0.72, P = 0.001), antineutrophil cytoplasmic antibody‐associated vasculitis (HR 0.61, P < 0.001), solid organ transplantation (HR 0.4, P < 0.001), and co‐immunosuppression with corticosteroids (HR 0.64, P < 0.001) or azathioprine (HR 0.49, P < 0.001) were associated with impaired B‐cell repopulation and reconstitution. Effects of corticosteroids (P = 0.043) and azathioprine (P = 0.025) were dose dependent.ConclusionProlonged rituximab dosing intervals may be effective to achieve B‐cell depletion and reduce risk of infection in advanced age or patients with impaired kidney function. Co‐medication with corticosteroids or azathioprine prolongs B‐cell recovery, which may increase therapeutic effects but also the rate of adverse events.image