Background and importance Biosimilar drugs should have proven clinical efficacy comparable with the referring brand to obtain authorisation from medicine regulatory agencies. Nevertheless, the effectiveness and safety of off-label uses are not always proved.

Aim and objectives The endpoint of this study was to evaluate the early effectiveness and safety of biosimilar rituximab compared with the referring brand for an off-label use: glomerular inflammatory renal disease.

Material and methods This was an observational retrospective study in patients with glomerular inflammatory disease treated with rituximab (1 g single dose or 1 g two doses). Patients receiving rituximab for the first time between March 2018 and March 2019 were included. Information on patient demographics, underlying disease and associated treatment was collected from the patient medical records. Laboratory data including creatinine, proteinuria, leucocyte and lymphocyte count were collected before (0–60 previous days) and after (0–60 days after) administration of rituximab.

Results Six patients (mean age 59 years (26–74); 50% women) with baseline 6.52±2.00×10⁹/L leucocyte count, 2.28±1.10×10⁹/L lymphocyte count, 1.63±1.04 mg/dL creatinine and 6.84±3.36 g/24 hours proteinuria were treated with biosimilar rituximab. Thirteen patients (mean age 58 years (25–81); 30% women) with baseline 9.80±4.62×10⁹/L leucocyte count, 1.92±1.13×10⁹/L lymphocyte count, 1.61±0.85 mg/dL creatinine and 5.81±4.55 g/24 hours proteinuria were treated with brand rituximab. After rituximab administration, these values were 6.13±1.94×10⁹/L leucocyte count, 1.30±0.59×10⁹/L lymphocyte count, 1.16±1.19 mg/dL creatinine, 3.29±0.58 g/24 hours and proteinuria for the biosimilar group, and 8.77±3.78×10⁹/L leucocyte count, 1.67±1.13×10⁹/L lymphocyte count, 1.56±1.19 mg/dL creatinine and 3.36±2.20 g/24 hours proteinuria for the brand group. After rituximab administration, CD19+ lymphocytes become negative in both groups (5/5 for the biosimilar group; 6/6 for the brand group). There were two total remissions, one partial remission and three non-responses with the biosimilar rituximab, and one total remission, five partial remissions and seven non-responses with the brand rituximab. Biosimilar rituximab was well tolerated in 6/6 patients and no infections developed. Brand rituximab was well tolerated in 11/13 patients and 4/13 patients showed an infectious episode. No significant differences were observed for the treatment response between the two groups.

Conclusion and relevance Biosimilar rituximab showed an effectiveness and safety profile similar to brand rituximab. Nevertheless, the small sample limits the statistical power and suggests a larger study is required to confirm these results, which we are currently working on.

References and/or acknowledgements No conflict of interest.