Successful Transition from Eculizumab to Iptacopan in a Pediatric Case of C3 Glomerulopathy Refractory to Immunosuppressive Therapy

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Successful Transition from Eculizumab to Iptacopan in a Pediatric Case of C3 Glomerulopathy Refractory to Immunosuppressive Therapy

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Co-author 1

HISASHI KANEDA pediat_kaneda@hosp.komatsu.ishikawa.jp Komatsu Municipal Hospital Pediatrics Komatsu Japan *

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Introduction

C3 glomerulopathy (C3G) is a subtype of membranoproliferative glomerulonephritis characterized by uncontrolled activation of the complement alternative pathway. Conventional immunosuppressive therapies show limited efficacy, and up to 50% of patients progress to end-stage kidney disease within 10 years. Recently, complement-targeted agents such as eculizumab and iptacopan have become available.

Methods

An 18-year-old boy developed asymptomatic hematuria at age 10. Serum C3 levels remained persistently low (<4 mg/dL). Proteinuria gradually increased, and renal biopsy revealed a membranoproliferative pattern with C3-dominant deposits. C3 nephritic factor was positive, and plasma sC5b-9 was elevated. Anti–factor H antibody and complement gene analysis were negative. Treatment with corticosteroids, RAAS inhibitors, and mycophenolate mofetil was ineffective. Eculizumab was initiated at age 15 and continued for 4.5 years, resulting in reduced sC5b-9 but persistent hypocomplementemia and proteinuria. In August 2025, therapy was switched to iptacopan, a factor B inhibitor.

Results

After three months, his urine protein-to-creatinine ratio decreased from 3.0 to 2.0, and eGFR improved from 87 to 100 mL/min/1.73m². No serious infections or adverse events occurred.

Conclusion

In this case, downstream complement blockade with eculizumab provided limited efficacy in C3G with upstream alternative pathway dysregulation. In contrast, upstream factor B inhibition with iptacopan improved renal parameters, suggesting that targeting the alternative pathway upstream may represent a more pathophysiology-based treatment strategy for similar patients.

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