Complement Inhibitor Clinical Trial Landscape

The complement system: one pathway, a dozen indications

The complement system is a network of ~50 proteins that serve as one of the body's first lines of defense against pathogens — but when dysregulated, it becomes a driver of tissue destruction. The cascade activates through three pathways (classical, lectin, alternative), all converging on C3 and then the terminal complex (C5a + C5b-9/MAC). Each node is a druggable target, and the right target depends on which part of the cascade is driving disease in each indication.

The complement space has matured from a single approved drug (eculizumab, 2007) to a multi-mechanism, multi-indication landscape with 8+ approved drugs and dozens of Phase 2/3 trials across rare hematology, nephrology, neurology, and ophthalmology. Competitive intelligence in this space requires tracking both drug-specific programs and indication-specific activity simultaneously.

Approved complement inhibitors — the competitive benchmark

IgA nephropathy: the newest high-stakes indication for complement

IgA nephropathy has emerged as perhaps the most competitive new indication for complement inhibitors in 2025–2026. The pathogenesis involves Gd-IgA1-containing immune complexes depositing in the kidney mesangium, where they activate the complement alternative pathway and lectin pathway, driving inflammation and progressive GFR loss. Both Factor B (amplification loop) and C5 (terminal effector) are relevant targets, and two different complement approaches are now in Phase 3 simultaneously:

• Iptacopan (Novartis, Factor B) — APPLAUSE-IgAN: Phase 3 trial testing iptacopan as add-on to standard of care in IgAN. Phase 2 data showed 38% reduction in proteinuria. Targets the alternative pathway amplification loop specifically, which is particularly overactivated in IgAN
• Ravulizumab (Alexion, C5) — Phase 3 IgAN adult: Blocks the terminal complement component C5, preventing both C5a (inflammatory) and MAC (cytotoxic) formation. The Phase 3 program is currently recruiting adults
• Ravulizumab — Phase 3 IgAN pediatric: Separate pediatric Phase 3 program also recruiting — a strategic move to establish label in the age group where lifetime kidney preservation is most valuable

The competitive question for IgAN specifically: does blocking the amplification loop (Factor B, iptacopan) provide superior nephroprotection compared to blocking the terminal effector (C5, ravulizumab)? Or does proximal pathway blockade (iptacopan) prevent more upstream damage that terminal C5 blockade cannot? Phase 3 readouts are expected 2026–2027 and will define the complement sub-strategy for IgAN.

Active Phase 3 complement inhibitor trials — 2026

Iptacopan: the oral Factor B inhibitor expanding beyond PNH

Iptacopan (Fabhalta) received FDA and EMA approval in 2023 as the first oral monotherapy for PNH — a significant commercial win for Novartis, as it displaced intravenous C5 inhibitors for many patients. But the more interesting story is what Novartis is doing with iptacopan across other complement-driven indications:

• IgA nephropathy — APPLAUSE-IgAN Phase 3 (add-on to standard of care); mechanism rationale is strong because IgAN drives heavy alternative pathway amplification
• Generalized myasthenia gravis — Phase 3 now recruiting; complements the approved C5 inhibitors (eculizumab and ravulizumab) in gMG with a potentially oral option
• ANCA-associated vasculitis — Phase 2 study testing iptacopan in AAV (where avacopan is approved for C5aR1 blockade); if successful, opens question of whether upstream Factor B inhibition is superior to terminal C5aR1 blockade
• C3 glomerulopathy (C3G) — complementary indication to PNH and IgAN; Novartis has disclosed interest in expanding in glomerular disease

Iptacopan's oral availability is a major competitive advantage vs. IV/SC biologics. If Phase 3 IgAN data is positive, it potentially creates a scenario where the same drug can be used in PNH, IgAN, and gMG — a cross-indication strategy reminiscent of rituximab.

The PNH landscape: from one drug to a multi-mechanism competition

PNH began as a single-drug category (eculizumab, approved 2007) and has evolved into a complex multi-mechanism competitive space in 2026:

• Terminal C5 inhibition — eculizumab (every 2 weeks IV) vs. ravulizumab (every 8 weeks IV) vs. pozelimab (IV but high-affinity binding to capture complement spikes); all in the same mechanism class with differentiation on dosing frequency
• Proximal complement inhibition (oral) — iptacopan (Factor B, oral twice daily) vs. danicopan (Factor D, oral three times daily); iptacopan won the oral PNH race; danicopan approved only as add-on in the EVH subgroup
• C3 inhibition — pegcetacoplan (SC every 3–4 days); broader pathway blockade but SC administration burden
• RNA-based C5 reduction — cemdisiran (RNAi, targets hepatic C5 synthesis) combined with pozelimab (to capture residual circulating C5); the Regeneron combination strategy avoids the complement spike escape issue seen with C5 mAbs alone

Who monitors complement inhibitor trials

• Rare disease BD teams at pharma (Novartis, Alexion/AstraZeneca, Apellis, Regeneron) — tracking competitor entries across PNH, IgAN, gMG, ANCA vasculitis, and geographic atrophy
• Nephrology and hematology-focused investors — monitoring Phase 3 readouts and enrollment completions across a half-dozen complement indications simultaneously
• Complement biotech founders and scientific advisors — identifying white space and mechanism gaps (e.g., lectin pathway inhibition remains relatively underdeveloped)
• CROs specializing in rare disease — tracking sponsor program activity and site-selection signals in PNH, IgAN, and aHUS
• Medical affairs teams — monitoring competitive entries in approved indications (e.g., new programs in gMG competing with ravulizumab and eculizumab)

Related Pages

• IgA nephropathy clinical trials — dedicated tracker for IgAN, including complement, APRIL/BAFF, and endothelin programs
• Chronic kidney disease clinical trials — broader CKD pipeline including SGLT2, APOL1, and GLP-1 programs
• Multiple myeloma clinical trials — CD38 and BCMA programs that share key patient populations with hematology complement indications
• BTK inhibitor clinical trials — B-cell signaling pathway, mechanistically upstream of some complement-driving disease processes
• Pharma pipeline tracker — full sponsor-level pipeline view including Novartis, Alexion, Apellis, and Regeneron

Frequently asked questions