Therapeutic Comparison of Complement-Pathway Inhibitors for Paroxysmal Nocturnal Hemoglobinuria: A Systematic Review and Network Meta-Analysis

Description

1. Introduction Paroxysmal nocturnal hemoglobinuria (PNH) is a rare, acquired clonal hematopoietic stem cell disorder with significant clinical burden despite its rarity. The disease is characterized by complement-mediated intravascular hemolysis, hemoglobinuria, debilitating fatigue, dyspnea, thrombotic complications, and progressive renal impairment. Some patients present with concurrent bone marrow failure syndrome manifesting as aplastic anemia. The pathophysiology involves acquired somatic mutations in an X-linked gene encoding glycosylphosphatidylinositol (GPI) anchor synthesis, resulting in defective expression of complement regulatory proteins on the surface of blood cells. Without these protective proteins, circulating cells become susceptible to uncontrolled complement activation and destruction. Historically, untreated or inadequately treated PNH carried a dismal prognosis, with 10-year survival rates as low as 50%. The introduction of complement-targeted therapies over the past 15 years has transformed outcomes, improving 10-year survival to over 75%. Current standard therapeutic approaches are primarily focused on inhibiting terminal complement pathway activation through blockade of complement protein C5. This strategy is executed via two principal agents: eculizumab, a humanized monoclonal antibody that prevents C5 cleavage and membrane attack complex formation, which reduces transfusion requirements by more than 50% and thromboembolic events by nearly 70%, and ravulizumab, a long-acting second-generation C5 inhibitor with an extended half-life facilitating less frequent dosing. However, significant therapeutic limitations persist. Eculizumab exhibits breakthrough hemolytic events in 11% to 27% of treated patients due to suboptimal dosing, carries prohibitive treatment burdens with biweekly infusions necessitated by its short half-life, incurs substantial costs, and carries considerable infectious risks requiring mandatory meningococcal vaccination and antimicrobial prophylaxis. Ravulizumab offers apparent advantages through a 3- to 4-fold extended half-life permitting an 8-week dosing interval and demonstrating non-inferiority in clinical trials with fewer breakthrough hemolysis episodes. However, real-world long-term safety and efficacy data remain limited. The therapeutic landscape for PNH has expanded considerably with the emergence of new anti-C5 monoclonal antibodies such as crovalimab and proximal pathway inhibitors targeting alternative complement activation points including C1, C3, and Factor D. This proliferation of complement inhibitor options has created clinical uncertainty regarding optimal treatment selection and comparative efficacy-safety profiles. The absence of head-to-head randomized controlled trials comparing multiple agents limits evidence-based decision-making for clinicians and patients. 2. Study Aims This systematic review and network meta-analysis aims to comprehensively assess and compare the efficacy and safety profiles of complement pathway inhibitors across all mechanistic classes in the treatment of paroxysmal nocturnal hemoglobinuria in adult patients. Specifically, the analysis will synthesize available randomized controlled trial evidence to evaluate clinically relevant endpoints including hemoglobin change from baseline, transfusion independence, lactate dehydrogenase (LDH) normalization reflecting suppression of intravascular hemolysis, FACIT-fatigue scores assessing quality of life, breakthrough hemolytic events, thromboembolic complications, and serious adverse event profiles. By utilizing network meta-analytic methodology to combine both direct head-to-head evidence and indirect comparative evidence across multiple interventions, this systematic review seeks to establish a comprehensive evidence hierarchy, rank therapeutic options according to efficacy and safety metrics, and provide evidence-based guidance to inform treatment selection in clinical practice and future research priorities. 3. Methods 3.1 Protocol and Registration This systematic review and network meta-analysis will be conducted and reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Extension Statement for Reporting of Systematic Reviews Incorporating Network Meta-Analyses (PRISMA-NMA) 2015 statement and the Cochrane Handbook for Systematic Reviews of Interventions. The study protocol will be prospectively registered on the Open Science Framework prior to commencing data extraction. Statistical synthesis will employ a frequentist framework utilizing the netmeta R package (version 4.5.1) to integrate direct and indirect evidence from randomized controlled trials and generate comparative treatment effect estimates and rankings. 3.2 Eligibility Criteria Eligible studies will include randomized controlled trials of any phase (Phase 1 through Phase 4) and open-label multicenter studies evaluating pharmacologic complement pathway inhibition in adult patients diagnosed with paroxysmal nocturnal hemoglobinuria. Eligible interventions encompass pharmacologic therapies targeting either the terminal complement pathway (including C5 inhibitors such as eculizumab, ravulizumab, crovalimab, and approved biosimilars) or proximal complement pathway components (including C3 inhibitors such as pegcetacoplan, Factor D inhibitors such as danicopan, and Factor B inhibitors such as iptacopan). Eligible comparators will consist of placebo, standard supportive care, or active comparative controls such as eculizumab or ravulizumab. Studies must report at least one primary or secondary clinical outcome, including but not limited to hemoglobin change from baseline, lactate dehydrogenase (LDH) levels, FACIT-fatigue scores, transfusion avoidance or transfusion independence, hemolysis control metrics, or treatment-emergent adverse event frequencies. Studies focusing exclusively on pediatric populations, observational studies including case reports, case series, and cohort studies, systematic reviews, editorials, animal models, in vitro experiments, purely pharmacokinetic modeling studies lacking clinical endpoints, and non-English language publications will be excluded. 3.3 Search Strategy and Study Selection A comprehensive systematic literature search will be conducted across four major electronic databases including PubMed, Embase, Web of Science, and the Cochrane Library, encompassing all records from database inception through December 2025. The search strategy will combine Medical Subject Heading (MeSH) terms and free-text keywords to identify all relevant publications. Using PubMed as the reference example, the search algorithm will be constructed as follows: (paroxysmal nocturnal hemoglobinuria OR PNH) AND (eculizumab OR ravulizumab OR pegcetacoplan OR APL-2 OR danicopan OR ALXN2040 OR iptacopan OR LNP023 OR crovalimab OR ABP 959 OR Elizaria OR Acveris OR complement inhibitor*). No language or publication status restrictions will be imposed during initial screening. Six independent reviewers will perform title and abstract screening, followed by full-text assessment of potentially eligible studies to confirm inclusion criteria. Disagreements regarding study eligibility will be resolved through consensus discussion or referral to a senior investigator. 3.4 Data Extraction and Risk of Bias Assessment Six independent reviewers will conduct standardized data extraction using a piloted and validated extraction form. Extracted data will include study design characteristics such as trial phase, sample size, and duration; patient demographics and baseline clinical features; detailed intervention specifications including drug class, dose, and administration schedule; and all reported clinical outcome measures and safety events. Any discrepancies in extracted data will be adjudicated through discussion or escalation to the principal investigator. Methodological quality and risk of bias for all included studies will be assessed using the Cochrane Risk of Bias tool version 2 (RoB 2), with each methodological domain scored as 1 (low risk), 2 (moderate risk), or 3 (high risk) of bias. Overall confidence in network estimates will be evaluated using the Confidence in Network Meta-Analysis (CINeMA) framework, which provides a transparent and systematic approach to assessing the certainty of evidence in network meta-analyses. 3.5 Statistical Analysis All statistical analyses will be performed using R statistical software version 4.5.1. Network meta-analysis will be conducted using a frequentist random-effects modeling approach implemented via the netmeta package. For dichotomous outcomes including transfusion avoidance or independence and adverse event occurrence, treatment effect estimates will be expressed as risk ratios (RRs) with corresponding 95% confidence intervals (CIs). For continuous outcomes including hemoglobin change from baseline and FACIT-fatigue scores, treatment effects will be quantified using standardized mean differences (SMDs) with 95% CIs. Placebo or standard supportive care will serve as the common reference treatment across all treatment comparisons. Relative ranking of treatments for each outcome will be estimated using P-scores derived from the netrank function, which provide a probabilistic interpretation of treatment hierarchy independent of arbitrary reference treatment selection. 3.6 Assessment of Heterogeneity, Publication Bias, Inconsistency, and Transitivity Statistical heterogeneity across included studies will be quantified using the I² statistic, Tau² estimates of between-study variance, and Cochran's Q test of heterogeneity. Network inconsistency, defined as disagreement between direct and indirect treatment effect estimates, will be evaluated through design-by-treatment interaction models utilizing the decomp.design function to identify global inconsistency and specific comparisons contributing to heterogeneity. Transitivity assumptions, which require that patients enrolled across different comparisons are sufficiently comparable to justify indirect inferences, will be assessed by comparing baseline patient demographics, disease severity, and clinical characteristics across treatment comparisons. To explore and explain identified heterogeneity, univariable meta-regression analyses will be performed examining potential clinical and methodological effect modifiers such as patient gender, baseline hemoglobin, presence of aplastic anemia, trial duration, and study quality metrics. Sensitivity analyses will be conducted excluding one trial at a time to assess the influence of individual studies on network estimates and treatment rankings. Publication bias will be assessed using Egger's test and funnel plot visual inspection for outcomes with sufficient study counts, with statistical significance at p less than 0.05. The certainty of evidence for each network estimate will be comprehensively evaluated using the CINeMA framework, which integrates assessments of within-study bias, indirectness, imprecision, heterogeneity, and publication bias.