Early Use of Realgar-Indigo Naturalis Formula (RIF) Combined With All-trans Retinoic Acid (ATRA) for Treating Acute Promyelocytic Leukemia (APL).

Background and Rationale Acute promyelocytic leukemia (APL) is a distinct subtype of acute myeloid leukemia (AML) characterized by the t(15;17) translocation, resulting in the PML-RARα fusion gene. The introduction of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) has transformed APL into a highly curable disease. However, early death (ED), defined as mortality within 30 days of diagnosis, remains a significant challenge, particularly in high-risk patients (initial white blood cell \[WBC\] count \>10×10⁹/L). The predominant cause of ED is hemorrhagic complications, often intracranial hemorrhage, driven by a severe coagulopathy resembling disseminated intravascular coagulation (DIC). Real-world data indicate an ED rate of approximately 12% overall, increasing to 17.6% in the high-risk subset. Thus, interventions that can rapidly stabilize coagulopathy and mitigate bleeding risk during the initial days of therapy are critical to improving overall outcomes. Realgar-Indigo Naturalis Formula (RIF) is an oral arsenic-containing Chinese patent medicine. Preclinical and clinical studies suggest that RIF has a pharmacodynamic profile distinct from intravenous ATO, potentially offering a more rapid correction of coagulation parameters. Prior pivotal trials have established its non-inferiority to intravenous ATO for consolidation therapy in low-to-intermediate risk APL, with the added advantages of oral administration and a favorable safety profile suitable for outpatient management. Furthermore, a small randomized study reported zero early deaths among patients receiving ATRA plus RIF during induction, with observations suggesting faster recovery of platelet counts and fibrinogen levels compared to ATO in patients with subclinical DIC. These findings provide the rationale for evaluating whether the early introduction of RIF during the critical pre-diagnosis and initial induction period can reduce the incidence of early fatal events. Study Design and Rationale This is a multicenter, randomized, open-label, controlled trial designed to evaluate the impact of early RIF administration on early death in patients with newly diagnosed AML highly suspected to be APL. The open-label design is necessitated by the distinct nature of the interventions (oral RIF vs. no RIF), and the primary endpoint (early death) is an objective, hard endpoint not subject to assessment bias. The study employs a pragmatic, response-adaptive treatment framework. Patients are randomized prior to molecular confirmation of APL to reflect a real-world clinical scenario where prompt initiation of targeted therapy is critical. The initial 7-day window (Days 0-7) is the focus of the intervention, aiming to test the hypothesis that early RIF combined with ATRA yields superior early mortality outcomes compared to ATRA alone. Upon confirmation of PML-RARα positivity, patients in the experimental group transition to a standard ATRA + ATO regimen, while control patients initiate ATRA + ATO from Day 0. This design ensures that all confirmed APL patients ultimately receive guideline-directed therapy with ATRA and ATO, isolating the variable of early RIF exposure. Patients who are found to be PML-RARα-negative are withdrawn from the study and managed according to standard clinical practice for non-APL AML. Treatment Regimen and Supportive Care Details The induction phase is protocolized with specific supportive care measures to manage APL-related complications. Coagulopathy Management: Aggressive supportive care is mandated, with platelet transfusions to maintain counts ≥30-50×10⁹/L and cryoprecipitate or fibrinogen concentrate to maintain fibrinogen levels \>1500 mg/L. The protocol emphasizes that these supportive measures are to be initiated immediately upon clinical suspicion of APL, prior to randomization, to minimize confounding from supportive care variability. Management of Hyperleukocytosis: For patients with WBC \>10×10⁹/L, hydroxyurea (0.1 g/kg) is initiated. If WBC continues to rise despite hydroxyurea, the protocol allows for the addition of venetoclax, with dosing adjusted based on WBC counts and under close safety monitoring. Mannitol infusion is also specified for this high-risk subgroup to reduce the risk of intracranial complications. Differentiation Syndrome (DS) Management: A standardized approach to DS is defined. Mild DS (2-3 criteria) and severe DS (≥4 criteria) are managed with a tiered approach involving temporary interruption of ATRA/arsenic and administration of dexamethasone (10 mg IV every 12 hours) for a minimum of 3 days until symptom resolution. Consolidation and Maintenance Therapy Following achievement of molecular complete remission (MCR),in the consolidation phase, intermediate- and low-risk patients receive either intravenous ATO or oral RIF, while high-risk patients receive intravenous ATO together with intravenous mannitol infusion. Routine lumbar puncture and intrathecal chemotherapy are not performed.No anthracyclines are used during either induction or consolidation phases, minimizing long-term cardiotoxicity and standardizing treatment across study arms. This design ensures that any differences in long-term outcomes, such as 2-year event-free survival (EFS) and overall survival (OS), can be attributed to the early induction strategy rather than variations in post-remission therapy. Safety Monitoring and Pharmacovigilance Given the use of arsenic-containing compounds, a rigorous safety monitoring plan is implemented. Cardiac Monitoring: Electrocardiograms (ECGs) are performed at baseline and weekly during induction to monitor the QTc interval. Any QTc prolongation \>480 ms, after correction of electrolyte imbalances, triggers a predefined management algorithm including dose adjustment or temporary suspension of arsenic therapy. Arsenic Toxicity Monitoring: Regular assessments of hepatic and renal function are conducted. The protocol includes specific criteria for dose modifications or treatment interruption in the event of grade 3 or 4 hepatotoxicity or nephrotoxicity. Adverse Event Reporting: All adverse events (AEs) are graded according to the Common Terminology Criteria for Adverse Events (CTCAE). Serious adverse events (SAEs) are reported to the sponsor and the ethics committee within 24 hours. A pre-specified interim safety analysis is planned if the incidence of differentiation syndrome exceeds 20% or if any unexpected safety signals emerge. Statistical Considerations and Data Management The sample size calculation is predicated on a reduction in the primary endpoint of early death from a historical rate of 12% to 3% in the experimental group. To account for potential attrition due to PML-RARα negativity, a total of 224 patients (112 per arm) will be enrolled, providing 80% power at a two-sided alpha of 0.05. The primary analysis will be conducted on the intention-to-treat (ITT) population, defined as all randomized patients with a confirmed diagnosis of APL. A per-protocol analysis will also be performed to assess the effect of treatment adherence. Kaplan-Meier methodology will be used to estimate 2-year EFS and OS, with comparisons between groups performed using the log-rank test. A Cox proportional hazards model will be employed to explore the impact of baseline risk factors (e.g., WBC count, fibrinogen level) on survival outcomes. All clinical data will be captured using an electronic data capture (EDC) system compliant with ICH-GCP and CDISC standards. Data quality is ensured through automated range checks, logical validation, and source data verification at participating sites. Anonymized data will be stored securely at the sponsor institution (Xi'an Jiaotong University First Affiliated Hospital) and will be accessible only to authorized personnel for analysis and regulatory review.