Etripamil AFib-RVR Phase 3 Launch: Promising Phase 2 Signal, Uncharted Regulatory Path, Unresolved Safety Overhang

Milestone Initiates Pivotal Phase 3 for Etripamil in AFib-RVR

Milestone Pharmaceuticals has initiated the pivotal Phase 3 ReVeRA-301 trial for etripamil nasal spray, evaluating it as a self-administered treatment for atrial fibrillation with rapid ventricular rate (AFib-RVR). The trial uses the same 70 mg repeat-dose regimen as the FDA-approved CARDAMYST for paroxysmal supraventricular tachycardia (PSVT). This study aims to address the significant unmet need for an effective self-administered option for AFib-RVR patients, potentially reducing their reliance on emergency department visits. Previous Phase 2 data showed etripamil reduced ventricular rate and improved symptoms in AFib-RVR.

• Trial Design and Patient Population: The ReVeRA-301 trial is a multinational, multi-center, randomized, double-blind, placebo-controlled Phase 3 study. It aims to enroll approximately 150 patients with AFib-RVR, who will self-administer the 70 mg dose of etripamil nasal spray in an unsupervised setting. This design mirrors the regimen approved for PSVT, building on the drug's established safety profile and potential for at-home use.
• Key Endpoints and Regulatory Strategy: The primary endpoint for ReVeRA-301 is the reduction in ventricular rate (VR) within 30 minutes of administration. A crucial secondary endpoint focuses on symptom improvement, measured via patient-reported outcomes, reflecting the patient-centric goal of the therapy. Milestone Pharmaceuticals is pursuing a single-study supplemental new drug application (sNDA) registration pathway for etripamil in AFib-RVR, leveraging existing data and the drug's FDA approval for PSVT.
• Addressing Significant Unmet Need: AFib-RVR represents a substantial burden, affecting over 6 million patients in the U.S., with 30-40% experiencing episodes requiring urgent medical care, often involving emergency department visits. Current acute management options are limited. The development of a self-administered treatment like etripamil could significantly improve patient quality of life and reduce healthcare system strain, building on promising Phase 2 data that demonstrated reduced VR and improved symptom relief.

The Urgent Need for Self-Administered AFib-RVR Treatment

Current treatment approaches for AFib-RVR face a constellation of clinical and evidentiary gaps that complicate both acute management and longer-term decision-making. From unclear agent preference to persistent thromboembolic risk despite screening, these limitations collectively underscore the inadequacy of existing protocols for a broad patient population.

• Lack of clarity on first-line agent selection: No patient-specific factors have been identified to guide preferential use of β-blockers versus nondihydropyridine calcium channel blockers in acute AFib-RVR management, leaving clinicians without evidence-based criteria for individualized treatment decisions.

• Modest rate control efficacy: First-line agents demonstrate limited effectiveness, with rate control achieved in only 35% of patients receiving metoprolol and 41% receiving diltiazem — underscoring that a substantial proportion of patients fail to respond adequately to initial therapy.

• Adverse event burden, particularly with diltiazem: Total adverse event incidence reached 19% with diltiazem versus 10% with metoprolol, with higher baseline heart rates correlating with greater adverse event rates — yet robust comparative safety data remain scarce.

• Conflicting guidance for heart failure patients: Diltiazem is generally contraindicated in heart failure due to negative inotropic effects, yet some evidence suggests comparable safety outcomes with metoprolol in this population, creating clinical uncertainty. Compounding this, heart failure patients are frequently excluded from comparative trials altogether.

• Persistence of thromboembolic events despite screening: Thromboembolic events following direct-current cardioversion have been documented in patients with no detectable left atrial thrombus or appendage sludge on transesophageal echocardiography, indicating that current pre-cardioversion screening methods do not reliably identify all at-risk individuals.

• Structural limitations in the evidence base: Available data are constrained by small sample sizes, heterogeneity in dosing protocols, and underrepresentation of key patient subgroups — collectively impeding the development of definitive, broadly applicable treatment guidelines.

Unpacking the ReVeRA-301 Pivotal Trial for AFib-RVR

The AFib-RVR evidence base draws predominantly from retrospective, single-center studies conducted in emergency department settings, with sample sizes ranging from 45 to 359 patients. Study designs span retrospective chart reviews, cohort studies, and at least one prospective observational study, reflecting the practical and logistical constraints of studying an acute, time-sensitive condition. Enrollment periods generally ranged from one to four years, with several studies specifically isolating heart failure with reduced ejection fraction (HFrEF) subpopulations to assess rate control safety in a higher-risk cohort.

Etripamil's Established PSVT Role and Expanding AFib-RVR Potential

Beyond its investigational use in AFib-RVR, etripamil has an established and well-characterized clinical trial programme in paroxysmal supraventricular tachycardia (PSVT), specifically atrioventricular nodal-dependent PSVT. Multiple Phase 3 trials have evaluated its self-administered intranasal formulation across both supervised and unsupervised real-world settings, with varying dose regimens and control designs.

• NODE-301 Trial (NCT03464019): A Phase 3, multicentre, double-blind, placebo-controlled study using a 2:1 randomization to etripamil 70 mg or placebo, employing a single-dose regimen administered intranasally at symptom onset.

• RAPID Trial (NCT03464019): A randomized, double-blind, placebo-controlled multicentre trial conducted across 160 sites in North America and Europe, using 1:1 randomization to etripamil 70 mg or placebo, with a repeat-dose regimen allowing an optional second dose 10 minutes after the initial administration.

• NODE-302 Trial (NCT03635996): An open-label extension study with a single-arm design, enabling patients to self-treat multiple discrete PSVT episodes over time, providing longitudinal safety and efficacy data beyond index-episode evaluation.

• NODE-303 Trial (NCT04072835): An open-label, single-arm study assessing at-home self-administration for multiple PSVT episodes without a supervised test dose prior to first use, utilizing a single- or repeat-dose regimen (70 mg with an optional repeat dose at 10 minutes).

• Across all four trials, the common intervention model was patient-initiated intranasal self-administration in medically unsupervised settings, a design feature that distinguishes etripamil's development programme and directly informs its patient-centric therapeutic positioning.

Pivoting Etripamil to Transform AFib-RVR Care

The initiation of the pivotal Phase 3 ReVeRA-301 trial for etripamil nasal spray represents a significant strategic move, aiming to extend the utility of this rapid-acting L-type calcium channel blocker beyond its established role in paroxysmal supraventricular tachycardia (PSVT) to the broader and often more complex landscape of atrial fibrillation with rapid ventricular rate (AFib-RVR). This trial leverages the same 70 mg repeat-dose regimen that proved effective in PSVT studies like RAPID, where etripamil demonstrated superior and rapid conversion to sinus rhythm, empowering patients to self-manage episodes outside of a clinical setting.

For AFib-RVR, the need for a self-administered, acute treatment is substantial. Patients frequently experience symptomatic episodes that necessitate emergency department visits for intravenous rate control, placing a considerable burden on both individuals and the healthcare system. Early evidence from the Phase 2 ReVeRA-201 study for AFib-RVR is encouraging, showing significant reductions in ventricular rate and improvements in patient-reported symptoms. Furthermore, a post-hoc analysis from the NODE-303 study, which included patients whose presumed PSVT episodes were later identified as AF, also indicated clinically significant and sustained ventricular rate reduction.

However, the path forward is not without considerations. The efficacy and safety data for AFib-RVR thus far come from relatively smaller cohorts, underscoring the critical need for the ReVeRA-301 trial to robustly confirm these findings in a larger, more diverse AF population. While generally well-tolerated, the occurrence of transient severe bradycardia and syncope in one ReVeRA-201 patient, attributed to hyper-vagotonia, highlights the importance of vigilant safety monitoring in a broader patient group. Moreover, the experience from the initial PSVT Phase 3 (NODE-301), which did not meet its primary 5-hour endpoint despite showing earlier treatment effects, emphasizes the necessity of precise endpoint definition and adequate statistical power in ReVeRA-301. If successful, etripamil could redefine acute AFib-RVR management, offering patients an unprecedented level of control over their condition and potentially alleviating a major strain on acute care resources.