Phathom Pharmaceuticals Completes Patient Enrollment Ahead of Schedule in Phase 2 pHalcon-EoE-201 Study of VOQUEZNA® (vonoprazan) in Eosinophilic Esophagitis (EoE)

Phathom Completes Enrollment in Phase 2 EoE Trial for VOQUEZNA

Phathom Pharmaceuticals has successfully completed patient enrollment in its Phase 2 pHalcon-EoE-201 clinical trial, evaluating VOQUEZNA (vonoprazan) tablets for eosinophilic esophagitis (EoE) in adults. The study enrolled 95 patients across 41 U.S. sites, achieving this milestone ahead of schedule. Topline results for the 12-week double-blind treatment phase are anticipated in the fourth quarter of 2026. This trial is significant as the first large, placebo-controlled study of an acid suppression treatment in EoE, aiming to assess vonoprazan as a potential new oral, non-steroidal therapeutic option for this chronic condition.

• The pHalcon-EoE-201 study marks a significant step as the first large, placebo-controlled clinical trial to evaluate an acid suppression treatment, vonoprazan, specifically for eosinophilic esophagitis (EoE). This is crucial because while proton pump inhibitors (PPIs) are commonly used off-label for EoE, no acid suppression therapy is currently FDA-approved for this indication. The study aims to determine if vonoprazan can offer a new, oral, non-steroidal option to address this unmet medical need.
• The Phase 2 trial is designed as a two-part, randomized, double-blind, placebo-controlled study. Part 1 successfully enrolled 95 adult patients, all diagnosed with endoscopically confirmed EoE and experiencing dysphagia. These patients were evenly randomized to receive either VOQUEZNA 20 mg or placebo once daily for 12 weeks. The completion of enrollment ahead of schedule across 41 U.S. sites highlights efficient trial execution and progress.
• Phathom Pharmaceuticals expects to report topline results from the 12-week treatment portion of the study in Q4 2026. Positive data from pHalcon-EoE-201 could significantly influence Phathom's future development strategy for vonoprazan in EoE. This includes potential discussions with the FDA regarding further development plans, such as pediatric evaluation, which could lead to an extension of regulatory exclusivity for VOQUEZNA.

Addressing the Unmet Needs in Eosinophilic Esophagitis Treatment

Current treatment approaches for Eosinophilic Esophagitis (EoE) are constrained by a combination of therapeutic gaps, limited comparative evidence, and unresolved questions about long-term disease management. Despite growing mechanistic understanding, translating this into effective, well-tolerated, and durable therapies remains a significant challenge across both adult and pediatric populations.

• Absence of established long-term management strategy: EoE is a chronic inflammatory disease, yet the optimal long-term management approach has not been determined. Recommendations for swallowed topical steroids (STS) are based on relatively few studies employing varied doses and formulations, and there is a notable paucity of direct comparisons among available pharmacologic treatments.

• Limitations of current pharmacologic options: Low-dose budesonide (0.25 mg twice daily) demonstrated a substantial increase in esophageal eosinophil load — from 0.4 to 31.8 eosinophils/high-power field over 50 weeks — though significantly less than placebo. Symptom scores evolved similarly in both budesonide and placebo groups during maintenance therapy, highlighting the disconnect between histologic and symptomatic endpoints.

• Dissociation between cellular targets and clinical outcomes: Eosinophil and mast cell depletion, despite being primary therapeutic targets, does not reliably improve patient-reported symptoms, raising fundamental questions about the mechanistic drivers of symptom burden in EoE.

• Procedural interventions address structural, not inflammatory, disease: Esophageal dilation is used as an adjunct to medical or dietary therapy in fibrostenotic EoE but does not address the underlying inflammatory pathology, limiting its utility as a standalone intervention.

• Immunotherapy-associated risks and impermanence: Desensitization achieved through oral immunotherapy (OIT) tends to be temporary, and EoE is a recognized complication of OIT — with potential similar risk observed with sublingual (SLIT) and epicutaneous (EPIT) immunotherapy approaches. The long-term net effect of OIT on allergic reaction risk remains unresolved.

• Pediatric evidence gap for emerging biologics: Several biologics targeting inflammatory pathways implicated in EoE are under investigation in adults; however, data in pediatric populations remain scarce, limiting the ability to establish evidence-based treatment algorithms for younger patients.

• Suboptimal treatment adherence and delayed diagnosis: Suboptimal adherence was observed in 29.4% of patients in a pediatric cohort. Additionally, symptom overlap with other gastrointestinal disorders continues to delay timely EoE diagnosis, deferring initiation of appropriate therapy.

• Role of dupilumab as a first-line agent remains limited: Although dupilumab is FDA-approved for EoE in patients aged ≥1 year and ≥15 kg, it is unlikely to replace PPIs or STS as first-line therapy except in highly specific clinical circumstances, and its positioning within treatment algorithms continues to be refined.

Unpacking the pHalcon-EoE-201 Study Design for Vonoprazan

The EoE clinical trial landscape spans a broad range of therapeutic modalities—from topical corticosteroids to targeted biologics—each evaluated under distinct but increasingly standardized trial frameworks. Across studies, histologic response thresholds (typically ≤6 eosinophils/high-power field) and validated patient-reported symptom instruments such as the Dysphagia Symptom Questionnaire (DSQ) have emerged as common dual-endpoint anchors, reflecting the field's maturation toward composite efficacy assessments.

Vonoprazan's PCAB Approach in the EoE Treatment Landscape

Several potassium-competitive acid blockers (P-CABs) sharing vonoprazan's mechanism of H⁺,K⁺-ATPase inhibition have been evaluated in clinical trials across acid-related indications, including erosive esophagitis, GERD, and H. pylori eradication. The intervention models employed span parallel-group, crossover, and network meta-analytic designs, reflecting the breadth of comparative evidence being generated in this drug class. Notable agents include tegoprazan, zastaprazan, keverprazan, and the earlier investigational compound AZD0865.

Vonoprazan's Pivotal Test in Eosinophilic Esophagitis

The completion of patient enrollment for Phathom Pharmaceuticals' Phase 2 pHalcon-EoE-201 trial marks a significant moment for the eosinophilic esophagitis (EoE) community. This study, evaluating VOQUEZNA (vonoprazan), is poised to provide crucial insights into the role of potent acid suppression in a disease historically characterized by its complex relationship with gastroesophageal reflux. EoE is a chronic, immune-mediated inflammatory condition causing debilitating symptoms like dysphagia and food impaction, often progressing to esophageal stenosis if left untreated. Current management strategies primarily involve dietary elimination, topical corticosteroids, and endoscopic dilation.

While proton pump inhibitors (PPIs) have been a cornerstone in the diagnostic pathway, helping to identify PPI-responsive esophageal eosinophilia (PPI-REE), their consistent histological efficacy in 'true' EoE has been debated. Vonoprazan, a potassium-competitive acid blocker (P-CAB), represents a mechanistically distinct approach to acid suppression, offering rapid, durable acid control independent of meal timing and genetic variations that affect PPIs. Existing literature suggests vonoprazan's superior efficacy over PPIs in other acid-related disorders and even in some PPI-non-responsive EoE patients in certain populations.

Should the pHalcon-EoE-201 trial yield positive topline results in late 2026, vonoprazan could emerge as a compelling new oral, non-steroidal therapeutic option. This would not only offer a much-needed alternative for patients who fail or cannot tolerate existing therapies but could also redefine the diagnostic and treatment paradigms for EoE. However, several factors warrant careful consideration. The trial must clearly demonstrate efficacy in patients definitively diagnosed with EoE, beyond those with PPI-REE. Furthermore, while the 12-week endpoint will assess initial response, the chronic nature of EoE and the importance of preventing long-term complications like fibrosis mean that future studies would ideally explore sustained efficacy. Finally, given that much of the robust data on vonoprazan's superiority comes from Asian cohorts, its performance in a U.S. adult population will be critical for broader clinical adoption. This trial represents a pivotal step towards potentially expanding the therapeutic arsenal for a challenging and often undertreated condition.