Regeneron Ends Phase 2 Heart Failure Trial for REGN5381: What Investors Should Know

Regeneron Pharmaceuticals (REGN) announced an update on their ongoing clinical study.

Regeneron Pharmaceuticals has terminated a mid-stage heart failure trial that was testing REGN5381, an experimental antibody, in adults with heart failure with reduced ejection fraction. Officially titled “A Phase 2, Randomized, Double-Blind, Placebo-Controlled Study to Evaluate the Safety, Pharmacokinetics and Pharmacodynamics of a Single Dose of REGN5381, an NPR1 Monoclonal Antibody Agonist, in Patients With Chronic Heart Failure With Reduced Ejection Fraction,” the study aimed to assess safety and how the drug behaves in the body, as well as early signals of benefit. The update is important because it closes off a potential new heart failure program in Regeneron’s pipeline and may prompt investors to reassess expectations for this specific asset, though not necessarily the company’s broader cardiovascular ambitions.

The study tested REGN5381, a one-time intravenous infusion designed to target specific heart pathways linked to heart failure symptoms and function. Patients received either REGN5381 at different dose levels or a placebo infusion. The goal was to see if a single dose could be given safely, how long it stayed in the bloodstream, and whether patients’ immune systems reacted against it.

This was an interventional Phase 2 trial. Participants were randomly assigned to REGN5381 or placebo, with groups running in parallel rather than in sequence. The study used a “double-blind” approach in which patients, their doctors, the trial staff, and outcome assessors did not know who was getting the active drug or placebo, to limit bias. The main purpose was treatment-focused: to check if REGN5381 could be safely added on top of standard care for chronic heart failure.

The study was first submitted in January 2024, marking its formal start in the public record and signaling early clinical-stage efforts in heart failure for Regeneron. The trial has since been listed as terminated, with the most recent update filed on January 13, 2026, indicating that active dosing and follow-up are no longer ongoing under this protocol. No primary or final completion dates are reported, which suggests the study did not progress to its originally planned endpoints before being stopped.

For investors, the termination removes one potential near- to medium-term driver in Regeneron’s cardiovascular pipeline, which may generate modest disappointment but is unlikely to shift the broader investment case built around its established eye, immunology, and oncology franchises. The update also underscores the high-risk nature of heart failure drug development, an area where large players such as Novartis, AstraZeneca, and others already compete with proven therapies. Market reaction is likely to be muted unless this move is read as part of a wider strategic pullback from cardiovascular R&D; in the absence of such signals, it is more likely to be treated as routine pipeline pruning rather than a thesis-changing event.

The study has been terminated and the latest information is available on the ClinicalTrials.gov portal for investors who want more detail.

To learn more about REGN’s potential, visit the Regeneron Pharmaceuticals drug pipeline page.