Imbria's Ninerafaxstat Wins FDA Orphan Drug Designation for Non-Obstructive Hypertrophic Cardiomyopathy
Key Insights
Imbria Pharmaceuticals (search) received FDA Orphan Drug Designation for ninerafaxstat, a first-in-class partial fatty acid oxidation inhibitor for symptomatic non-obstructive hypertrophic cardiomyopathy (search) (nHCM).
The designation provides seven years of potential market exclusivity upon approval, tax credits for clinical trials, and PDUFA fee waivers, complementing existing patents extending to 2038 and beyond.
Ninerafaxstat shifts cardiac metabolism from fatty acids to glucose for more efficient energy production, representing a differentiated approach from myosin inhibitors that target contractility.
BOSTON, MA – June 24, 2026 – Imbria Pharmaceuticals (search) announced today that the U.S. Food and Drug Administration has granted Orphan Drug Designation to ninerafaxstat, an investigational oral therapy for symptomatic non-obstructive hypertrophic cardiomyopathy (search) (nHCM). The designation marks a pivotal regulatory milestone for a patient population that currently has no approved pharmacological treatments, and it positions Imbria's first-in-class metabolic modulator as a potential cornerstone therapy in a rapidly evolving cardiovascular landscape.
The Unmet Need in nHCM
Hypertrophic cardiomyopathy, the most common inherited cardiac disease, affects roughly 1 in 500 people. While recent therapeutic breakthroughs have targeted the obstructive form of the disease, approximately one-third of HCM patients have the non-obstructive variant, where thickened heart muscle impairs the heart's ability to relax and fill properly — a state of diastolic dysfunction that compromises cardiac efficiency.
Patients with nHCM endure a substantial symptom burden. Nearly 90% report profound fatigue and shortness of breath, with a majority also experiencing dizziness, chest pain, and palpitations. These symptoms transform everyday activities into significant challenges and are accompanied by risks of atrial fibrillation, stroke, and heart failure. Despite this, current care relies on off-label beta-blockers and calcium channel blockers that manage symptoms without addressing the underlying pathology.
"Despite recent progress in HCM, there are still no approved therapies for nHCM, and patients continue to experience debilitating symptoms, including shortness of breath, fatigue, and exercise intolerance," said Alvin Shih, MD, Chief Executive Officer of Imbria.
A Metabolic Approach to Cardiac Therapy
Ninerafaxstat represents a fundamentally different therapeutic strategy. Rather than altering cardiac contractility, the drug targets mitochondrial energy metabolism. As a partial fatty acid oxidation (pFOX) inhibitor, ninerafaxstat shifts the heart's fuel preference from fatty acids toward glucose, enabling more efficient ATP production. In pathological states like HCM, the heart can become overly reliant on fatty acids — a less efficient fuel source that demands more oxygen to produce the same amount of energy.
This metabolic switch aims to improve cardiac function without affecting blood pressure or heart rate. The approach is grounded in clinical evidence: the Phase 2a IMPROVE-HCM trial, presented at the American College of Cardiology's 2024 scientific session, demonstrated that ninerafaxstat was well-tolerated and produced statistically significant improvements in ventilatory efficiency during exercise — a key predictor of outcomes in HCM — along with reductions in left atrial size, an objective marker of improved diastolic function.
Strategic Value of Orphan Designation
The FDA's Orphan Drug Designation is reserved for therapies targeting conditions affecting fewer than 200,000 people in the United States. For Imbria, the designation confers substantial advantages: seven years of market exclusivity upon approval, tax credits for clinical trial costs, waiver of Prescription Drug User Fee Act (PDUFA) fees, and enhanced access to FDA guidance throughout the development process.
This exclusivity operates independently of Imbria's existing intellectual property portfolio, which includes multiple granted patents extending to 2038 and beyond. "Receiving Orphan Drug Designation for ninerafaxstat is an important milestone as we advance its development for patients living with symptomatic nHCM, a population with significant unmet medical need," said Shih.
The Competitive Landscape
Imbria's progress unfolds amid a shifting therapeutic environment for HCM. Bristol Myers Squibb (search)'s cardiac myosin inhibitor mavacamten (Camzyos), while successful in obstructive HCM, failed to meet its primary endpoints in a Phase 3 nHCM trial, underscoring that the two disease variants may require distinct therapeutic strategies. More recently, Cytokinetics (search) announced positive topline results from a Phase 3 trial of its myosin inhibitor aficamten in nHCM, showing significant improvements in both symptoms and exercise capacity.
Ninerafaxstat's differentiated mechanism — targeting metabolism rather than contractility — positions it as a potentially complementary or alternative option. For patients who cannot tolerate or do not respond to myosin inhibitors, a metabolic modulator could fill a critical gap. The drug's clean safety profile observed thus far, with no adverse effects on cardiac function, further supports its potential as a foundational therapy.
Next Steps
Ninerafaxstat is currently being evaluated in the Phase 2b FORTITUDE-HCM clinical trial (NCT07023614) in patients with symptomatic nHCM. Imbria anticipates reporting topline data in the first half of 2027. "By improving cardiac energetics, ninerafaxstat represents a differentiated approach to addressing nHCM, with the potential to be used as a standalone therapy or in combination with other treatments," Shih noted.
Imbria Pharmaceuticals (search), based in the Boston area, is backed by a syndicate of investors including RA Capital, SV Health Investors, Deep Track Capital, Catalio Capital Management, BNP Paribas, AN Ventures, and Cytokinetics (search).