Rapamycin Shows Promise in Preventing Feline Heart Disease FDA Approves New Drug for Early-Stage HCM; New Study Seeks to Confirm Long-Term Benefits
A potential breakthrough in feline medicine is offering new hope to cat owners and veterinarians battling hypertrophic cardiomyopathy (HCM)—a leading cause of sudden death in cats. The drug rapamycin, long studied for its anti-aging properties, is now showing strong potential to prevent or even reverse the progression of HCM in cats.
A Historic Milestone: FDA Approval of Felicyn-CA1
On March 14, the U.S. Food and Drug Administration (FDA) granted conditional approval for felicyn-CA1, a delayed-release formulation of rapamycin (also known as sirolimus), for use in cats with subclinical HCM—a stage before outward symptoms appear. This follows compelling research led by Joshua Stern, DVM, PhD, DACVIM (Cardiology), associate dean at North Carolina State University.
Stern’s study demonstrated that rapamycin can slow or reverse the thickening of the heart muscle—the hallmark of HCM. The result could be life-saving for cats diagnosed early, before symptoms like blood clots, heart failure, or sudden death strike without warning.
“For years, veterinarians could only monitor HCM and hope for the best,” said Stern. “Now, we may finally have a proactive tool to fight back.”
What Is Rapamycin?
Originally discovered in 1972, rapamycin was first noted for its antimicrobial effects. It was later recognized for its immune-modulating and anti-tumor properties, and more recently for influencing the mTOR pathway, which is linked to aging and various chronic diseases. Its use in cats is now being explored for its ability to support cardiac cell health and structure.
The HALT Study: Next Steps in Research
Stern is now leading a larger follow-up trial, HALT (Hypertrophic cardiomyopathy And siroLimus Trial), which aims to enroll hundreds of cats to further assess the drug’s impact. This clinical field study will follow cats for one year, with all medications and testing provided.
Cats must meet criteria such as:
- Elevated proBNP (a heart enzyme)
- Echocardiographic evidence of subclinical HCM
General practitioners can easily test for proBNP and refer eligible patients to participate in HALT.
A Cautious but Hopeful Outlook
Veterinary cardiologist Courtney Smith, DVM, MS, DACVIM, who is involved with the HALT study in Los Angeles, sees promise but urges caution.
“We’re still early in this journey,” Smith said. “There’s no long-term data yet. But if rapamycin holds up under further study, it could change the way we manage HCM.”
While felicyn-CA1 is not a general-use drug and won’t be prescribed for every cat with a heart murmur, its targeted use could significantly reduce the tragic outcomes so often associated with HCM.
Looking Ahead
According to TriviumVet, the Ireland-based manufacturer of felicyn-CA1, the drug could be available to veterinarians by summer 2025. In the meantime, HALT is actively enrolling, and veterinarians can visit the study website to find participation criteria, register patients, and locate study sites.
For cat lovers and clinicians alike, rapamycin may represent the first real hope in the fight against feline HCM—a condition that, until now, left too many questions and too few answers.