For years, veterinarians have been limited in treating cats with HCM, a serious and often undiagnosed heart condition known as the silent killer. Traditional heart medications for cats targeted the symptoms and severe complications of HCM after they appeared. These traditional treatments showed little advancement in treating HCM to delay the progression of disease or showing a survival benefit in subclinical cats.1,2 Now Felycin-CA1, with the active ingredient sirolimus, gives renewed hope.
The main difference between sirolimus and traditional HCM drugs
Felycin-CA1 (sirolimus delayed-release tablets) is the first and only FDA conditionally approved medication designed to proactively address the underlying disease of early-stage HCM. Unlike older medications, which manage the effects of HCM, Felycin-CA1 is a disease-modifying drug that targets abnormal cellular growth causing the heart wall to thicken. Felycin-CA1 fundamentally shifts the approach to feline HCM management, offering a proactive path forward for cats and the people who care for them.
According to Dr. Ashlie Saffire, DABVP (Feline Practice), founder and lead veterinarian at the Cat Specialty Center at Faithful Friends in Dublin, Ohio: “We have been more reactive with cats experiencing clinical signs of HCM, treating them when the disease was more progressed. Felycin-CA1 gives us a chance to do something for cats earlier in the disease process before they show clinical signs.”
How sirolimus and traditional heart medications compare
The following table highlights the differences between Felycin-CA1 and traditional heart medications.
| Felycin-CA1 (sirolimus delayed-release tablets) | Traditional HCM medications, such as beta blockers, ACE inhibitors, diuretics, anti-clotting medications | |
| Drug Origin | Veterinary-specific formulation developed for cats | Many are medications for people used off-label in cats. Furosemide is a diuretic approved for use in cats with pulmonary edema. |
| Primary Target | The underlying disease (ventricular hypertrophy) | Symptoms and severe consequences (blood clots, fluid buildup) |
| Treatment Approach | Disease-modifying (targets root cause) | Symptom management and decreasing likelihood of complications like blood clots |
| Treatment Goal | Proactive management to slow disease progression | Reactive treatment once symptoms of heart failure appear |
| Target Disease Stage | Subclinical HCM (before symptoms appear) | Clinical-Stage HCM (after symptoms appear) |
| Mechanism of Action | Targets the mTORC1 cellular pathway to modulate cell growth | Systemic effects: manages blood pressure, heart rate, or blood flow |
| Dosing Frequency | Once-a-week oral pill (easy to manage) | Daily or multiple times daily (risk skipping a dose) |
| FDA Status | First and only FDA conditionally approved medication to manage HCM | Many are FDA-approved treatments for people used off-label or for symptom management. The diuretic furosemide is approved for use in cats. |
| Key Clinical Evidence | Backed by the RAPACAT study (specific to feline HCM) | Clinical use based on general veterinary cardiology data, scientific literature on use in animals, and studies supporting the use of furosemide in cats. |
Subclinical HCM: Why early treatment matters
Hypertrophic cardiomyopathy (HCM) is the most common feline heart condition, often remaining subclinical, meaning the cat shows no visible symptoms until the disease has progressed.1 Studies show that 15% of cats have HCM.1,2
How HCM affects cats
HCM causes the heart muscle to thicken, which is known as ventricular hypertrophy. This reduces the heart’s pumping efficiency and can lead to serious complications, including sudden death. Early intervention is critical because once cats begin showing clinical signs (like rapid breathing or lethargy), they may already be in heart failure.
Benefits of treating subclinical HCM
Treating cats with Felycin-CA1 in the subclinical stage of HCM allows your veterinarian to:
- slow or reduce heart muscle thickening before the heart fails as a pump.
- delay or prevent HCM progression to maintain your cat’s quality of life.
Risks of untreated subclinical HCM
If left untreated, HCM in cats can lead to serious complications:
- Congestive heart failure: Fluid builds up in or around the lungs, making breathing difficult.
- Aortic thromboembolism: Causes blood clots, which can travel throughout the body and cause paralysis, most commonly in the hind legs.
- Abnormal heart rhythms: These can sometimes lead to fainting or even sudden death.
Studies show that 23% of cats with HCM suffer cardiovascular mortality within 5 years of diagnosis.1,3
How Felycin-CA1 targets the HCM disease process
Sirolimus is the active ingredient in Felycin-CA1. Unlike traditional heart medications for cats, which manage the symptoms or severe consequences of feline HCM, Felycin-CA1 manages the disease process itself.
It works by targeting a specific cellular pathway—the mTOR pathway—which is involved in cell growth. By modulating this pathway, Felycin-CA1 helps slow or reverse the HCM disease process that’s causing the heart muscle to thicken.
How effective is Felycin-CA1?
Felycin-CA1 has received conditional approval from the FDA, supported by studies that show it is safe and provides a reasonable expectation of effectiveness. The RAPACAT study evaluated the effects of once-weekly Felycin-CA1 on 36 pet cats with subclinical HCM.
- Evidence of efficacy: After 180 days, cats treated with the recommended label dose of Felycin-CA1 had significantly lower thickness of the heart’s left ventricle wall.4 Treated cats showed an average reduction of 17 mm in wall thickness, while placebo cats' thickness increased by 0.94 mm.4
- Important Safety Note: Felycin-CA1 is only for cats with subclinical HCM. It is not recommended for cats already in heart failure or those with pre-existing conditions like diabetes or liver disease.
Frequently Asked Questions
Taking the next step in HCM management
Felycin-CA1 is available now by prescription through veterinarians nationwide. This first-of-its-kind medication for subclinical HCM represents a significant shift from reactive symptom management to proactive disease modification.
If your cat has been diagnosed with subclinical HCM, or if you are concerned about their cardiac health, talk to your veterinarian about whether Felycin-CA1 could help.
References
1 Fuentes VL, Abbott J, Chetboul V, et al. ACVIM consensus statement guidelines for the classification, diagnosis, and management of cardiomyopathies in cats. JVIM 2020;34:1062-1077.
2 Kittleson MD, Cote E. The feline cardiomyopathies: Hypertrophic cardiomyopathy. JFMS 2021;23:1028-1051.
3 Fox PR, Keene BW, Lamb K, et al. International collaborative study to assess cardiovascular risk and evaluate long-term health in cats with preclinical hypertrophic cardiomyopathy and apparently healthy cats: The REVEAL Study. JVIM 2018;32:930-943.
4 Kaplan JL, Rivas VN, Walker AL, et al. Delayed-release rapamycin halts progression of left ventricular hypertrophy in subclinical feline hypertrophic cardiomyopathy: results of the RAPACAT trial. JAVMA 2023;261(11):1628-1637.
