07/09/2025
Sharing this from another group.
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Felycin‑CA1 is an exciting, first-of-its-kind veterinary treatment for cats with subclinical hypertrophic cardiomyopathy (HCM). Here’s what you need to know:
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✅ What is it?
Active ingredient: Sirolimus (also known as rapamycin), formulated in a delayed-release tablet for once‑weekly dosing .
FDA status: Conditionally approved (March 14, 2025) by the FDA’s Center for Veterinary Medicine for managing ventricular hypertrophy in cats with subclinical HCM—the first-ever drug approved for feline HCM .
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🐱 How it’s used
Dose: Target 0.3 mg/kg orally, once weekly .
Tablet strengths: Available in 0.4 mg, 1.2 mg, and 2.4 mg to accommodate different-sized cats .
Availability: Prescription-only, expected to be available in summer 2025 .
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🎯 Mechanism & Research
Mechanism: Sirolimus inhibits the mTOR pathway, reducing ventricular wall thickening in subclinical HCM .
Clinical evidence:
RAPACAT trial (180 days): showed cats on label dose had significantly less increase in wall thickness (average reduction of 0.17 mm) .
Ongoing HALT HCM pivotal trial in ~300 cats across ~25 US sites, to evaluate 12‑month safety and efficacy; slated to complete by 2028 .
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⚠️ Safety & Precautions
Screening needed: Avoid use in cats with pre-existing liver disease or diabetes mellitus .
Monitoring: Liver enzymes (ALT, AST) should be checked 1–2 months after starting, then every 6–12 months. Discontinue if ALT/AST exceed 2× upper limit of normal or signs of liver dysfunction appear .
Drug interactions: Avoid co‑administration with CYP3A4 or P‑gp inhibitors (e.g., some calcium‑channel blockers, azoles, cyclosporine) due to risk of toxicity .
Immunosuppression: At the prescribed dose, unlikely to cause immunosuppression—vaccine response studies suggest it's safe .
Common side effects: Primarily cardiovascular (due to underlying disease progression)—e.g., arrhythmias, CHF, syncope. GI upset (vomiting, diarrhea), lethargy, appetite loss are less common.
First approved HCM treatment
Conditional approval
Convenient dosing
Once-weekly tablets in multiple strengths
Disease-modifying Acts on mTOR pathway to reduce hypertrophy
Safety is manageable
Needs monitoring but low immunosuppression risk
Next steps: Talk to your veterinary cardiologist about screening (liver tests, diabetes), enrolling in ongoing HALT HCM studies, or prescribing Felycin‑CA1 once available. Availability expected by summer 2025 .
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