Rapamune (Sirolimus) is an FDA-Approved immunosuppressant increasingly used in veterinary cardiology to manage hypertrophic cardiomyopathy (HCM) in cats, particularly in early to moderate stages or when standard therapies (atenolol, clopidogrel, etc.) are not sufficient.
Effectiveness
Recent studies (e.g., VET-FAST trial and ongoing research) show that Sirolimus can significantly reduce left ventricular outflow tract obstruction (LVOTO), decrease left atrial size, and improve clinical signs in cats with obstructive HCM. Many cats show reduced heart murmur intensity, improved energy levels, and lower risk of congestive heart failure or arterial thromboembolism within weeks to months of starting therapy.
Administration
Give once or twice daily with or without food. Blood level monitoring (trough levels) is strongly recommended 7-14 days after starting and after any dose adjustment to ensure therapeutic yet safe concentrations.
Dosage
Starting dose is usually 0.3-0.5 mg/kg once every week, targeting trough blood levels of 5-15 μg/mL (varies by laboratory and cardiologist preference). Your veterinary cardiologist will provide exact dosing and monitoring schedule.
Side Effects
- Mild to moderate mouth ulcers/stomatitis (most common)
- Decreased appetite or transient anorexia
- Vomiting or soft stools
- Weight loss, lethargy, or increased liver enzymes Most side effects are dose-dependent and resolve with temporary dose reduction or supportive care (e.g., Mirtazapine, Dental Gel)
IMPORTANCE
The tablet is not allowed splitting or breaking coat to administer
It is highly recommended to be used under direct supervision of a veterinary cardiologist. Regular blood work (CBC, chemistry, trough levels) as well as ultrasound are essential for safe long-term use.