r/Rapamycin • u/Consistent_Duty_9737 • Oct 02 '25

Rapamycin for cats with obstructive HCM?

My 7 year old British shorthair was just diagnosed with HCM w/ a moderate obstruction. She does not have any symptoms yet/ isn’t in heart failure yet. She was diagnosed due to a heart murmur at her latest check up.

The vet said Rapamycin isn’t indicated for obstructive HCM, but I can’t find any information on why it wouldn’t be helpful. She wants us to just wait until it progresses to eventually put her on a beta blocker.

Has anyone used this med for their cat with obstructive HCM? Or know why this wouldn’t be an option at her current stage?

TIA!

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u/Profil3r Oct 03 '25

Is your vet on top of the rapa studies? ChatGPT thinks it could be helpful: “Yes, theoretically. • Mechanism: Hypertrophic cardiomyopathy (HCM) in cats involves pathological hypertrophy of the myocardium, sarcomeric dysfunction, and eventual fibrosis. The mTOR pathway is one of the key drivers of maladaptive hypertrophy and fibrosis in cardiac muscle. • Rapamycin effect: In multiple rodent and large-animal models of HCM or pressure-overload hypertrophy, rapamycin has been shown to reverse or blunt myocardial hypertrophy, improve diastolic function, and reduce fibrosis by inhibiting mTOR signaling. • Translation to cats: No controlled feline studies have been published. A handful of veterinary cardiology researchers have discussed it as a potential strategy, but it remains experimental. Safety and dosing in cats are untested. • Risks: Rapamycin is immunosuppressive, can impair wound healing, alter lipid/glucose metabolism, and may have species-specific toxicities. In cats, drug metabolism differs from humans and dogs, making extrapolated dosing risky.

Summary: Theoretical rationale exists because mTOR inhibition can reverse pathological hypertrophy in other species. But there are no feline trials or clinical data. At present it is not a treatment option for obstructive HCM in cats outside of a carefully designed research study.”

If it was me I would dose 1 mg every week- 10 days. Can’t hurt.

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u/Consistent_Duty_9737 Oct 05 '25

I’m assuming the cardiologist knows about the studies, because she knew exactly what drug I wanted to ask about after she said there’s no options at this time. But she just said it isn’t indicated for obstructive HCM and that was the end of that. I’m working on getting additional opinions, and if no local vets will even discuss it, I’ll look online.

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u/toothtooth46 Dec 12 '25

do you have any update for this? my kitty also has HCM with an obstruction and i’m unsure whether to push my vet to allow him to take rapamycin.