Felycin-CA1 vs Compounded Rapamycin for Cats: An Honest Comparison

Both are sirolimus — the molecule also called rapamycin. The difference is not the drug, it is the regulatory status, the country you live in, and what your cat has been diagnosed with. We sell one of these, so here is the part usually left out: for a US cat with subclinical HCM, the other one should be your first question.

The short answer

• Cat diagnosed with subclinical HCM, and you are in the US → ask your veterinarian about Felycin-CA1 first. It carries a conditional FDA approval for exactly that, and nothing compounded does.
• Outside the US, or no HCM diagnosis → Felycin-CA1 is generally not available to you, and a veterinarian-directed protocol is the practical route.
• Healthy senior cat, no cardiac diagnosis → you are asking a longevity question, not a cardiac one, and neither product is approved for that.

What Felycin-CA1 is

Felycin-CA1 (TriviumVet, distributed by PRN Pharmacal) is a sirolimus delayed-release tablet for cats. In March 2025 the FDA granted it conditional approval for the management of ventricular hypertrophy in cats with subclinical hypertrophic cardiomyopathy — the first drug ever approved for that condition.

It is dosed at 0.3 mg/kg once weekly and comes in 0.4 mg, 1.2 mg and 2.4 mg tablets.

Two things about "conditional" that matter and are easy to gloss over. It means the manufacturer showed a reasonable expectation of effectiveness rather than the substantial evidence full approval demands, and it must be renewed annually for up to five years while the remaining data is collected. It is a real approval on a genuine evidence pathway — and it is not the same as a fully approved drug.

Where Felycin-CA1 wins

• Regulatory status. A conditional FDA approval for a named feline indication. No compounded preparation has this, ours included.
• A specific, reviewed indication. Subclinical HCM in cats, on the label, assessed by the FDA.
• Manufacturing consistency. A commercially manufactured delayed-release tablet under an approved application, with batch consistency a compounding pharmacy cannot match.
• Cardiology familiarity. US veterinary cardiologists know it and can prescribe it directly.

If your cat is a US cat with subclinical HCM, that list is the answer. Ask your vet about Felycin-CA1.

Where a vet-directed compounded protocol wins

• Availability. Felycin-CA1 is a US product. Across Europe, Türkiye, the Gulf and most of Asia it is not on the shelf, and "the approved option" is not an option.
• Cats without an HCM diagnosis. The Felycin label is subclinical HCM. An owner asking a healthy-ageing question about a nine-year-old cat with a normal echo is outside it.
• Dog households. There is no canine equivalent; dogs are dosed differently (about 0.15 mg/kg weekly) and the TRIAD trial has not reported.
• Included veterinary review. Our price covers the review and the monitoring plan rather than leaving you to arrange them.

Side by side

| | Felycin-CA1 | Vet-directed compounded sirolimus | |---|---|---| | Molecule | Sirolimus | Sirolimus | | Regulatory status | Conditional FDA approval (Mar 2025) | Off-label, prescribed by a licensed vet | | Indication | Subclinical HCM in cats | No approved indication | | Where you can get it | United States | Europe, Türkiye, Gulf, most of Asia | | Dose | 0.3 mg/kg weekly | 0.3 mg/kg weekly (cats) | | Strengths | 0.4 / 1.2 / 2.4 mg | 0.4 / 1.2 / 2.4 mg | | Dogs | Not available | Yes, different dosing |

What neither of them is

Neither is a cure for HCM. Felycin-CA1 is approved to manage ventricular hypertrophy in cats whose disease is subclinical — that is a narrower claim than "treats heart disease", and the distinction is the entire point of the label. And neither product is approved anywhere to extend life in cats. Any seller who tells you otherwise about either one is describing something the evidence does not support.

The same caution applies to both

Sirolimus is not for every cat. Diabetes, active infection, pre-existing liver disease, planned surgery and certain drug interactions all rule it out or require the dose to be paused. This is why the veterinary review is not a formality regardless of which product you end up with.

For the research laid out study by study, with nothing to sell you, see the evidence library at Our Beloved Friends.

If you are outside the US, or your cat is not an HCM case, our feline therapy starts with a veterinary review — and if your cat is not a candidate, you pay nothing. If you are a US owner with an HCM diagnosis, speak to your cardiologist about Felycin-CA1 first; we would rather you had the approved option.