Zilebesiran: The Twice-a-Year RNAi Shot That Silences Angiotensinogen to Lower Blood Pressure - KARDIA-1, KARDIA-2, KARDIA-3 and the Phase 3 ZENITH Outcomes Trial (August 14, 2026)
Table of Contents
- The problem: high blood pressure that daily pills can't keep down
- The target: angiotensinogen, the top of the cascade
- The mechanism: RNA interference with a liver-targeting sugar tag
- KARDIA-1: proof that one shot lowers pressure for months
- KARDIA-2: it works on top of standard blood-pressure drugs
- KARDIA-3: the harder test in higher-risk patients
- ZENITH: the Phase 3 trial that has to prove it prevents events
- Safety and what to watch
- The big picture
The problem: high blood pressure that daily pills can't keep down
Hypertension is the single largest modifiable driver of heart attacks, strokes and cardiovascular death worldwide, and yet a majority of people who take medication for it still never reach their target blood pressure. A big reason is deceptively simple: the drugs work, but they have to be taken every single day, and over months and years adherence slips. Doses get missed, prescriptions lapse, and blood pressure drifts back up. Zilebesiran is built around a radically different idea - what if controlling blood pressure did not depend on remembering a daily pill at all, but on an injection given as infrequently as once or twice a year?
The target: angiotensinogen, the top of the cascade
Blood pressure is governed in large part by the renin-angiotensin-aldosterone system (RAAS), a hormonal cascade that constricts blood vessels and makes the body hold on to salt and water. Every existing RAAS drug - ACE inhibitors, angiotensin receptor blockers (ARBs), and direct renin inhibitors - blocks a step partway down that cascade. Zilebesiran goes to the very top. It targets angiotensinogen (AGT), the single precursor protein, made in the liver, from which the entire system is built: angiotensinogen is cleaved into angiotensin I and then into angiotensin II, the hormone that actually raises blood pressure. Turn down angiotensinogen, and you turn down the whole pathway at its source.
The mechanism: RNA interference with a liver-targeting sugar tag
Zilebesiran (development code ALN-AGT) is a small interfering RNA (siRNA) - a short, chemically stabilized strand of genetic material that uses the body's RNA interference machinery to find and destroy the messenger RNA for angiotensinogen before it can be made into protein. It is conjugated to GalNAc (N-acetylgalactosamine), a sugar tag that binds a receptor found almost exclusively on liver cells, delivering the drug precisely to the hepatocytes where angiotensinogen is produced. This lets a small subcutaneous dose lower circulating angiotensinogen by more than 90% and hold it down for months. Because the suppression is so deep and so durable, a single injection can lower blood pressure for up to half a year - the basis for its every-3-to-6-month (potentially twice-yearly) dosing ambition. It is the same GalNAc-siRNA platform behind lipid drugs such as inclisiran, olpasiran, lepodisiran, zerlasiran and plozasiran, now pointed at blood pressure.
KARDIA-1: proof that one shot lowers pressure for months
The pivotal Phase 2 evidence came from KARDIA-1, published in the New England Journal of Medicine in 2024. The dose-ranging study randomized 377 adults with mild-to-moderate hypertension to single subcutaneous doses of zilebesiran (150, 300 or 600 mg) or placebo, measuring blood pressure with 24-hour ambulatory monitoring. At Month 3, placebo-adjusted reductions in 24-hour mean systolic blood pressure were roughly 14.1 mmHg at 150 mg, 16.7 mmHg at 300 mg and 15.7 mmHg at 600 mg - all highly statistically significant (p<0.0001) - and the effect was durable out to 6 months from that single dose. Serum angiotensinogen fell by more than 90%, confirming the drug was hitting its target hard.
KARDIA-2: it works on top of standard blood-pressure drugs
Real-world patients are usually already on something, so KARDIA-2 tested zilebesiran as an add-on. A single 300 mg dose was layered on top of one of three common background antihypertensives - the diuretic indapamide, the calcium-channel blocker amlodipine, or the ARB olmesartan. Across all three combinations, zilebesiran lowered daytime ambulatory systolic blood pressure by a placebo-adjusted 8.7 to 12.1 mmHg at Month 3, and the reduction was sustained to Month 6. That consistency mattered: it showed the drug adds meaningful control on top of the medications patients are most likely to already be taking.
KARDIA-3: the harder test in higher-risk patients
KARDIA-3, presented as a late-breaker at the European Society of Cardiology Congress in 2025, pushed into a tougher population - patients at higher cardiovascular risk whose blood pressure was still uncontrolled on two to four background medications. Added on to that heavier regimen, zilebesiran produced clinically meaningful office systolic reductions that were maintained through Month 6. The nuance worth being honest about: the single-dose 300 mg office systolic difference at Month 3 - about 5 mmHg versus placebo - did not reach statistical significance on that particular measure, a reminder that added effect gets harder to demonstrate the more background drugs a patient is already on. The fuller ambulatory and durability data, taken together, were enough to carry the program forward and help shape the dose and endpoints for Phase 3.
ZENITH: the Phase 3 trial that has to prove it prevents events
Lower numbers on a blood-pressure cuff are encouraging, but what ultimately matters is whether a drug prevents heart attacks, strokes and cardiovascular deaths. In August 2025, Alnylam and Roche announced they were advancing zilebesiran into ZENITH, a global Phase 3 cardiovascular outcomes trial (CVOT). ZENITH is enrolling roughly 11,000 patients across about 35 countries, testing zilebesiran 300 mg every 6 months against placebo in people with uncontrolled hypertension who already have established cardiovascular disease or are at high cardiovascular risk while on two or more antihypertensives (one a diuretic). Its primary goal is to show a reduction in major adverse cardiovascular events - cardiovascular death, non-fatal heart attack, non-fatal stroke, and heart-failure events. The first patient was dosed in 2025; a positive result would be what turns zilebesiran from a promising blood-pressure lowerer into a proven outcomes drug.
Safety and what to watch
The most distinctive safety consideration flows directly from zilebesiran's greatest strength: its effect is deep and lasts for months, and it cannot be quickly switched off. That makes low blood pressure (hypotension) the key monitored risk - particularly during illness, dehydration, surgery, or when combined with other blood-pressure-lowering drugs - and it means clinicians have to think about RAAS suppression that persists between infrequent doses. As with all RAAS-acting therapies, kidney function and potassium warrant attention, and the drug class is contraindicated in pregnancy because of known fetal risks. Injection-site reactions are the most common side effect seen with GalNAc-siRNA drugs generally. Importantly, zilebesiran is investigational: it is used only under medical supervision in clinical trials, it is not approved, and it is not a supplement or research chemical. Any 'zilebesiran' or 'ALN-AGT' sold by a vendor is unverified and unsafe.
The big picture
Zilebesiran is the first attempt to bring RNA interference - the technology that has already reshaped lipid medicine through drugs like inclisiran, olpasiran, lepodisiran, zerlasiran and plozasiran - into the treatment of high blood pressure. By silencing angiotensinogen at the top of the renin-angiotensin cascade, it offers something no daily pill can: continuous, months-long blood-pressure control from an injection given once or twice a year, aimed squarely at the adherence problem that undermines conventional therapy. Whether that translates into fewer heart attacks and strokes is the question the 11,000-patient ZENITH trial now has to answer. If it does, zilebesiran could mark the start of a new, durable class of cardiovascular medicines that treat chronic risk factors a couple of times a year rather than every morning.
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Citations
- [1] Desai AS, et al. - Zilebesiran, an RNA Interference Therapeutic Agent for Hypertension (KARDIA-1, Phase 2), New England Journal of Medicine (2024) Source
- [2] Roche - Positive topline results from the Phase II KARDIA-2 study in people with hypertension (March 5, 2024) Source
- [3] European Society of Cardiology - KARDIA-3 trial of zilebesiran (ESC Congress 2025) Source
- [4] Roche and Alnylam - Advancing zilebesiran into global Phase III ZENITH cardiovascular outcomes trial (August 30, 2025) Source
- [5] Alnylam Pharmaceuticals - To Advance Zilebesiran into Global Phase 3 Cardiovascular Outcomes Trial Source
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