Alnylam Defends Amvuttra After Wainua’s ATTR-CM Trial Miss

AstraZeneca’s Wainua failed to cut cardiovascular deaths and repeat heart events in 1,432 ATTR-CM patients, most already on a stabilizer. Full results hit the European Society of Cardiology meeting last week, and a Nature Medicine look at the same dataset this week put the stabilizer-background rate ratio at 1.14. Alnylam Pharmaceuticals, which sells the rival silencer Amvuttra, says its HELIOS-B trial was built differently and still supports use with or without a stabilizer.

The split is now a market split. Oral stabilizer makers get to tell cardiologists to start with them. Alnylam keeps the only approved RNA drug for ATTR-CM and has to argue that stacking still pays.

Wainua Added Nothing for Patients Already on a Stabilizer

CARDIO-TTRansform is the largest ATTR-CM outcomes study yet run: 1,432 adults at 130 centres in 20 countries, randomized to eplontersen 45 mg or placebo every four weeks for 140 weeks. AstraZeneca and Ionis Pharmaceuticals said on July 9 that the trial did not meet the primary efficacy endpoint of cardiovascular death plus recurrent cardiovascular events. ESC figures last Friday filled in the miss. There were 381 events in 210 patients on eplontersen and 392 events in 231 patients on placebo (rate ratio 0.89, 95% CI 0.73 to 1.09, p=0.277). Mean age was 72. Women made up 9.4% of the group.

Stabilizer use explains why a drug that did lower circulating transthyretin still lost on events. Some 57% of patients in each arm were already on a stabilizer at baseline, and another 24% in each arm started one during the trial, so about 81% had stabilizer exposure. In patients on a stabilizer at the start, AstraZeneca said no treatment effect was seen. In patients on Wainua alone, fewer composite events were seen, and that result was nominally significant.

The CARDIO-TTRansform trial was designed to examine the role of Wainua, a gene silencer treatment, on top of today’s standard of care in reducing recurring cardiovascular events and mortality. Although the trial did not meet its primary objective, we believe the results support greater scientific understanding of treatment approaches for the hundreds of thousands of patients worldwide suffering from this progressive and often fatal condition.

Sharon Barr, Executive Vice President, BioPharmaceuticals R&D, AstraZeneca

Mathew S. Maurer, MD, who presented the Hot Line in Munich, was blunter about the clinical reading. An estimated 300,000 to 500,000 people live with ATTR-CM worldwide. The protein TTR misfolds and deposits in heart muscle, stiffening the pump and driving heart-failure admissions. Silencing that protein in the blood was supposed to slow the damage even after a stabilizer was on board. In this contemporary cohort, it did not.

Baseline stabiliser use appeared to influence the primary results. No additional benefit was observed in patients receiving background stabiliser therapy, while fewer primary endpoint events were observed with eplontersen in patients not receiving a stabiliser.

Mathew S. Maurer, MD, Columbia University Irving Medical Center, ESC Congress 2026

A rate ratio of 1.14 on a stabilizer is the number now traveling with that conclusion. That Nature Medicine secondary analysis implies more events on the combination, not fewer. Analysts at Stifel had already called a 1.14 figure “clearly worse than expected” when the ESC slides landed. Jefferies analyst Michael Leuchten wrote that the incremental benefit of combining a silencer with a stabilizer may be smaller than HELIOS-B had suggested, rather than CARDIO-TTRansform simply being a poorly designed study. Stifel’s Paul Matteis said he could not see a path to filing in ATTR-CM.

THE TWO OUTCOMES TRIALS

Wainua remains a once-monthly antisense shot already cleared for hereditary ATTR polyneuropathy in more than 20 countries. The heart indication was the expansion that was supposed to make it a large cardiovascular product. That door is now shut unless regulators accept a monotherapy subgroup after a failed primary endpoint, which company commentary has not encouraged.

Alnylam Answers With a HELIOS-B Subgroup

Two days after the Hot Line, Alnylam put a prespecified HELIOS-B cut on the same ESC stage and in the Journal of the American College of Cardiology. Among 655 patients, 40% were on Pfizer’s tafamidis at baseline (259 people). Vutrisiran 25 mg every three months cut the composite of all-cause death and recurrent cardiovascular events through 33 to 36 months, with a hazard ratio of 0.72 (95% CI 0.56 to 0.93, p=0.01), or 28 percent fewer deaths and recurrent heart events than placebo. In the 395-patient group not on tafamidis at the start, the hazard ratio was 0.67 (95% CI 0.49 to 0.93, p=0.02), a 33% reduction. All-cause death through 42 months in the full trial sat at a hazard ratio of 0.65 (95% CI 0.46 to 0.90).

The combination slice is the one Alnylam needs. In patients already on tafamidis, the primary composite showed a rate ratio of 0.79 with baseline tafamidis (95% CI 0.51 to 1.21) versus 0.67 (95% CI 0.49 to 0.93) without it. The interaction p-value was 0.55, so the trial cannot claim a proven difference by stabilizer status, and Alnylam said HELIOS-B was not powered to prove benefit specifically on background tafamidis. All-cause death through 42 months in that tafamidis group had a hazard ratio of 0.59 (95% CI 0.32 to 1.08), a 41% reduction whose confidence interval still crosses 1. About 22% of the vutrisiran monotherapy arm and 21% of the placebo monotherapy arm later started tafamidis, so HELIOS-B was never a pure silencer-versus-nothing study either.

That is a weaker statistical claim than a 1,432-patient miss with an interaction that Nature Medicine treated as real. It is also the only completed silencer outcomes win in ATTR-CM. Amvuttra picked up the cardiomyopathy indication on March 20, 2025, and it is the only TTR silencer approved for both hereditary polyneuropathy and ATTR-CM. The company is now asking physicians to treat HELIOS-B’s directionally consistent subgroup, and its deeper TTR knockdown, as the reason Wainua’s flop should not be read onto vutrisiran or onto nucresiran.

The Antisense Shot Knocked TTR Down Less

Both drugs lower TTR made in the liver. They do not work the same way, and they did not knock the protein down to the same place. A JAMA pooled look at the two trials put mean trough TTR reduction at 81.0% with vutrisiran and 71.9% with eplontersen. John Maraganore, Alnylam’s founding chief executive, used that gap as the company’s simplest public defense the day ESC opened.

And the answer is: eplontersen mean KD 69%, median 76% (cardioTTRansform) vs. vutrisiran mean KD 81%, median 87% (HELIOS-B).

Nucresiran will be even better in TRITON-CM! https://t.co/8f6zvMFpep pic.twitter.com/XMuEnLSyXc

— John Maraganore 🇺🇸🇬🇷🇺🇦 (@JMaraganore) August 28, 2026

“NOT all ‘silencers’ created equal,” he wrote, and pointed to nucresiran’s twice-yearly TRITON-CM study as the next test. The scientific sting in CARDIO-TTRansform is not that TTR failed to fall. Maurer said eplontersen produced the expected suppression through week 140. The sting is that knockdown did not become fewer hospitalizations and fewer cardiovascular deaths once most patients were already on a stabilizer.

HOW THE DRUGS DIFFER

• Stabilizers: Tafamidis (Vyndaqel/Vyndamax) and acoramidis (Attruby) are daily pills that bind TTR’s four-part structure so the protein is less likely to fall apart and form amyloid.
• Antisense silencers: Eplontersen (Wainua) is a monthly shot that tags TTR mRNA for RNase H cutting; patients can self-inject.
• RNAi silencers: Vutrisiran (Amvuttra) is a quarterly shot given by a clinician; it loads into RISC so Argonaute 2 cuts the same mRNA. Nucresiran is meant to do that harder, twice a year.

A pooled analysis of HELIOS-B and CARDIO-TTRansform, covering 2,086 patients, still found a 20% reduction in death and recurrent cardiovascular events for gene silencers as a class (rate ratio 0.80, 95% CI 0.69 to 0.94). That average mixes a win in a less stabilizer-saturated trial with a miss in a more saturated one. Cardiologists reading the interaction are not prescribing a pooled average. They are deciding whether to add a second expensive drug after an oral stabilizer is already in the med list.

First-Line Care Tilts Toward the Oral Stabilizers

BridgeBio’s Attruby, cleared in November 2024, is the stabilizer that has been taking new-to-brand share from Pfizer’s tafamidis, which has been on the ATTR-CM label since 2019. BridgeBio reported $222.4 million in U.S. Attruby net product revenue for the second quarter, inside $243.7 million of total quarterly revenue, with new-to-brand share above 25%. Chief executive Neil Kumar told analysts the Wainua readout did not support stacking.

The case for combination therapy seems today null from a trial data perspective.

Neil Kumar, Chief Executive Officer, BridgeBio, second-quarter 2026 earnings call

That line is doing commercial work. If silencers do not add events benefit on top of a stabilizer, the first prescription in a newly diagnosed patient is an oral drug that costs less than half a silencer’s list price, and the second prescription becomes harder to justify. Pfizer still holds a large installed base on tafamidis. BridgeBio gets to argue that a “near-complete” stabilizer should be the backbone and that knockdown on top of a partial stabilizer was the experiment that just failed. Alnylam keeps monotherapy patients and anyone a clinician already considers a tafamidis progressor. It loses the easy story that every stabilizer patient is a future Amvuttra patient.

Payers are the quiet winners. ATTR-CM therapy was already a six-figure annual bill before anyone stacked classes. A failed add-on trial is a ready reason to demand step therapy: stabilizer first, silencer only after documented progression. Alnylam’s own HELIOS-B design allowed tafamidis and still showed a point estimate in that subgroup that favored vutrisiran. The confidence interval did not. After CARDIO-TTRansform, that interval is what utilization managers will quote.

List Prices Put Combination Therapy Under Payer Pressure

A 2025 state Medicaid review put wholesale acquisition cost at $119,351 per Amvuttra syringe, or $477,404 a year at four doses, against $244,539 for Attruby and $271,710 for tafamidis. Wainua’s listed annual cost was $513,970. Adding Amvuttra’s list price to Attruby’s is $721,943 a year before discounts, rebates, or Medicare’s $2,100 Part D cap on patient out-of-pocket spending for 2026.

ANNUAL LIST PRICES IN THE ATTR-CM STACK

Net prices are lower, and copay cards plus the Medicare cap blunt what patients see. The billed combination is still the number that makes a medical director ask what CARDIO-TTRansform actually bought. Alnylam will answer with HELIOS-B’s 28% composite reduction, quarterly in-clinic dosing, and real-world adherence figures it has cited above 90%. BridgeBio will answer with an oral first-line drug and a trial that showed no extra event benefit when a silencer was layered on. The patient in the middle is often a man in his 70s with wild-type disease who is already on a stabilizer, which is exactly the group that drove Wainua’s miss.

What Nucresiran Still Has to Show

Nucresiran is Alnylam’s next-generation RNAi TTR silencer, given as 300 mg under the skin every six months. In a Phase 1 study, the 300 mg dose cut serum TTR by 90.3% at day 15, 96.5% at day 29, and 92.6% at day 180. TRITON-CM is the ATTR-CM outcomes trial: about 1,750 patients, randomized 2:1 to nucresiran or placebo, stabilizer use allowed, prior TTR-lowering therapy excluded. Alnylam has aimed at an ATTR-CM launch around 2030, with polyneuropathy earlier. The design still tests a silencer on top of whatever oral standard of care exists when those patients enroll.

That is the same structural bet CARDIO-TTRansform made, with a deeper knockdown and a twice-yearly shot. If stabilizer use in TRITON-CM climbs toward the 81% exposure seen in the Wainua study, nucresiran will be asked to show the incremental benefit eplontersen did not. If investigators enroll more silencer-naive, stabilizer-light patients, the trial will look more like HELIOS-B and will not settle the combination question that now sits in front of payers. Either way, the readout is years out. Amvuttra has to carry the silencer side of ATTR-CM until then.

THE ATTR-CM TREATMENT CALENDAR

1. May 2019: Tafamidis wins the first U.S. ATTR-CM label as an oral stabilizer.
2. December 2023: Eplontersen (Wainua) is approved for hereditary ATTR polyneuropathy, not cardiomyopathy.
3. November 2024: Acoramidis (Attruby) is approved as a second oral stabilizer for ATTR-CM.
4. March 20, 2025: Vutrisiran (Amvuttra) is approved for ATTR-CM after HELIOS-B, becoming the only silencer with that label.
5. July 9, 2026: CARDIO-TTRansform misses its primary endpoint on standard of care.
6. August 28, 2026: ESC full data show no added benefit on background stabilizer therapy.
7. August 30, 2026: Alnylam presents the HELIOS-B tafamidis subgroup as evidence that RNAi still adds benefit.

Until TRITON-CM reads out, the practical order of ATTR-CM care is the order CARDIO-TTRansform accidentally wrote down: start with a stabilizer unless a clinician has a reason not to, and treat an add-on silencer as a separate, still-contested decision rather than a default stack.

Frequently Asked Questions

What is ATTR-CM, and who gets it?

ATTR-CM is a buildup of misfolded transthyretin protein in heart muscle, either from an inherited TTR mutation (hereditary) or from aging of the wild-type protein. It is an under-recognized cause of heart failure. Patients often show up with shortness of breath, swelling, palpitations, dizziness, weakness, or fatigue, which is why diagnosis is frequently delayed until imaging or a biopsy is done.

Is Wainua still approved after the heart trial miss?

Yes. Wainua remains approved for the polyneuropathy of hereditary transthyretin-mediated amyloidosis in adults in more than 20 countries, including in the EU under the name Wainzua. AstraZeneca and Ionis have not pointed to a cardiomyopathy filing based on CARDIO-TTRansform, and the drug can still be given as a monthly self-injection for the nerve disease it already treats.

Can Amvuttra be taken with tafamidis or Attruby?

HELIOS-B allowed commercial tafamidis at baseline and later “drop-in,” and safety looked similar for vutrisiran plus tafamidis versus tafamidis alone. The trial was not a randomized head-to-head of combination versus stabilizer monotherapy, and it was not powered to prove the add-on effect. Attruby was not the background stabilizer in HELIOS-B. Any stack is a clinician and payer decision, not a labeled requirement.

Why do TTR silencers come with vitamin A advice?

Transthyretin carries vitamin A in the blood. When a silencer lowers TTR, serum vitamin A falls even if body stores are adequate. Amvuttra’s label advises daily vitamin A at the recommended allowance, warns against extra-high doses meant to “correct” the blood test, and tells patients with night blindness or other eye symptoms to see an ophthalmologist. That counseling is separate from the ATTR-CM outcomes debate.

TRITON-CM will not settle that stack until the end of the decade. Until it does, Amvuttra is the silencer with an ATTR-CM label, Wainua is not, and the first pill most new patients receive is likely to be a stabilizer.

Disclaimer: This article is news reporting and analysis of published trial results and company statements. It is informational only and is not medical advice, a treatment recommendation, or investment advice. Patients with ATTR amyloidosis or heart failure should talk with a cardiologist or amyloidosis specialist before starting, stopping, or combining these medicines, and should not use list prices or trial subgroups as a personal care plan. Figures, approvals, and trial statuses reflect the cited company, congress, and journal sources as of September 2, 2026, and may change as further analyses, labels, or coverage rules are updated.