AstraZeneca Hit by Partner's Late-Stage Heart Drug Trial Failure

What happened

On July 9, AstraZeneca and partner Ionis Pharmaceuticals announced that Wainua (eplontersen) failed to meet its primary goal in a Phase 3 trial for ATTR-CM, a progressive heart disease where misfolded proteins damage the heart muscle. The 140-week study tested whether adding Wainua to standard care could reduce cardiovascular deaths and recurring heart events in patients. It did not. The drug is already approved and selling in over 20 countries for a separate nerve condition, but this trial was meant to open a second, fast-growing market. Ionis shares dropped sharply following the news, falling from around $86 to $64 in a single session.

Why the stock moved

AstraZeneca's stock likely slipped following the Wainua trial failure because the company co-developed the drug with Ionis and stood to share in potential revenue from the ATTR-CM indication. The miss removes a commercial opportunity in a market analysts viewed as significant. The immediate 24% drop in Ionis shares reflected investor disappointment over the lost expansion path. A day later, Roche ended two separate Huntington's disease programs with Ionis, compounding concerns about the partner's pipeline strength. That added an 8% decline, pushing Ionis down nearly 29% over five sessions, which may have weighed on sentiment around AstraZeneca's collaboration as well.

Bigger picture

The trial failure shifts the competitive landscape in ATTR-CM treatment. Rivals including Alnylam Pharmaceuticals, BridgeBio, and Pfizer already market approved therapies for the condition, and Wainua's setback leaves them with less near-term competition. BofA Securities noted the surprise outcome may reflect a changing treatment environment, as more patients now begin stabilizer drugs earlier in their disease course. Despite the disappointment, most analysts maintained Buy ratings on Ionis while cutting price targets, suggesting the damage is seen as specific to this indication rather than a broader pipeline problem. Ionis reported first-quarter revenue of $246 million and guided 2026 revenue to a range of $875 million to $900 million, indicating the company's commercial base remains intact.

What investors watch

Full trial data will be presented at the European Society of Cardiology Congress in August. Investors will look for any patient subgroups that showed benefit, as one prespecified analysis on Wainua alone did show a small but meaningful risk reduction. That presentation could clarify whether a narrower approval path remains viable. AstraZeneca and Ionis also have two other regulatory decisions on separate drugs expected before year-end, which will test the strength of their broader collaboration. Analyst price target cuts ranged from Jefferies' $113 to $90 down to Needham's $105 to $86, but most firms kept positive ratings, signaling cautious optimism pending upcoming catalysts.