By Priya Raman

Merck KGaA will not move zerlasiran into a late-stage trial, abandoning the investigational heart therapy tied to its planned Silence Therapeutics purchase after a seven-year rival trial failed, Bloomberg reported.

What changed in the cardiac program?

Zerlasiran is designed to lower lipoprotein(a), a cholesterol-carrying particle associated with a higher risk of cardiovascular disease, according to Bloomberg. Merck KGaA shares fell as much as 5% on Thursday, erasing earlier gains that followed the company’s raised full-year outlook, according to Bloomberg.

The company reported third-quarter results and raised its full-year 2026 guidance on Thursday, Bloomberg reported. That combination matters: the company withdrew one deal-linked program on the same day it strengthened its outlook, while the initial market response to the guidance had supported its shares.

Merck KGaA healthcare chief Danny Bar-Zohar called the Novartis data “super disappointing” while speaking with analysts on Thursday, according to Bloomberg. He said: “The drug clearly does pharmacodynamically what it is supposed to do, but clinically, not a lot.”

In plain terms, the treatment changed its intended biological target without delivering a large clinical benefit. Pharmacodynamics describes a drug’s effect on its target; clinical benefit concerns whether that effect improves outcomes.

Why did the Novartis result matter?

Novartis has discontinued development of pelacarsen, its comparable lipoprotein(a)-lowering drug, after a seven-year trial failed to reduce patients’ chances of suffering a heart attack or stroke, Bloomberg reported. The study gave Merck a direct test of the same strategy: lowering lipoprotein(a) had not translated into fewer cardiovascular events.

That distinction sets the mechanism behind Merck’s decision. Bar-Zohar’s assessment pointed to a treatment that produced the intended biological effect without enough clinical benefit, making a late-stage zerlasiran study harder to justify.

What survives in the Silence acquisition?

Merck KGaA still expects the Silence transaction to close in the first quarter of 2027 and said it will add divesiran to its pipeline once the purchase completes, according to Bloomberg. The company described divesiran as a Phase 3-ready siRNA investigational therapy for phlebotomy-dependent polycythemia vera, a rare blood cancer.

SiRNA, or short interfering RNA, is a gene-silencing technology, and Silence Therapeutics is a U.K. biotech specializing in it. Phlebotomy-dependent polycythemia vera means patients require repeated blood removal to manage the condition. Merck KGaA agreed in October to acquire Silence, according to Bloomberg.

The separation preserves a strategic option without retaining the same cardiovascular risk. Divesiran offers a late-stage-ready asset in a rare blood cancer; zerlasiran would have required further clinical development without an encouraging precedent from Novartis’s seven-year study. The disclosed case for the acquisition now rests on a different therapy.

What approvals remain?

Bloomberg reported that the Silence transaction still requires three clear gates before completion:

• Shareholder approval.
• Sanction from the High Court of Justice of England and Wales.
• Regulatory approvals.

Merck KGaA’s first-quarter 2027 closing estimate therefore remained conditional, not settled. The plan now hinges less on developing zerlasiran without an encouraging precedent and more on executing and approving divesiran.

Who is still pursuing the same target?

Other drugmakers continue to work on medicines that target lipoprotein(a), even after Novartis stopped pelacarsen. Amgen is reviewing the detailed Novartis data to understand the implications for the field and its ongoing research, Bloomberg reported. An Eli Lilly spokesperson said that “work is ongoing across the field to understand its potential as a therapeutic target.”

That response does not erase the immediate implication for Merck. It shows that drugmakers still regard the biology as worth testing, while Merck has limited its own exposure by dropping zerlasiran before late-stage development. Merck KGaA is separate from U.S.-based Merck & Co., which is not the company making the Silence transaction.