Novartis Shares Slide as Avidity’s Del-Desiran Fails Phase III HARBOR

Novartis Shares Slide After $12B Avidity Drug Fails Its Pivotal Trial

Del-desiran, the lead muscle-disease therapy Novartis bought with Avidity for $12 billion, missed its main goal in myotonic dystrophy — sending the stock to its worst day since 2020.

By iPharmag Editorial Desk · Sep 9, 2026 · 1 min read

Conceptual illustration of an antibody-RNA conjugate near muscle fibers with a downward trend

Conceptual illustration. Novartis’ Avidity-acquired del-desiran missed its Phase III goal in myotonic dystrophy.

Novartis shares tumbled after del-desiran (delpacibart etedesiran), the lead asset it gained by acquiring Avidity Biosciences for $12 billion in February 2026, failed its Phase III trial.

The HARBOR trial, in myotonic dystrophy type 1 (DM1) — an inherited disease that progressively weakens muscles — missed its primary endpoint: a statistically significant improvement over placebo in video Hand Opening Time (a measure of the muscle-relaxation problem central to DM1) through week 54.

Why the drug was interesting

Del-desiran is an antibody-oligonucleotide conjugate (AOC) — a muscle-targeting antibody (aimed at transferrin receptor 1) linked to a small interfering RNA designed to degrade the toxic DMPK messenger RNA that drives DM1. The AOC approach was the crown jewel of the Avidity deal, so the miss cuts deep.

Why it matters

Investors reacted sharply: Novartis fell ~11% in Zurich and ~14% on the NYSE — its worst single-day drop since March 2020. “Developing therapies for a complex disease like DM1 remains challenging, and setbacks are part of scientific progress,” said CMO Shreeram Aradhye. Novartis says it will review the full HARBOR dataset and talk to regulators about a path forward. For a company that paid a premium for a platform, the result is a reminder that even elegant biology has to clear the clinic. Business/clinical news, not investment advice.

Frequently asked questions

What is del-desiran?

Delpacibart etedesiran (del-desiran) is an antibody-oligonucleotide conjugate: a muscle-targeting antibody linked to a small interfering RNA designed to degrade the toxic DMPK messenger RNA that drives myotonic dystrophy type 1. It was the lead asset from Novartis’ $12B Avidity acquisition.

What happens next?

Novartis says it will evaluate the full HARBOR dataset and engage regulators to determine the appropriate development path forward. The Phase III miss does not by itself end the program, but it is a major setback.

This article is for general information only and is not medical advice. Consult a qualified healthcare professional for any medical decisions.