Novartis: its experimental treatment del-desiran fails in phase III

Novartis announced on Tuesday, 8 September 2026, the failure to meet the primary endpoint in the phase III HARBOR study evaluating delpacibart etedesiran, better known as del-desiran, in patients with type 1 myotonic dystrophy. The experimental treatment did not show a statistically significant improvement over placebo on the primary measure of hand relaxation.

Type 1 myotonic dystrophy is a progressive neuromuscular disease that causes muscle weakness and difficulty relaxing muscles after contraction. Novartis emphasizes that no approved treatment currently exists to directly address this disease.

The randomized, double-blind HARBOR study involved approximately 150 patients followed for 54 weeks. The company reports observing signals of clinical activity on certain secondary and exploratory endpoints, while the safety profile remained generally consistent with previously known data.

The Swiss group must now analyze all results and consult with health authorities to determine the next steps for del-desiran’s development. No timeline has been announced for a potential new study or program modification.

The setback is closely watched by investors because del-desiran was part of the assets acquired in the purchase of Avidity Biosciences. Novartis completed this deal for approximately 12 billion dollars to strengthen its portfolio of experimental treatments for neuromuscular diseases.

A second clinical setback in a few days

The announcement comes just days after another advanced Novartis program, pelacarsen, failed to meet its primary endpoint in a phase III cardiovascular study. This string of negative results increases scrutiny on the group’s ability to renew its portfolio ahead of patent expirations on several key drugs.

On the Swiss stock exchange, Novartis shares dropped sharply Tuesday following the announcement. However, the company maintained its target for average annual sales growth of 5% to 6% over the period 2025-2030.

The group is simultaneously continuing development of other therapies from Avidity’s platform, notably for certain forms of muscular dystrophy. In such programs, full trial results and regulatory discussions typically determine whether a treatment is discontinued, modified, or evaluated in a new study. Clinical development stakes also concern other hard-to-treat diseases: for example, Rwanda recently launched the world’s first clinical trial for a treatment against the Marburg virus..