Novartis shares plunged after the Swiss drugmaker said an experimental neuromuscular medicine missed the primary goal in a late-stage clinical trial, the latest blow to its efforts to find new growth engines.

Shares in Novartis slid 10% shortly after the opening bell Tuesday, wiping out most of the stock's gains since the start of the year. If maintained until close, this would mark Novartis's worst one-day percentage drop since 1987, according to FactSet data.

The latest data mean two out of three pivotal studies for which Novartis released results over the past week fell short of their main targets.

Last week, Novartis said a closely watched cholesterol drug failed to reduce the risk of severe cardiovascular events including deaths, heart attacks and strokes in a trial. However, the company reported positive study results for a multiple-sclerosis pill.

The company also said last week it had paused eight trials of an experimental cell therapy for autoimmune and neurological disorders in late August, after three patients died.

Novartis has been grappling with patent expirations for medicines that used to be among its top-selling products, and turned to dealmaking to revive its pipeline and bolster its growth prospects over the medium term.

The $12 billion acquisition of Avidity Biosciences, which was Novartis's biggest deal in a decade and was completed in February, was a key part of that effort.

The company said Tuesday that the most advanced drug candidate it acquired from Avidity, called del-desiran, didn't meet the primary objective in a late-stage trial for genetic neuromuscular disease myotonic dystrophy type 1.

In the study, del-desiran didn't show a significant improvement compared with placebo on the primary objective, Novartis said. The trial measured how long it took patients with myotonic dystrophy type 1 to open their hand after gripping.

The trial failure means investors' concerns about Novartis's growth beyond 2030 will reemerge, analysts at Jefferies wrote in a note to clients.

Novartis reiterated its guidance for annual sales growth of 5% to 6% over the 2025-30 period.

The company said del-desiran showed evidence of clinical activity for other objectives, and that safety data were generally consistent with previous studies. Novartis said it is evaluating the full dataset and will discuss the most appropriate path forward for the drug with health authorities.

Novartis is advancing two other experimental drugs it added through the Avidity acquisition, it said. Del-desiran and the other two medicines are so-called antibody oligonucleotide conjugates, designed to deliver RNA therapy to muscle cells.