Big Pharma has been scrambling to restock its pipelines this year-so a disappointing trial from one drugmaker can have an outsize knock-on impact for rivals trying to develop similar treatments.

That dynamic was playing out on Tuesday, as a major setback for Switzerland's Novartis sparked a selloff in Amgen shares.

Amgen stock dropped 5.2% to $414.43 ahead of the opening bell. Futures tracking the Dow Jones Industrial Average slumped 482 points. Amgen is one of the blue-chip index's 30 members.

The selloff came after Novartis said on Friday that its experimental cardiovascular treatment pelacarsen had failed to meet its primary endpoint in a phase three trial.

That doesn't bode well for Amgen's own cardiovascular drug, olpasiran. The company is expected to readout phase three data for that treatment in mid-2028.

"With the Street already pricing in 65%+ probability of success, we're not surprised to see AMGN shares trade down after-hours, particularly with almost two years until data," Cantor analyst Carter Gould wrote in a research note on Friday.

Adding to the misery for the drugmaker was a downgrade. BMO Capital cut Amgen to Market Perform from Outperform with an unchanged price target of $450, according to ratings aggregators.

Still, things could always be worse.

Novartis's Swiss-listed shares plummeted 9.1% on Tuesday after the drugmaker posted disappointing results for another clinical trial, for an experimental neuromuscular treatment. The stock closed 3.1% lower on Monday following the cardiovascular setback.