Its shares slid 16.4% at 0903 GMT on Monday to their lowest in 12 years, with separate news overnight the company had been ordered to pay $1.56 billion in the latest U.S. lawsuit over its commonly-used Roundup weedkiller also hitting sentiment.
Bayer said in a statement late on Sunday that experimental anticoagulant asundexian was shown to be inferior to Bristol-Myers Squibb (BMY.N) and Pfizer's (PFE.N) established Eliquis in preventing strokes in high-risk patients part-way into a Phase III trial.
It had hoped the drug would generate annual sales of more than 5 billion euros ($5.5 billion) and replace revenue from one of its pharmaceutical best-sellers, blood thinner Xarelto, which is set to lose protection from key European patents in 2026.
The trial halt, which followed recommendation of independent trial supervisors, marks another setback for a company burdened by a weak herbicide business, high debt and U.S. lawsuits over Roundup.
New Bayer CEO Bill Anderson is weighing options to break apart the maker of prescription drugs, consumer health products, crop chemicals and seeds, in a bid to revive a battered share price. He is also seeking to simplify decision-making, cutting management positions.
Markus Manns, a portfolio manager at Union Investment in Germany, said Anderson now faced "Herculean" challenges.
"Removing asundexian from our model suggests significant challenges ahead for the company's pharma business," Barclays analysts said, adding this was a total surprise.
BLOW TO US EXPANSION HOPES
Bayer said it would further analyse the data of the discontinued trial, known as OCEANIC-AF, which was initiated in August 2022 with a targeted 18,000 participants. The trial's safety data was consistent with previous studies, it added.
It said the independent trial supervisors recommended the continuation of a separate smaller phase III trial, OCEANIC-STROKE, testing asundexian to prevent strokes in participants who have already suffered one.
Both OCEANIC studies combined would have involved up to 30,000 patients, Bayer has said.
The trial halt is also a blow for the head of Bayer's pharmaceutical unit Stefan Oelrich, who had pinned hopes of a major expansion in the United States - by far the world's largest pharmaceutical market - on asundexian.
In contrast to the Xarelto franchise, where Bayer shared development costs with Johnson & Johnson (JNJ.N) and ceded most of the U.S. market to its partner, Bayer opted to go it alone on asundexian studies and was ready to spend heavily on U.S. marketing and distribution.
Union Investment's Manns said the development costs should have been shared.
"How asundexian was handled is another example of failed risk management at Bayer," he said, adding that Bayer was now lacking sustainable growth prospects.
The compound belongs to a novel drug group known as factor XI inhibitors, which has attracted Novartis (NOVN.S), working with private equity firm Blackstone, and Bristol-Myers Squibb (BMY.N), working with J&J.
Asundexian is one of four new drug hopefuls that Bayer in January said had combined peak sales potential of more than 12 billion euros.
($1 = 0.9168 euros)
