Nov 19 (Reuters) - Germany's Bayer has aborted a large late-stage trial testing a new anti-clotting drug due to lack of efficacy, dealing a fresh blow to the embattled drugmaker and throwing its most promising medium-term development project in doubt.

It said in a statement late on Sunday that experimental anticoagulant asundexian, which it had hoped would generate annual sales of more than 5 billion euros ($5.5 billion), was shown to be inferior to Bristol-Myers Squibb and Pfizer's established Eliquis in preventing strokes in high-risk patients part-way into a Phase III trial.

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 by U.S. lawsuits over the alleged carcinogenic effect of its commonly used Roundup weedkiller.

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 management decision-making, cutting management positions.

Bayer said it will further analyse the data of the discontinued trial, known as OCEANIC-AF, which was initiated in August 2022. The trial's safety data was consistent with previous studies, it added.

It said the independent trial supervisors recommended the continuation of a separate phase III trial, OCEANIC-STROKE, testing asundexian to prevent repeated strokes in participants who have already suffered one.

Both OCEANIC studies combined would have involved up to 30,000 patients, Bayer said last year in August.

Bayer in January laid out a goal for asundexian to generate more than 5 billion euros in peak annual sales, seeking to 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 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 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. ($1 = 0.9168 euros) (Reporting by Ludwig Burger in Frankfurt and Jose Joseph in Bengaluru; Editing by Miranda Murray and Christopher Cushing)