Roche had agreed in 2013 to pay privately held partner Polyphor up to 500 million Swiss francs ($485.3 million) for rights to the product, marking a rare foray by a major pharmaceuticals company into the battle against superbug infections in hospitals.

The deal included milestone payments of up to 465 million francs.

“Roche has decided to discontinue its involvement in the clinical development of the investigational antibiotic RG7929/POL7080 for the treatment of patients with severe Pseudomonas aeruginosa infections and will return the asset to Polyphor,” a company spokesman said by email when asked about a report to this effect by the NZZ am Sonntag newspaper.

The spokesman cited Roche’s assessment that “a streamlined development path as originally planned is no longer an option for Roche.”

Superbug infections, including multi-drug-resistant typhoid, tuberculosis and gonorrhea, kill hundreds of thousands of people a year and the rise of antibiotic resistance has been described by the World Health Organization as “one of the biggest health challenges of the 21st century.”

The Roche spokesman said that antimicrobial resistance remained a major threat to public health and Roche would continues to focus on this unmet medical need as part of its infectious disease research and development strategy.

NZZ said that the experimental product, which is in phase II clinical trials, will now be developed alone by Polyphor. ($1 = 1.0303 Swiss francs)

(Reporting by Michael Shields; Editing by David Goodman)