Swiss drugmaker Roche Holding has announced that it has dropped out of the project to develop an antibiotic for treating "superbug" infections, Reuters reports.

"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.

NZZ said that Polyphor would now develop the experimental product, which is in phase II clinical trials, alone.

The spokesman added that the company had assessed that "a streamlined development path as originally planned is no longer an option for Roche".

The Roche spokesman also said that Roche would continue to focus on this unmet medical need as part of its infectious disease research and development strategy.

In 2013, Roche had entered into a 500 million Swiss francs ($485.3 million) agreement with Polyphor for rights to the product.

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

Superbug infections, including multi-drug-resistant typhoid, tuberculosis and gonorrhea, kill hundreds of thousands of people a year around the world.