By Saumya Joseph and Tamara Mathias

(Reuters) – The U.S. Food and Drug Administration on Tuesday declined to approve Nabriva Therapeutics Plc’s antibiotic for complicated urinary tract infections (cUTI), even as the nation grapples with the growing problem of antibiotic resistance.

The FDA has asked Nabriva to address issues relating to manufacturing deficiencies at one of its contract manufacturers, before the agency can approve the drug, the company said.

The company did not give any further details about why the drug was not given the green light by the U.S. health regulator, but said it would work with the FDA in coming weeks to better understand the decision.

Nabriva’s Contepo, chemically known as fosfomycin, is the first intravenously administered drug from a new class of antibiotics called epoxide in the United States, the company said.

Fosfomycin was first discovered in 1969 and has been used to treat a variety of serious bacterial infections including cUTIs in countries outside the United States.

UTI patients who fail to respond to the initial course of antibiotics often develop a cUTI, wherein the bacteria embed in the bladder wall and multiply, making the condition harder to address with antibiotics.

cUTI often occurs because the right antibiotics were not prescribed, or were not dosed appropriately. At least 20 percent of complications are caused by multidrug resistant bacteria, severely limiting treatment options.

Drugmakers, however, have been shying away from developing antibiotics as combating antimicrobial-resistant pathogens, popularly known as superbugs, has become increasingly challenging.

At least 2 million Americans develop serious infections from antibiotic-resistant bacteria, resulting in nearly 23,000 deaths annually, according to the Centers for Disease Control and Prevention.

The company is also developing another antibiotic, lefamulin, for community-acquired bacterial pneumonia, and the FDA is expected to announce its approval decision by Aug. 19.

Contepo and lefamulin together can treat about 8-9 million people in the United States every year, according to the company.

Nabriva Chief Executive Officer Ted Schroeder said side effects such as nausea and diarrhea that typically occur with the oral formulation of fosfomycin — sold as Monurol by Allergan Plc in the United States and which needs to be administered at higher doses to treat cUTIs — are not common with Contepo.

Wedbush analyst Robert Driscoll estimates peak sales of about $118 million by 2025 for Contepo.

The FDA did not request any new clinical data and did not raise any safety concerns regarding Contepo, Nabriva said.

(Reporting by Saumya Sibi Joseph, Tamara Mathias and Aakash Jagadeesh Babu in Bengaluru; Editing by Sandra Maler)