Cempra Inc said on Thursday the U.S. Food and Drug Administration had rejected its antibiotic for community-acquired bacterial pneumonia (CABP), citing inadequate data on the drug's impact on the liver and manufacturing issues.
The company's stock tumbled 48.3 percent to $3.15 in premarket trading.
The FDA did not ask for further data on solithromycin's effectiveness in treating CABP, Cempra said.
An independent FDA panel narrowly backed the drug, solithromycin, in November, although a preliminary staff review by FDA scientists highlighted a potentially concerning rise in liver enzymes associated with its use.
The elevations were transient in Cempra's trials and data showed no cases of acute liver injury.
Solithromycin, designed to be administered intravenously and via capsules, is descended from Ketek, a controversial drug made by Sanofi SA that was approved by the FDA in 2004.
It was later linked to dozens of serious or fatal liver problems, and eventually discontinued.
Solithromycin is a next-generation version of a class of oft-prescribed antibiotics called macrolides, which are used to fight pathogens that cause CAPB.
The FDA's rejection letter noted that the available 920-patient dataset on solithromycin was too small to fully understand the potential risk of liver injury.
The agency recommended an additional 9,000-patient study to rule out the risk, Cempra said.
Even if there is no such event in the new study, the drug's label will include a warning of the potential for liver toxicity and the drug's use will be limited to patients with few options.
Given the size and cost of the proposed new study, and likely restrictive labeling, Cempra will probably not continue to develop solithromycin, Morgan Stanley analyst Andrew Berens said in a client note.
Cempra revealed in October that there were quality control issues with its main manufacturer, India's Wockhardt Ltd.
The FDA also cited deficiencies in recent inspections of manufacturing plants owned by Wockhardt and Pfizer Inc's Hospira unit, and said the issues must be resolved before solithromycin can be approved.
Cempra, whose chief executive and founder Prabhavathi Fernandes retired earlier this month, has found another manufacturer in India-based Vivimed Labs Ltd's Spanish business, Uquifia.
About half of the most common bacteria, the pneumococcus that cause chest and other infections, are resistant to macrolides, making the quest for new antibiotics pressing.
Unrestrained overuse of current antibiotics, often when they are not needed, and widespread use in livestock, have contributed to the evolution of antibiotic-resistant bacteria.
(Reporting by Natalie Grover and Akankshita Mukhopadhyay in Bengaluru; Editing by Shounak Dasgupta and Ted Kerr)