Clinical-stage drug company Cempra Inc. CEMP, -1.15% said Thursday it has received a complete response letter from the U.S. Food and Drug Administration regarding its new drug applications (NDAs) for solithromycin, a treatment for community-acquired bacterial pneumonia. The letter says that the FDA cannot approve the NDAs in their current form and says the company must provide additional safety data and resolve unspecified issues with its manufacturing facility. "Based on their review of the NDAs, the CRL stated that the FDA determined the risk of hepatotoxicity had not been adequately characterized," the company said in a statement. The FDA said the size of the safety database -- 920 patients -- is too small to measure adverse effects, and is recommending a study of about 9,000 patients. The company said it will seek a meeting with the FDA to discuss the issues raised in the letter. "With more than $225 million of cash on hand, patent protection for solithromycin through 2032 and a pipeline that includes fusidic acid and other potential programs for solithromycin, including an ophthalmic formulation, we have flexibility to determine the best course forward for solithromycin and Cempra," Chief Executive David Zaccardelli said in the statement. Shares tumbled 28% premarket and are down 80% for the year through Wednesday, while the S&P 500 SPX, -2.37% has gained about 10%.