Antibiotics firm Cempra reported positive topline data from a U.S. Phase III study evaluating its oral fusidic acid candidate against acute bacterial skin and skin structure infections (ABSSSI). The 716-patient trial met its primary endpoint of noninferiority compared with oral linezolid for early clinical response (ECR). Cempra said it will meet with the FDA to discuss the next steps in the U.S. development and regulatory pathway. 

Sodium fusidate has been used for many years outside the U.S. for the treatment of Gram-positive infections, including both hospital- and community-acquired methicillin-resistant Staphylococcus aureus (MRSA), and as long-term treatment in Europe and Australia for bone and joint infections. The firm initiated a Phase II study in patients with prosthetic joint infections in December 2012.

“We are excited that the results of this Phase III study with fusidic acid confirm the results of our Phase II study and are consistent with the more than 40 years of experience that the product has accumulated outside the United States,” said David Oldach, M.D., Cempra’s CMO. 

The U.S. Phase III fusidic acid trial enrolled 716 patients with ABSSSI infections caused by different organisms, including MRSA, Streptococcus anginosus, Streptococcus pyogenes, and Clostridium spp. The study’s primary endpoint, ECR in the intention-to-treat population, was defined as the proportion of patients whose lesions reduced by at least 20% within 72 hours of starting the study drug, without the use of rescue antibiotics.  A total of 87.2% of patients in the fusidic acid therapy group achieved an ECR, compared with 86.6% of linezolid patients. Trial data also showed that showed that the microbiological response rate was 100% in MRSA-infected patients treated using fusidic acid.

“Considering complicated skin infections are one of the most rapidly growing reasons for hospitalizations and emergency department visits each year, the results with fusidic acid in this study are promising, especially for an outpatient population where there is a need for new oral drugs that are effective against MRSA,” said William O’Riordan, M.D., CMO of eStudySite, which evaluates new therapeutic approaches for complicated skin infections.

In December 2016, Cempra received a complete response letter (CRL) from the FDA refusing to approve two NDAs for oral and intravenous formulations of its lead fluoroketolide antibiotic solithromycin as a treatment for community-acquired bacterial pneumonia (CABP) in adults. The CRL was issued a month after FDA’s Antimicrobial Drugs Advisory Committee narrowly voted (7 to 6) in favor of solithromycin efficacy outweighing its risks for the CABP indication, but voted 12 to 1 that the risk of hepatotoxicity associated with solithromycin had not been adequately characterized.

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