Cempra tanks on 'positive' Phase III for pneumonia antibiotic

Cempra CEO Prabhavathi Fernandes

Cempra's ($CEMP) in-development treatment for bacterial pneumonia measured up to the now-generic antibiotic moxifloxacin in a Phase III study, but the combination of alarming safety signals and a trial supply issue soured investors on the drug's future.

In a Phase III study involving 863 patients, Cempra's intravenous solithromycin demonstrated noninferiority to injected moxifloxacin, sold as Avelox, in treating community-acquired bacterial pneumonia (CABP) within 72 hours. That was enough to meet the FDA's primary endpoint, Cempra said, but not the two-pronged requirements of the European Medicines Agency.

The EMA wants to see noninferiority both immediately after treatment and after a follow-up 5 to 10 days afterward. And on the latter score, Cempra's drug charted an 86.4% clinical success rate compared to moxifloxacin's 92.8%. Cempra said solithromycin's performance was hampered by a supply shortage that led 5 patients who received its drug to drop out of the study. Taking those volunteers out of the dataset boosts solithromycin's success rate to 87.6%, the company said.

But that doesn't account for the drug's side effect profile. In the trial, 34.3% of solithromycin patients experienced treatment-related adverse events compared with just 13.1% getting moxifloxacin, the company said. The difference was due largely to bad reactions at the site of infusion, according to Cempra.

The results sent Cempra's shares plummeting more than 30% on Friday, negating an earlier spike in value spurred by positive Phase III results for oral solithromycin in January.

The company remains determined to submit the drug for FDA approval in the first half of next year, CEO Prabhavathi Fernandes said.

- read the statement