Shares of Tetraphase Pharmaceuticals (TTPH) are down 80% after the company announced that the primary endpoint for its phase 3 IGNITE2 clinical trial of intravenous (transitioning to oral) eravacycline failed to reach statistical significance. The trial  enrolled up to 908 patients who were randomized to  receive therapy of either eravacycline or of the broad-spectrum antibiotic levofloxacin.

More specifically, some patients were given intravenous 1.5 mg/kg eravacycline the first 24 hours followed by oral administration of 200 mg every 12 hours. The other patients were given 750 mg intravenously of levofloxacin the first 24 hours followed by 750 mg orally every 24 hours. The company failed to meet on the primary endpoint of eravacycline being superior to levofloxacin in the trial. 

The IGNITE2 trial was attempting to treat patients with complicated Urinary Tract Infections -- cUTI. Investors were greatly disappointed with these results, thus the big fall in share price. The stock could potentially recover over time, although unlikely to reach previous highs, because the IGNITE1, which used eravacycline for complicated intra-abdominal infections, met  the primary endpoint demonstrating a high cure rate in gram-negative pathogens.