Modithromycin (EDP-420, EP-013420, S-013420) is 6-11-bicyclic erythromycin derivative patented by Enanta Pharmaceuticals, Inc as an antibacterial agent. In preclinical studies, Modithromycin exhibited high levels of in vitro activities against N. gonorrhea, including isolates resistant to azithromycin, cefixime, ceftriaxone, spectinomycin, ampicillin, tetracycline, and ciprofloxacin. Modithromycin also has the good in vivo efficacy against S. pneumoniae and H. influenzae, which might be due to its lasting intracellular activity. In healthy adults, clinical trials Modithromycin shows long half-life and its high systemic exposure. Modithromycin was well tolerated, with no serious or severe adverse events reported, and no subject was discontinued from the study due to an adverse event. In 2005 Modithromycin was studied in phase II clinical trials but no further development reports were published.