The antibiotic telithromycin (Ketek, Sanofi-aventis) had two of three treatment indications withdrawn after postmarketing reports of serious and fatal adverse events. The rationale for the withdrawal of specific indications (acute bacterial sinusitis and acute exacerbations of chronic bronchitis), while permitting the drug to remain available for the treatment of community-acquired pneumonia, focused on the lack of demonstrated efficacy from clinical trials that included an active control to which the investigational drug, telethromycin, was determined to be statistically noninferior. This action regarding telithromycin represents a reversal of previous FDA guidelines for the conduct of clinical trials for antibacterial treatment indications and has increased the regulatory risk for future drug development. New clinical trial guidelines have been published that will increase the time and resources required to achieve regulatory marketing approval. This paper reviews recent regulatory actions and discusses the impact these new guidelines will have on future antibacterial clinical trial designs and challenges.