However, the following antibiotics have excellent in vitro activity against B fragilis and are effective: Metronidazole Carbapenems (eg, imipenem / cilastatin, meropenem, ertapenem, doripenem) Beta-lactam / beta-lactamase combinations (eg, piperacillin / tazobactam, ampicillin / sulbactam, amoxicillin / clavulanate) Tigecycline Moxifloxacin No single regimen appears to be superior.