Clarifying the Role of Adjunctive Metronidazole in the Treatment of Biliary Infections

TO THE EDITOR—Infectious diseases specialists face a challenging era highlighted by multidrug-resistant pathogens and antimicrobial resistance. These issues have fueled increasing emphasis on antimicrobial stewardship [1, 2]. Essential in antimicrobial stewardship is the practice of appropriate antibiotic use and avoidance of unnecessary antimicrobial agents. One such example is the often unnecessary double anaerobic coverage therapy [3]. In the setting of complicated intra-abdominal infections, data suggests that implementation of stewardship programs effectively reduces unnecessary antimicrobial use [4]. The Infectious Diseases Society of America (IDSA) guidelines for diagnosis and management of complicated intraabdominal infections [5] thoroughly outline the appropriate use of antimicrobials for various diagnoses. However, some confusion arises upon further review. In Table 4 of the guidelines addressing initial empiric treatment of biliary infection in adults, except for mild-to-moderate, community-acquired cholecystitis, the recommendations for antimicrobial therapy are stated as “imipenem-cilastatin, meropenem, doripenem, piperacillin-tazobactam, ciprofloxacin, levlofloxacin or cefepime, each in combination with metronidazole.” The wording suggests the invariable addition of metronidazole to every antibiotic listed, even antibiotics with significant anaerobic activity such as carbapenems and extended spectrum penicillin-beta lactamase inhibitors. Recommendation 61 in the text adds further ambiguity by stating that “anaerobic therapy is not