No Clinical Benefit With Double Anaerobic Therapy for Intra-Abdominal Infections

Combination therapy with piperacillin/tazobactam plus metronidazole was associated with worse clinical outcomes than piperacillin/tazobactam in surgically managed patients with intra-abdominal infections (IAIs), according to research presented at IDWeek, held virtually from October 21 to 25.

Against guideline recommendations, piperacillin/tazobactam is often used in combination with metronidazole for IAIs, resulting in unnecessary double anaerobic therapy. In this retrospective, single-center study, researchers evaluated length of hospital stay, in-hospital postoperative complications, and readmission within 30 days of discharge due to postoperative complications in adult patients who received piperacillin/tazobactam plus metronidazole vs piperacillin/tazobactam between January 1, 2016 and June 30, 2019.

Of 163 patients, 67 patients (mean age, 53.1 years) received double anaerobic therapy, and 96 patients (mean age, 46.3 years) received single anaerobic therapy. Compared with patients who received single anaerobic therapy, patients who received double anaerobic therapy had higher rates on the Charlson Comorbidity Index (P =.021), 5-day postoperative body temperature (P =.013), and higher risk for surgical site infections (P =.002). Patients treated with double anaerobic therapy had more gastrointestinal perforations (40.2% vs 12.5%; P <.0001) and acute cholecystitis (9.1% vs 36.1%; P =.0001) compared to those treated with single anaerobic therapy.

Although readmissions within 30 days of discharge due to postoperative complications was higher in patients who received single anaerobic therapy (3.9% vs 1.4%; P <.0001), patients who received double anaerobic therapy had longer mean length of hospital stay (10 vs 6 days; P <.0001), and more in-hospital postoperative complications (23% vs 8.8%; P <.0001).

Aggregate resampling conducted to adjust for physicians prescribing double anaerobic therapy more often in patients with severe disease for a longer period of time yielded similar results.

The results of this study cannot be generalized to immunocompromised patients, since only a small number of patients were immunocompromised.

Study results show that “double anaerobic coverage is associated with worse clinical outcomes.” Study authors emphasize that the “approach of single anaerobic coverage supports avoiding excessive use of metronidazole without compromising clinical outcomes.”


Raymond L, Cani E, Zeana C, Lois W, Park TE. Clinical outcomes of single versus double anaerobic coverage for intra-abdominal infections. Presented at: IDWeek 2020; October 21-25, 2020. Poster 719.