Development and Application of an Anaerobic Activity Index

BACKGROUND: Antibiotics with anaerobic activity may result in adverse patient outcomes. Here, we report the development and application of an Anaerobic Activity Index (AAI) to quantify anti-anaerobic antibiotic exposure. METHODS: The numeric AAI was generated for 21 antibiotics using in vitro susceptibility data for seven anaerobic bacterial groups. A binning strategy was applied to susceptibility proportions to result in the fewest antibiotic tied scores. In a cohort of patients with burns, 7-day anaerobic exposure was calculated, multiplied by days of therapy, and summed. Multivariable logistic regression models assessed the association between AAI quartiles and a 90-day composite outcome including culture positivity with bacteria of interest, healthcare-associated infection, and/or death. RESULTS: We included 88 papers reporting on anaerobic activity. The AAI ranged from 4 to 59. Meropenem (59), ertapenem (58), and tigecycline (57) were the highest ranked antibiotics, whereas penicillin (20), doxycycline (13), and aztreonam (4) had the lowest scores. Several antibiotics could not be included for lack of data. In a cohort of patients with burns, the highest seven-day AAI quartile was associated with increased odds of the 90-day composite outcome compared to the lowest quartile (OR: 2.90; 95% CI: 1.65-5.08), adjusting for Baux score and Charlson comorbidity index. CONCLUSIONS: We propose an anaerobic activity index (AAI) assigning numeric scores to commonly used antibiotics. We anticipate that this score will require updating as additional susceptibility data become available. The AAI may be used as a research tool evaluating the impact of anti-anaerobic antibiotics on patient outcomes.