Challener, Doug

Abstract Purpose Data regarding the incidence, onset, and management of complex outpatient antimicrobial therapy–induced neutropenia (COIN) are limited, and pharmacist involvement in COIN management has not been reported. This report describes the incidence, onset, and management of COIN at a large academic medical center. Methods This multisite retrospective cohort study examined adult patients undergoing serum laboratory monitoring for antimicrobials over a 4-year period. Patients receiving chemotherapy or immunosuppressants were excluded. Data collected included the antimicrobial regimen, complete blood count, duration of antimicrobial therapy until outcome occurrence, infectious syndrome, type of intervention, outcome, and pharmacist involvement. Logistic regression was used to assess risk factors for COIN incidence. The primary outcome was the incidence of COIN by antimicrobial drug. Results From 4,261 treatment episodes, 161 cases of COIN were identified (3.8% COIN incidence). The most common antimicrobials associated with COIN were intravenous piperacillin/tazobactam, cefepime, and meropenem. The majority of COIN events were attributed to a combination of at least 2 antimicrobials. Piperacillin/tazobactam was significantly associated with higher odds of developing COIN (odds ratio [OR], 1.86; 95% confidence interval [CI], 1.04-3.34; P = 0.038), whereas ertapenem was associated with significantly lower odds of COIN (OR, 0.43; 95% CI, 0.24-0.77; P = 0.005). The median time to neutropenia diagnosis was 22 days (interquartile range, 14-29 days) from the time of inpatient antimicrobial start. Intervention for COIN occurred in 66.5% of cases, with neutrophil count recovering in 96.9% of these patients. Clinical pharmacists initiated 74.8% of interventions. Conclusion COIN can be effectively identified and managed by a multidisciplinary team reviewing routine laboratory monitoring, enabling most patients to safely complete antimicrobial treatment.