Antibiotic‐associated neutropenia is marked by the depletion of intestinal Lachnospiraceae and associated metabolites in pediatric patients

Prolonged antibiotic exposure causes dangerous hematologic side effects, including neutropenia, in up to 34% of patients. Murine studies established a link between the intestinal microbiota and hematopoiesis. To identify factors that predispose to neutropenia in pediatric patients, we evaluated changes in microbiota-derived metabolites and intestinal microbiota composition after prolonged courses of antibiotics. In this multi-center study, patients with infections requiring anticipated antibiotic treatment of two or more weeks were enrolled. Stool samples were obtained at the start and completion of antibiotics or at neutropenia onset (prospective arm). Some patients were enrolled in a retrospective arm in which a stool sample was collected at the time of neutropenia during antibiotic therapy and 2-4 weeks after completion of antibiotics with recovery of blood counts. We identified 10 patients who developed neutropenia on antibiotics and 29 controls matched for age, sex, race, and ethnicity. Clinical data demonstrated no association between neutropenia and the type of infection or antibiotic used; however, patients with neutropenia were admitted to the intensive care unit more often and received longer courses of antibiotics. Reduced intestinal microbiome richness and, specifically, decreased abundance of