Peritoneal Dialysis Fluid Concentrations of Linezolid in the Treatment of Vancomycin‐Resistant Enterococcus faecium Peritonitis

OBJECTIVE: To determine linezolid concentrations in peritoneal dialysis fluid after multiple oral doses of the drug in a 46-year-old man with vancomycin-resistant Enterococcus faecium peritonitis who was undergoing peritoneal dialysis. METHODS: After administration of oral linezolid 600 mg twice/day was started, peritoneal dialysis fluid was collected at the end of several 4- and 8-hour dwell times and submitted for analysis of linezolid concentration. Before linezolid therapy was begun, and immediately after several peritoneal dialysis exchanges, 30 ml of expended peritoneal dialysis fluid was collected in a sterile container and immediately frozen at -70 degrees C until analysis by high-performance liquid chromatography. RESULTS: Peritoneal dialysis concentrations of linezolid greater than 4 microg/ml were achieved after the first dose of linezolid and maintained after repeated doses. During the course of therapy, mean linezolid concentrations in peritoneal dialysis fluid tended to increase (mean 7.60 pg/ml, range 3.54-16.2 microg/ml). All assayed peritoneal dialysis samples demonstrated linezolid concentrations greater than 4 microg/ml at the end of 4- or 8-hour dwell times, except for one level after a missed dose on linezolid treatment day 3. Duration of dwell times did not appear to correlate with linezolid concentrations. CONCLUSION: In this patient, linezolid 600 mg twice/day penetrated into peritoneal dialysis fluid at or above the concentrations necessary to treat common gram-positive bacteria. Linezolid therapy is likely to have a role in peritoneal dialysis-associated peritonitis based on its antimicrobial activity, pharmacokinetic properties, ease of administration, and tolerability.