Effective CSF concentrations achieved with continuous-infusion flucloxacillin in a child

Pharmacodynamics of Flucloxacillin in a Neutropenic Murine Thigh Infection Model: A Piece of the Puzzle towards Evidence-Based Dosing

For decades, flucloxacillin has been used to treat methicillin-susceptible Staphylococcus aureus (MSSA). Little is still known about its pharmacodynamics (PD). The present study aimed to determine the pharmacokinetic (PK)/PD index and the PD-index value minimally required for efficacy. MICs of 305 MSSA isolates were measured to determine the wild-type distribution. The PD of 8 S. aureus, 1 S. pyogenes, and 1 S. agalactiae isolates were evaluated in a neutropenic murine thigh infection model. Two S. aureus isolates were used in a dose-fractionation study and a dose−response analysis was performed additionally in the in vivo model. Data were analyzed with a population PK and sigmoid maximum effect model. The end of the wild-type distribution was 1 mg/L. The percentage of time the unbound concentration was above MIC (%fT > MIC) was best correlated with efficacy. For S. aureus, median %fT > 0.25 × MIC required for 1-log reduction was 15%. The value for S. pyogenes was 10%fT > MIC and for S. agalactiae 22%fT > 0.25xMIC for a 1-log reduction. The effect of flucloxacillin reached a 2-log reduction of S. aureus at 20%fT > 0.25xMIC and also for S. pyogenes and S. agalactiae, a reduction was reached. These data may serve to optimize dosing regimens currently used in humans.

Flucloxacillin does not achieve therapeutic cerebrospinal fluid levels against meticillin-sensitive Staphylococcus aureus in adults: A case report and review of the literature

It is uncertain whether flucloxacillin achieves therapeutic concentrations against meticillin-sensitive Staphylococcus aureus (MSSA) in cerebrospinal fluid (CSF). In this study, plasma and CSF concentrations of flucloxacillin and vancomycin in an adult patient were compared. Unlike vancomycin, the flucloxacillin CSF level was not therapeutic. Flucloxacillin monotherapy should be used with caution for MSSA central nervous system infection in adults.