Pharmacokinetics of linezolid during continuous hemodiafiltration: A case report

Correlation of antimicrobial fraction unbound and sieving coefficient in critically ill patients on continuous renal replacement therapy: a systematic review

Background

Fraction unbound has been used as a surrogate for antimicrobial sieving coefficient (SC) to predict extracorporeal clearance in critically ill patients on continuous renal replacement therapy (CRRT), but this is based largely on expert opinion.

Objectives

To examine relationships between package insert-derived fraction unbound (Fu-P), study-specific fraction unbound (Fu-S), and SC in critically ill patients receiving CRRT.

Methods

English-language studies containing patient-specific in vivo pharmacokinetic parameters for antimicrobials in critically ill patients requiring CRRT were included. The primary outcome included correlations between Fu-S, Fu-P, and SC. Secondary outcomes included correlations across protein binding quartiles, serum albumin, and predicted in-hospital mortality, and identification of predictors for SC through multivariable analysis.

Results

Eighty-nine studies including 32 antimicrobials were included for analysis. SC was moderately correlated to Fu-S (R2 = 0.55, P < 0.001) and Fu-P (R2 = 0.41, P < 0.001). SC was best correlated to Fu-S in first (<69%) and fourth (>92%) quartiles of fraction unbound and above median albumin concentrations of 24.5 g/L (R2 = 0.71, P = 0.07). Conversely, correlation was weaker in patients with mortality estimates greater than the median of 55% (R2 = 0.06, P = 0.84). SC and Fu-P were also best correlated in the first quartile of antimicrobial fraction unbound (R2 = 0.66, P < 0.001). Increasing Fu-P, flow rate, membrane surface area, and serum albumin, and decreasing physiologic charge significantly predicted increasing SC.

Conclusions

Fu-S and Fu-P were both reasonably correlated to SC. Caution should be taken when using Fu-S to calculate extracorporeal clearance in antimicrobials with 69%–92% fraction unbound or with >55% estimated in-hospital patient mortality. Fu-P may serve as a rudimentary surrogate for SC when Fu-S is unavailable.

Dosage regimen and toxicity risk assessment of linezolid in sepsis patients

BACKGROUND

Significant alterations in the pharmacokinetic characteristics of linezolid are often seen in sepsis patients. The study aimed to identify a target pharmacokinetics/pharmacodynamics (PK/PD) index of the efficacy of linezolid treatment, and to estimate the optimum dosage regimen of linezolid in sepsis patients.

METHODS

The PK data were modeled using the one-compartment model, which determined the target PK/PD index for successful treatment by logistic regression. The probability of thrombocytopenia was identified by establishing a logistic model. Different dosing regimens were evaluated using Monte Carlo simulation.

RESULTS

Reaching 80% bacterial eradication required an AUC₂₄/MIC of 100, which defined the therapeutic target. The proposed regimen to attain a cumulative fraction of response ≥80% was 800 mg/12 h (safety probability 66.8%) for sepsis patients with normal renal function or mild kidney damage. By contrast, the target cumulative fraction of response was attained with a standard dosing regimen in sepsis patients on continuous renal replacement therapy [600 mg/12 h (safety probability 49.7%)].

CONCLUSIONS

This study identified different dosing strategies to achieve target linezolid PK/PD values according to whether sepsis patients were treated with continuous renal replacement therapy. Due to the high incidence of thrombocytopenia in sepsis patients on continuous renal replacement therapy, therapeutic drug monitoring should be encouraged for optimizing linezolid exposure in sepsis patients.