No abstract

Inhaled colistin may achieve high drug concentrations in the lung. However, a dose of 80 mg of inhaled CMS every 8 h may not be adequate for the treatment of lower respiratory tract infections due to multi-drug resistant GNB.

Colistin penetration into the cerebrospinal fluid (CSF) was studied in five critically ill adult patients receiving colistin methanesulfonate for infections by multiresistant gram-negative bacilli. Colistin concentrations were determined in paired serum and CSF samples, with the latter taken by lumbar puncture, with the exception of one patient with an external ventriculostomy. CSF-to-serum ratios (0.051 to 0.057) for all study patients coincided at all sampling times. The low level (5%) of penetration suggests inadequate bactericidal colistin concentrations in the CSF.

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Linezolid is a new antimicrobial agent effective against drug-resistant gram-positive pathogens commonly responsible for central nervous system (CNS) infections in neurosurgical patients hospitalized in intensive care units. In order to study the penetration of this antimicrobial into the cerebrospinal fluid (CSF) of such patients, the disposition of linezolid in serum and CSF was studied in 14 neurosurgical patients given linezolid at 600 mg twice daily (1-h intravenous infusion) for the treatment of CNS infections caused by gram-positive pathogens or for prophylactic chemotherapy. Serum and CSF linezolid steady-state concentrations were analyzed by high-pressure liquid chromatography, and the concentration-time profiles obtained were analyzed to estimate pharmacokinetic parameters. The mean ؎ standard deviation (SD) linezolid maximum and minimum measured concentrations were 18.6 ؎ 9.6 g/ml and 5.6 ؎ 5.0 g/ml, respectively, in serum and 10.8 ؎ 5.7 g/ml and 6.1 ؎ 4.2 g/ml, respectively, in CSF. The mean ؎ SD areas under the concentration-time curves (AUCs) were 128.7 ؎ 83.9 g · h/ml for serum and 101.6 ؎ 59.6 g · h/ml for CSF, with a mean penetration ratio for the AUC for CSF to the AUC for serum of 0.66. The mean elimination half-life of linezolid in CSF was longer than that in serum (19.1 ؎ 19.0 h and 6.5 ؎ 3.6 h, respectively). The serum and CSF linezolid concentrations exceeded the pharmacodynamic breakpoint of 4 g/ml for susceptible target pathogens for the entire dosing interval in the majority of patients. These findings suggest that linezolid may achieve adequate concentrations in the CSF of patients requiring antibiotics for the management or prophylaxis of CNS infections caused by gram-positive pathogens.Linezolid is the first member of a new synthetic class of antimicrobials, the oxazolidinones, to be used in clinical practice. It acts by selectively inhibiting the initiation of bacterial protein synthesis with a unique mechanism that precludes cross-resistance to currently available agents (10). In vitro and in vivo studies have demonstrated that linezolid has significant bacteriostatic activity against multiresistant gram-positive pathogens, such as coagulase-negative Staphylococcus species, Staphylococcus aureus, vancomycin-resistant enterococci, and Streptococcus pneumoniae, with MIC 90 s generally ranging from 0.5 to 4 g/ml (5, 26).Gram-positive cocci, mainly staphylococci, are the most frequent pathogens involved in central nervous system (CNS) postneurosurgical infections (26). Severe CNS infections caused by gram-positive pathogens may also be related to head trauma with skull fracture in neurosurgical patients, especially in the presence of an external drainage or ventriculoperitoneal shunt. Thus, these patients require antibiotics either for the management of infections or for prophylaxis against such infections. The frequency of CNS infections subsequent to neurosurgical procedures is estimated to be ϳ4% (25). As the epidemiology of CNS infection in neurosurgical patients evolves and the pr...