Cefepime versus cefpirome: The importance of creatinine clearance

Standard dosage recommendations for beta-lactam antibiotics can result in very low drug levels in intensive care (IC) patients without renal dysfunction. We compared the pharmacokinetics of two fourth-generation cephalosporins, cefepime and cefpirome, and examined the relationship of drug clearance (CL) to creatinine clearance (CLCR). Two separate but similar pharmacokinetic studies (which used 2 g twice daily for each antibiotic) were conducted. Blood was sampled after an initial and a subsequent antibiotic dose. Drug plasma concentrations were measured, and pharmacokinetic analyses were conducted and compared. The pharmacokinetics of cefepime and cefpirome are similar in IC patients. Any differences in drug CL can largely be attributed to differences in CLCR. Despite normal plasma creatinine concentrations, 54% of patients' antibiotic concentrations were less than the minimum inhibitory concentration (MIC) (4 mg/L) for >20% of the dosing interval. Thirty-four percent of patients had CLCR >144 mL/min (20% higher than the expected maximum of 120 mL/min). Only CLCR was an independent predictor of antibiotic CL. Time above MIC was predicted only by CLCR. Some IC patients have a very large CLCR which results in very low levels of studied antibiotics. Either shortening the dosage interval or using continuous infusions would prevent low levels and keep troughs above the MIC for longer periods. In view of the lack of bedside measurement of cephalosporin levels, we suggest that more frequent use be made of CLCR to allow prediction of small concentrations clinically.

Sub-inhibitory concentrations of ceftazidime and tobramycin reduce the quorum sensing signals of Pseudomonas aeruginosa

Aim: Concentrations of antimicrobials below minimum inhibitory concentration (subMIC) may reduce the production by Pseudomonas aeruginosa of virulence factors such as elastase. We sought to determine whether the reduction in elastase production may be mediated by a reduction in acyl-homoserine lactones. Methods: Pseudomonas aeruginosa in broth was exposed to three conditions for ceftazidime and tobramycin: control, 6% MIC and 25% MIC. Elastase was assayed using elastin congo red. N-(3-Oxododecanoyl)-homoserine lactone (C12-HSL) and N-butyryl-homoserine lactone (C4-HSL) were assayed using biosensor Escherichia coli. Results: Elastase was unchanged with ceftazidime. Elastase was reduced by 16% at 6% MIC tobramycin and reduced by 70% at 25% MIC tobramycin (P

Antibacterial dosing in intensive care: Pharmacokinetics, degree of disease and pharmacodynamics of sepsis

Treatment of sepsis remains a significant challenge with persisting high mortality and morbidity. Early and appropriate antibacterial therapy remains an important intervention for such patients. To optimise antibacterial therapy, the clinician must possess knowledge of the pharmacokinetic and pharmacodynamic properties of commonly used antibacterials and how these parameters may be affected by the constellation of pathophysiological changes occurring during sepsis. Sepsis, and the treatment thereof, increases renal preload and, via capillary permeability, leads to 'third-spacing', both resulting in higher antibacterial clearances. Alternatively, sepsis can induce multiple organ dysfunction, including renal and/or hepatic dysfunction, causing a decrease in antibacterial clearance. Aminoglycosides are concentration-dependent antibacterials and they display an increased volume of distribution (V-d) in sepsis, resulting in decreased peak serum concentrations. Reduced clearance from renal dysfunction would increase the likelihood of toxicity. Individualised dosing using extended interval dosing, which maximises the peak serum drug concentration (C-max)/minimum inhibitory concentration ratio is recommended. beta-Lactams and carbapenems are time-dependent antibacterials. An increase in Vd and renal clearance will require increased dosing or administration by continuous infusion. If renal impairment occurs a corresponding dose reduction may be required. Vancomycin displays predominantly time-dependent pharmacodynamic properties and probably requires higher than conventionally recommended doses because of an increased V-d and clearance during sepsis without organ dysfunction. However, optimal dosing regimens remain unresolved. The poor penetration of vancomycin into solid organs may require alternative therapies when sepsis involves solid organs (e.g. lung). Ciprofloxacin displays largely concentration-dependent kill characteristics, but also exerts some time-dependent effects. The V-d of ciprofloxacin is not altered with fluid shifts or over time, and thus no alterations of standard doses are required unless renal dysfunction occurs. In order to optimise antibacterial regimens in patients with sepsis, the pathophysiological effects of systemic inflammatory response syndrome need consideration, in conjunction with knowledge of the different kill characteristics of the various antibacterial classes. In conclusion, certain antibacterials can have a very high V-d, therefore leading to a low C-max and if a high peak is needed, then this would lead to underdosing. The Vd of certain antibacterials, namely aminoglycosides and vancomycin, changes over time, which means dosing may need to be altered over time. Some patients with serum creatinine values within the normal range can have very high drug clearances, thereby producing low serum drug levels and again leading to underdosing. Copyright © 2010 Elsevier Inc. All rights reserved.