Time-kill curves as a tool for targeting ceftazidime serum concentration during continuous infusion

A sensitive and high-throughput quantitative liquid chromatography high-resolution mass spectrometry method for therapeutic drug monitoring of 10 β-lactam antibiotics, linezolid and two β-lactamase inhibitors in human plasma

An ultra-high pressure liquid chromatography high-resolution mass spectrometric (UHPLC-HRMS) method was developed for the simultaneous and sensitive quantification of 10 β-lactam antibiotics (cefepime, meropenem, amoxicillin, cefazolin, benzylpenicillin, ceftazidime, piperacillin, flucloxacillin, cefuroxime and aztreonam), linezolid and β-lactamase inhibitors tazobactam and clavulanic acid in human plasma. Validation according to the EMA guidelines showed excellent within- and between-run accuracy and precision (i.e. between 1.1 and 8.5%) and high sensitivity (i.e. lower limit of quantification between 0.25 and 1 mg/L). The UHPLC-HRMS method enables a short turnaround time and high sensitivity and needs only a small amount of plasma, allowing appropriate routine therapeutic drug monitoring. The short turnaround time is obtained by speeding up the protocol on multiple levels, i.e. fast and workload-efficient sample preparation (i.e. protein precipitation and dilution), short (4 min) instrument run time, simultaneous measurement of all relevant β-lactam antibiotics used in the intensive care unit and the use of the same instrument, column and mobile phases as for the other routine methods in our laboratory.

Prolonged Versus Intermittent Infusion of β-Lactam Antibiotics: A Systematic Review and Meta-Regression of Bacterial Killing in Preclinical Infection Models

BACKGROUND

Administering β-lactam antibiotics via prolonged infusions for critically ill patients is mainly based on preclinical evidence. Preclinical data on this topic have not been systematically reviewed before.

OBJECTIVES

The aim of this study was to describe the pharmacokinetic/pharmacodynamic (PK/PD) indices and targets reported in preclinical models and to compare the bactericidal efficacy of intermittent and prolonged infusions of β-lactam antibiotics.

METHODS

The MEDLINE and EMBASE databases were searched. To compare the bactericidal action of β-lactam antibiotics across different modes of infusion, the reported PK/PD outcomes, expressed as the percentage of time (T) that free (f) β-lactam antibiotic concentrations remain above the minimal inhibitory concentration (MIC) (%fT_>MIC) or trough concentration (C_min)/MIC of individual studies, were recomputed relative to the area under the curve of free drug to MIC ratio (fAUC₂₄/MIC). A linear mixed-effects meta-regression was performed to evaluate the impact of the β-lactam class, initial inoculum, Gram stain, in vivo or in vitro experiment and mode of infusion on the reduction of bacterial cells (in colony-forming units/mL).

RESULTS

Overall, 33 articles were included for review, 11 of which were eligible for meta-regression. For maximal bactericidal activity, intermittent experiments reported a PK/PD target of 40-70% fT_>MIC, while continuous experiments reported a steady-state concentration to MIC ratio of 4-8. The adjusted effect of a prolonged as opposed to intermittent infusion on bacterial killing was small (coefficient 0.66, 95% confidence interval - 0.78 to 2.11).

CONCLUSIONS

Intermittent and prolonged infusions of β-lactam antibiotics require different PK/PD targets to obtain the same level of bacterial cell kill. The additional effect of a prolonged infusion for enhancing bacterial killing could not be demonstrated.

Therapeutic drug monitoring of β-lactam antibiotics in the ICU

INTRODUCTION

Individualizing antibiotic therapy is paramount to improve clinical outcomes while minimizing the risk of toxicity and antimicrobial therapy. β-lactam antibiotics are amongst the drugs most commonly prescribed in the Intensive Care Unit (ICU). The pharmacokinetics of β-lactam antibiotics are profoundly altered in critically ill patients, leading to the failure of standard drug dosing regimens to result in adequate drug concentrations. Therapeutic Drug Monitoring (TDM) of β-lactam antibiotics is a promising tool to help optimize β-lactam antibiotic therapy.

AREAS COVERED

The rationale behind TDM for β-lactam antibiotics is explained, as well as some more practical aspects such as when to sample, what concentrations to strive for and how to use it in clinical practice. We also discuss microbiological and analytical considerations, knowledge gaps, and future perspectives of β-lactam antibiotics TDM in ICU patients.

EXPERT OPINION

TDM of β-lactam antibiotics has been studied intensively in recent years. While TDM may not yet be widely available, and targets need to be further refined, TDM of β-lactam antibiotics will help to optimize antibiotic therapy in the critically ill patient, as an integrated part of an antimicrobial stewardship program.

Optimizing β-lactams treatment in critically-ill patients using pharmacokinetics/pharmacodynamics targets: are first conventional doses effective?

INTRODUCTION

The pharmacokinetic/pharmacodynamic index determining β-lactam activity is the percentage of the dosing interval (%T) during which their free serum concentration remains above a critical threshold over the minimum inhibitory concentration (MIC). Regrettably, neither the value of %T nor that of the threshold are clearly defined for critically-ill patients. Areas covered: We review and assess the targets proposed for β-lactams in critical illness by screening the literature since 1997. Depending on the study intention (clinical cure vs. suppression of resistance), targets proposed range from 20%T > 1xMIC to 100%T > 5xMIC. Assessment and comparative analysis of their respective clinical efficacy suggest that a value of 100%T > 4xMIC may be needed. Simulation studies, however, show that this target will not be reached at first dose for the majority of critically-ill patients if using the most commonly recommended doses. Expert commentary: Considering that critically-ill patients are highly vulnerable and likely to experience antibiotic underexposure, and because effective initial treatment is a key determinant of clinical outcome, we support the use of a target of 100%T > 4xMIC, which could not only maximize efficacy but also minimize emergence of resistance. Clinical and microbiological studies are needed to test for the feasibility and effectiveness of reaching such a demanding target.

Antimicrobial treatment of febrile neutropenia: pharmacokinetic-pharmacodynamic considerations

Patients with cancer or hematologic diseases are particularly at risk of infection leading to high morbidity, mortality and costs. Extensive data show that optimization of the administration of antimicrobials according to their pharmacokinetic and pharmacodynamic parameters improves clinical outcome. Evidence is growing that when pharmacokinetic and pharmacodynamic parameters are used to target not only clinical cure but also eradication, the selection resistance is also contained. This is of particular importance in patients with neutropenia in whom increasing rates of drug-resistant Gram-negative bacteria have been reported, particularly Pseudomonas aeruginosa. Based on experimental and clinical studies, pharmacokinetic and pharmacodynamic parameters are discussed in this review for each antibiotic used in febrile neutropenia in order to help physicians improve dosing and optimization of antimicrobial agents.

Continuous versus intermittent infusion of cefepime in neurosurgical patients with post-operative intracranial infections

Cefepime is administered as an intermittent infusion (II); however, continuous infusion (CI) may be advantageous because β-lactam antibiotics exhibit time-dependent antibacterial activity. This retrospective, non-randomised, comparative study included 68 neurosurgical patients with post-operative intracranial infections treated with 4g/day cefepime over 24h as a CI (n=34) or 2g every 12h as II (n=34). CI controlled the intracranial infection more rapidly and effectively than II (6.6±1.9 days vs. 7.8±2.6 days; P=0.036). By considering the minimum inhibitory concentrations (MICs) to be 4μg/mL and 8μg/mL, the percentage of time when the cefepime plasma or CSF concentrations were higher than the MIC (%T>MIC) was calculated for each patient. For plasma cefepime concentrations, the %T(>MIC) in the CI group was higher than in the II group (for MICs of 8μg/mL, 100% vs. 75%, respectively). The mean calculated area under the curve (AUC) in the CI group was similar to the II group (1197.99±72.15μgh/mL vs. 890.84±140.78μgh/mL; P=0.655). For CSF cefepime concentrations, the %T(>MIC) in the CI group was higher than in the II group (for MICs of 4μg/mL and 8μg/mL, 83.3% and 75% vs. 25% and 0%, respectively). The mean calculated AUC for the CI group was higher than the II group (220.56±13.59μgh/mL vs. 86.34±5.69μgh/mL; P=0.003). Therefore, CI of cefepime significantly enhanced the antibacterial effect and reduced the treatment duration in neurosurgical patients with post-operative intracranial infections.

High-dose continuous infusion beta-lactam antibiotics for the treatment of resistant Pseudomonas aeruginosa infections in immunocompromised patients

OBJECTIVE

To report a case series of high-dose continuous infusion beta-lactam antibiotics for the treatment of resistant Pseudomonas aeruginosa infections.

CASE SUMMARY

Continuous infusion ceftazidime or aztreonam was administered to achieve target drug concentrations at or above the minimum inhibitory concentration, when possible, in 3 patients with P. aeruginosa infections. The maximal calculated target drug concentration was 100 mg/L. In the first patient, with primary immunodeficiency, neutropenia, and aggressive cutaneous T-cell lymphoma/leukemia, continuous infusion ceftazidime (6.5-9.6 g/day) was used to successfully treat multidrug-resistant P. aeruginosa bacteremia. In the second patient, with leukocyte adhesion deficiency type 1, continuous infusion aztreonam (8.4 g/day) was used to successfully treat multidrug-resistant P. aeruginosa wound infections. In the third patient, with severe aplastic anemia, continuous infusion ceftazidime (7-16.8 g/day) was used to treat P. aeruginosa pneumonia and bacteremia. In each patient, bacteremia cleared, infected wounds healed, and pneumonia improved in response to continuous infusion ceftazidime or aztreonam.

DISCUSSION

Treatment strategies for multidrug-resistant P. aeruginosa infections are limited. A novel treatment strategy, when no other options are available, is the continuous infusion of existing beta-lactam antibiotics to maximize their pharmacodynamic activity. High-dose continuous infusion ceftazidime or aztreonam was used for the successful treatment of resistant systemic P. aeruginosa infections in 3 chronically immunocompromised patients.

CONCLUSIONS

Continuous infusion beta-lactam antibiotics are a potentially useful treatment strategy for resistant P. aeruginosa infections in immunocompromised patients.

Continuous-infusion beta-lactam antibiotics during continuous venovenous hemofiltration for the treatment of resistant gram-negative bacteria

OBJECTIVE

To describe the rationale, principles, and dosage calculations for continuous-infusion beta-lactam antibiotics to treat multidrug-resistant bacteria in patients undergoing continuous venovenous hemofiltration (CVVH).

DATA SOURCES

A MEDLINE search (1968-November 2008) of the English-language literature was performed using the terms continuous infusion and Pseudomonas or Acinetobacter; hemofiltration or CVVH or hemodiafiltration or CVVHDF or continuous renal replacement therapy or pharmacokinetics; and terms describing different beta-lactam antibiotics.

STUDY SELECTION AND DATA EXTRACTION

In vitro, in vivo, and human studies were evaluated that used continuous-infusion beta-lactam antibiotics to treat Pseudomonas aeruginosa and Acinetobacter baumannii infections. Studies were reviewed that described the pharmacokinetics of beta-lactam antibiotics during CVVH as well as other modalities of continuous renal replacement therapy.

DATA SYNTHESIS

Continuous infusion of beta-lactam antibiotics, maintaining drug concentrations 4-5 times higher than the minimum inhibitory concentration, is a promising approach for managing infections caused by P. aeruginosa and A. baumannii. Safe yet effective continuous infusion therapy is made difficult by the occurrence of acute renal failure and the need for renal replacement therapy. Case series and pharmacokinetic properties indicate that several beta-lactam antimicrobials that have been studied for continuous infusion, such as cefepime, ceftazidime, piperacillin, ticarcillin, clavulanic acid, and tazobactam, are significantly cleared by hemofiltration. Methodology and formulas are provided that allow practitioners to calculate dosage regimens and reach target drug concentrations for continuous beta-lactam antibiotic infusions during CVVH based on a literature review, pharmacokinetic principles, and our experience at the National Institutes of Health Clinical Center.

CONCLUSIONS

Continuous infusion of beta-lactam antibiotics may be a useful treatment strategy for multidrug-resistant gram-negative infections in the intensive care unit. Well-established pharmacokinetic and pharmacodynamic principles can be used to safely reach and maintain steady-state target concentrations of beta-lactam antibiotics in critical illness complicated by acute renal failure requiring CVVH.

Correlation of the Pharmacokinetic Parameters of Amikacin and Ceftazidime

BACKGROUND AND OBJECTIVES

Ceftazidime and amikacin are often prescribed concomitantly to treat infections caused by Gram-negative bacteria. Their physicochemical properties are quite similar. Both drugs are highly soluble in water, have low plasma protein binding and are >95% excreted unchanged by the kidney via glomerular filtration. Their pharmacokinetic parameters are therefore expected to correlate. This study was performed to explore the correlation between the pharmacokinetic parameters of these two drugs.

PATIENTS AND METHODS

Patients at Phramongkutklao Hospital, Bangkok, Thailand, who met the inclusion criteria participated in the study. They all received ceftazidime and amikacin concomitantly to treat their infections. After steady-state conditions had been reached, two blood samples were collected during the elimination phase of both drugs. Plasma drug concentrations were analysed and the pharmacokinetic parameters of each drug were calculated. The pharmacokinetic parameters that were examined included total drug clearance (CL), the elimination rate constant (k(e)), the elimination half life (t(1/2)) and the volume of distribution (V(d)). The correlations of the pharmacokinetic parameters of amikacin and ceftazidime were determined using regression analysis.

RESULTS

Regression analysis showed that the pharmacokinetic parameters of ceftazidime and amikacin were highly correlated. The correlation coefficients (r) of CL, k(e), t(1/2) and V(d) of the two drugs were 0.966, 0.943, 0.888 and 0.671, respectively. The correlation between amikacin clearance and ceftazidime clearance was higher than the correlation between either amikacin or ceftazidime clearance and creatinine clearance, for which the r values were 0.647 and 0.661, respectively.

CONCLUSIONS

The pharmacokinetic parameters of ceftazidime and amikacin were highly correlated. Knowledge of the pharmacokinetic parameters of one of these drugs can be used to predict the pharmacokinetic parameters of the other drug.

Clinical efficacy of continuous infusion of piperacillin compared with intermittent dosing in septic critically ill patients

Since the bactericidal effects of beta-lactam antibiotics are time dependent, the optimum strategy for their administration could be continuous infusion. In this prospective, randomised controlled trial to evaluate the clinical efficacy of continuous infusion therapy, we evaluated the outcomes for 40 septic critically ill patients who received piperacillin either continuously (2 g intravenously (i.v.) over 0.5 h as a loading dose followed by 8 g i.v. daily over 24 h (n=20)) or as an intermittent infusion (3 g i.v. every 6h over 0.5 h (n=20)). Results from our study demonstrated that the clinical efficacy of piperacillin as a continuous infusion is superior to intermittent administration in critically ill patients. Change in APACHE II scores from baseline at the end of the second, third and fourth days, respectively, were 4.1, 5.1 and 5.2 for continuous infusion and 2.0, 2.6 and 2.8 for intermittent infusion (P< or =0.04). Considering minimum inhibitory concentrations (MICs) of 16 microg/mL and 32 microg/mL, the percentage of time for which piperacillin plasma concentrations were higher than the MIC (%T>MIC) was calculated for each patient in the two groups. For MICs of 16 microg/mL and 32 microg/mL, %T>MIC in the continuous infusion group was 100% and 65% of the dosing interval, respectively; in the intermittent infusion group, %T>MIC was only 62% and 39% of the dosing interval. There was a significant relationship between clinical results and laboratory data. It was shown that the superiority of the clinical efficacy of continuous infusion could be related to piperacillin pharmacodynamics. Continuous infusion significantly reduced the severity of illness as demonstrated by APACHE II scores during therapy.

Time-kill curves as a tool for targeting ceftazidime serum concentration during continuous infusion for treatment of septicaemic melioidosis

Melioidosis is a fatal community-acquired infection endemic in tropical areas. Ten isolates of the causative microorganism were subjected to time-kill study using a range of ceftazidime concentrations. This study demonstrated that a ceftazidime concentration of eight times the minimum inhibitory concentration yielded an optimal bactericidal effect and should be the target concentration administered by continuous infusion.

Is there a pharmacodynamic need for the use of continuous versus intermittent infusion with ceftazidime against Pseudomonas aeruginosa? An in vitro pharmacodynamic model

OBJECTIVES

In order to explore the pharmacodynamic need for continuous versus intermittent (three times a day) administration of ceftazidime in critically ill patients, a pharmacokinetic computerized device was used to simulate concentrations of ceftazidime in human serum after 6 g/day.

METHODS

Efficacy was measured as the capability of simulated concentrations over time to reduce initial inoculum against four strains of Pseudomonas aeruginosa. MICs of the strains matched NCCLS breakpoints: one susceptible strain (MIC = 8 mg/L), two intermediate strains (MIC = 16 mg/L) and one resistant strain (MIC = 32 mg/L). C(max) was 119.97+/-2.53 mg/L for intermittent bolus and C(ss) (steady-state concentration) was 40.38+/-0.16 mg/L for continuous infusion. AUC(0-24) was similar for both regimens (approximately 950 mg x h/L). Inhibitory quotients were three times higher for the intermittent administration whereas t > MIC was higher for continuous infusion (100%) versus intermittent administration (99.8%, 69% and 47.6% for the susceptible, intermediate and resistant strains, respectively).

RESULTS

Against the susceptible and intermediate strains, no differences were found between both regimens with > or = 3 log10 reduction from 8 to 24 h. Against the resistant strain, only the continuous infusion achieved this bactericidal activity in the same time period, minimizing the differences between resistant and susceptible strains. Significantly higher initial inoculum reduction at 32 h was obtained for the continuous versus the intermittent administration (83.35% versus 38.40%, respectively).

CONCLUSIONS

These results stress the importance of optimizing t >MIC, even at peri-MIC concentrations, of ceftazidime against resistant strains. Local prevalence of resistance justifies, on a pharmacodynamic basis, electing for continuous infusion versus intermittent administration.