Pharmacokinetics and pharmacodynamics of intravenous levofloxacin in patients with early-onset ventilator-associated pneumonia

The expert clinical pharmacological advice program for tailoring on real-time antimicrobial therapies with emerging TDM candidates in special populations: how the ugly duckling turned into a swan

INTRODUCTION

The growing spread of infections caused by multidrug-resistant pathogens makes the need of tailoring antimicrobial therapies by means of a 'patient-centered' approach fundamental. In this scenario, therapeutic drug monitoring (TDM) of emerging antimicrobial candidates may be a valuable approach, but expert interpretation of TDM results should be granted for making them more clinically useful. The MD Clinical Pharmacologist may take over this task since this specialist may couple PK/PD expertise on drugs with a medical background and may provide expert interpretation of TDM results of antimicrobials for tailoring therapy on real-time in each single patient based on specific both drug/pathogen issues and patient issues.

AREAS COVERED

This article aims to highlight the main key-points and organizational aspects for implementing a successful TDM-based expert clinical pharmacological advice (ECPA) program for tailoring antimicrobial therapies on real-time in different hospitalized patient special populations.

EXPERT OPINION

TDM-based ECPA programs lead by the MD Clinical Pharmacologist may represent a way forward for maximizing clinical efficacy and for minimizing the risk of resistance developments and/or toxicity of antimicrobials. Stakeholders should be aware of the fact that this innovative approach may be cost-effective.

Green Automated Solid Phase Extraction to Measure Levofloxacin in Human Serum via Liquid Chromatography with Fluorescence Detection for Pharmacokinetic Study

A simple, selective, rapid, sensitive and less costly green automated solid phase extraction bio-analytical high-performance liquid chromatographic-based technique with fluorescence detection (Aut-SPE-BA-HPLC-FL) for the quantification of levofloxacin in human serum samples has been developed and validated. The serum samples were loaded into the chromatographic system without prior treatment and then injected into short (20 mm × 4.6 mm, 20 µm) protein-coated (PC) µBondapak CN (µBCN) silica pre-column (PC-µBCN-pre-column). Levofloxacin was retained and pre-concentrated on the head of the PC-µBCN-pre-column, while proteins and other polar components were eliminated using phosphate buffer saline (PBS), pH 7.4, as the first mobile phase in the extraction step. Levofloxacin is then transferred to the analytical column; ZORBAX Eclipse XDB-C18 (150 mm × 46 mm, 5 µm), through the aid of a column-switching valve technique, on-throughs the elution mode using the second mobile phase containing a methanol and phosphate buffer (0.05 M, pH 5) in a ratio of 70:30 (v/v). Levofloxacin signals were detected using a fluorescence detector operated at excitation/emission wavelengths of 295/500 nm. The proposed Aut-SPE-BA-HPLC-FL methodology showed linearity over a levofloxacin concentration range of 10–10,000 ng/mL (r2 = 0.9992), with good recoveries ranging from 87.12 to 97.55%. Because of the validation qualities in terms of linearity, recovery, precision, accuracy, selectivity and robustness, the Aut-SPE-BA-HPLC-FL method has been used in some clinical trials for therapeutic drug monitoring and the pharmacokinetic study of levofloxacin in human serum.

Clinical standards for the dosing and management of TB drugs

BACKGROUND: Optimal drug dosing is important to ensure adequate response to treatment, prevent development of drug resistance and reduce drug toxicity. The aim of these clinical standards is to provide guidance on 'best practice´ for dosing and management of TB drugs.METHODS: A panel of 57 global experts in the fields of microbiology, pharmacology and TB care were identified; 51 participated in a Delphi process. A 5-point Likert scale was used to score draft standards. The final document represents the broad consensus and was approved by all participants.RESULTS: Six clinical standards were defined: Standard 1, defining the most appropriate initial dose for TB treatment; Standard 2, identifying patients who may be at risk of sub-optimal drug exposure; Standard 3, identifying patients at risk of developing drug-related toxicity and how best to manage this risk; Standard 4, identifying patients who can benefit from therapeutic drug monitoring (TDM); Standard 5, highlighting education and counselling that should be provided to people initiating TB treatment; and Standard 6, providing essential education for healthcare professionals. In addition, consensus research priorities were identified.CONCLUSION: This is the first consensus-based Clinical Standards for the dosing and management of TB drugs to guide clinicians and programme managers in planning and implementation of locally appropriate measures for optimal person-centred treatment to improve patient care.

Methodological features of clinical pharmacokinetic-pharmacodynamic studies of antibacterials and antifungals: a systematic review

BACKGROUND

Pharmacokinetic (PK)-pharmacodynamic (PD) indices relate measures of drug exposure to antibacterial effect. Clinical PK-PD studies aim to correlate PK-PD indices with outcomes in patients. Optimization of dosing based on pre-clinical studies means that PK-PD relationships are difficult to establish; therefore studies need to be designed and reported carefully to validate pre-clinical findings.

OBJECTIVES

To describe the methodological features of clinical antibacterial and antifungal PK-PD studies that reported the relationship between PK-PD indices and clinical or microbiological responses.

METHODS

Studies published between 1980 and 2015 were identified through systematic searches. Methodological features of eligible studies were extracted.

RESULTS

We identified 85 publications containing 97 PK-PD analyses. Most studies were small, with fewer than 100 patients. Around a quarter were performed on patients with infections due to a single specific pathogen. In approximately one-third of studies, patients received concurrent antibiotics/antifungals and in some other studies patients received other treatments that may confound the PK-PD-outcome relationship. Most studies measured antimicrobial concentrations in blood/serum and only four measured free concentrations. Most performed some form of regression, time-to-event analysis or used the Hill/Emax equation to examine the association between PK-PD index and outcome. Target values of PK-PD indices that predict outcomes were investigated in 52% of studies. Target identification was most commonly done using recursive partitioning or logistic regression.

CONCLUSIONS

Given the variability in conduct and reporting, we suggest that an agreed set of standards for the conduct and reporting of studies should be developed.

Population pharmacokinetic modeling and clinical application of vancomycin in Chinese patients hospitalized in intensive care units

Management of vancomycin administration for intensive care units (ICU) patients remains a challenge. The aim of this study was to describe a population pharmacokinetic model of vancomycin for optimizing the dose regimen for ICU patients. We prospectively enrolled 466 vancomycin-treated patients hospitalized in the ICU, collected trough or approach peak blood samples of vancomycin and recorded corresponding clinical information from July 2015 to December 2017 at Tai Zhou Hospital of Zhejiang Province. The pharmacokinetics of vancomycin was analyzed by nonlinear mixed effects modeling with Kinetica software. Internal and external validation was evaluated by the maximum likelihood method. Then, the individual dosing regimens of the 92 patients hospitalized in the ICU whose steady state trough concentrations exceeded the target range (10–20 μg/ml) were adjusted by the Bayes feedback method. The final population pharmacokinetic model show that clearance rate (CL) of vancomycin will be raised under the conditions of dopamine combined treatment, severe burn status (Burn-S) and increased total body weight (TBW), but reduced under the conditions of increased serum creatinine (Cr) and continuous renal replacement therapy status; Meanwhile, the apparent distribution volume (V) of vancomycin will be enhanced under the terms of increased TBW, however decreased under the terms of increased age and Cr. The population pharmacokinetic parameters (CL and V) according to the final model were 3.16 (95%CI 2.83, 3.40) L/h and 60.71 (95%CI 53.15, 67.46). The mean absolute prediction error for external validation by the final model was 12.61% (95CI 8.77%, 16.45%). Finally, the prediction accuracy of 90.21% of the patients’ detected trough concentrations that were distributed in the target range of 10–20 μg/ml after dosing adjustment was found to be adequate. There is significant heterogeneity in the CL and V of vancomycin in ICU patients. The constructed model is sufficiently precise for the Bayesian dose prediction of vancomycin concentrations for the population of ICU Chinese patients.

Pharmacokinetics of Favipiravir in Critically Ill Patients With COVID-19

Since December 2019, a novel coronavirus (severe acute respiratory syndrome‐coronavirus 2 (SARS‐CoV‐2)) infection has been rapidly spreading worldwide and causing the respiratory illness, coronavirus disease 2019 (COVID‐19). The antiretroviral drug favipiravir (FPV) has been experimentally used for COVID‐19 treatment since March 2020 in Japan. However, the pharmacokinetics of FPV in critically ill patients is unknown. We measured the serum concentration of FPV using high‐performance liquid chromatography in patients with severe COVID‐19 who were admitted to the intensive care unit and placed on mechanical ventilation. The patients were administered 1,600 mg of FPV twice daily on day 1, followed by 600 mg twice daily from day 2 to day 5 (or more if needed). Suspensions of FPV tablets were administered through a nasogastric tube. Seven patients were enrolled in this study. Forty‐nine blood samples were obtained from the eligible patients to evaluate FPV concentration. The FPV trough (after 8–12 hours) concentrations of most samples were lower than the lower limit of quantification (1 µg/mL) and half‐maximal effective concentration (9.7 µg/mL) against SARS‐CoV‐2 previously tested in vitro. FPV trough concentration in critically ill patients was much lower than that of healthy subjects in a previous clinical trial, which is a cause for great concern. Further study is required to determine the optimal strategy for treatment of patients with severe COVID‐19.

Population Pharmacokinetics and Pharmacodynamics of Levofloxacin in Acutely Hospitalized Older Patients with Various Degrees of Renal Function

A retrospective study was conducted in a large sample of acutely hospitalized older patients who underwent therapeutic drug monitoring during levofloxacin treatment. The aim was to assess the population pharmacokinetics (popPK) and pharmacodynamics of levofloxacin among older patients. PopPK and Monte Carlo simulation were performed to define the permissible doses in older patients according to various degrees of renal function. Classification and regression tree (CART) analysis was used to detect the cutoff 24-hour area under the concentration-time curve (AUC24)/MIC ratio that best correlated with the clinical outcome. The probability of target attainment (PTA) of this value was calculated against different pathogens. A total of 168 patients were included, and 330 trough and 239 peak concentrations were used for the popPK analysis. Creatinine clearance (CrCL) was the only covariate that improved the model fit (levofloxacin CL = 0.399 + 0.051 × CrCLCKD-EPI [creatinine clearance estimated by means of the chronic kidney disease epidemiology]). Drug doses ranged between 500 mg every 48 h and 500 mg every 12 h in relation to different renal functions. The identified cutoff AUC24/MIC ratio (≥95.7) was the only covariate that correlated with a favorable clinical outcome in multivariate regression analysis (odds ratio [OR], 20.85; 95% confidence interval [CI], 1.56 to 186.73). PTAs were optimal (>80%) against Escherichia coli and Haemophilus influenzae, borderline against Staphylococcus aureus, and suboptimal against Pseudomonas aeruginosa The levofloxacin doses defined in our study may be effective for the treatment of infections due to bacterial pathogens, with an MIC of ≤0.5 mg/liter in older patients with various degrees of renal function, while minimizing the toxicity risk. Conversely, the addition of another active antimicrobial should be considered whenever treating infections caused by less susceptible pathogens.

Management of Adults With Hospital-acquired and Ventilator-associated Pneumonia: 2016 Clinical Practice Guidelines by the Infectious Diseases Society of America and the American Thoracic Society

It is important to realize that guidelines cannot always account for individual variation among patients. They are not intended to supplant physician judgment with respect to particular patients or special clinical situations. IDSA considers adherence to these guidelines to be voluntary, with the ultimate determination regarding their application to be made by the physician in the light of each patient's individual circumstances.These guidelines are intended for use by healthcare professionals who care for patients at risk for hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP), including specialists in infectious diseases, pulmonary diseases, critical care, and surgeons, anesthesiologists, hospitalists, and any clinicians and healthcare providers caring for hospitalized patients with nosocomial pneumonia. The panel's recommendations for the diagnosis and treatment of HAP and VAP are based upon evidence derived from topic-specific systematic literature reviews.

Therapeutic drug monitoring of anti-infective agents in critically ill patients

Initial adequate anti-infective therapy is associated with significantly improved clinical outcomes for patients with severe infections. However, in critically ill patients, several pathophysiological and/or iatrogenic factors may affect the pharmacokinetics of anti-infective agents leading to suboptimal drug exposure, in particular during the early phase of therapy. Therapeutic drug monitoring (TDM) may assist to overcome this problem. We discuss the available evidence on the use of TDM in critically ill patient populations for a number of anti-infective agents, including aminoglycosides, β-lactams, glycopeptides, antifungals and antivirals. Also, we present the available evidence on the practices of anti-infective TDM and describe the potential utility of TDM to improve treatment outcome in critically ill patients with severe infections. For aminoglycosides, glycopeptides and voriconazole, beneficial effects of TDM have been established on both drug effectiveness and potential side effects. However, for other drugs, therapeutic ranges need to be further defined to optimize treatment prescription in this setting.

Does Critical Illness Change Levofloxacin Pharmacokinetics?

Levofloxacin is commonly used in critically ill patients for which existing data suggest nonstandard dosing regimens should be used. The objective of this study was to compare the population pharmacokinetics of levofloxacin in critically ill and in non-critically ill patients. Adult patients with a clinical indication for levofloxacin were eligible for participation in this prospective pharmacokinetic study. Patients were given 500 mg or 750 mg daily by intravenous administration with up to 11 blood samples taken on day 1 or 2 of therapy. Plasma samples were analyzed and population pharmacokinetic analysis was undertaken using Pmetrics. Thirty-five patients (18 critically ill) were included. The mean (standard deviation [SD]) age, weight, and Cockcroft-Gault creatinine clearance for the critically ill and for the non-critically ill patients were 60.3 (16.4) and 72.0 (11.6) years, 78.5 (14.8) and 70.9 (15.8) kg, and 71.9 (65.8) and 68.2 (30.1) ml/min, respectively. A two-compartment linear model best described the data. Increasing creatinine clearance was the only covariate associated with increasing drug clearance. The presence of critical illness did not significantly affect any pharmacokinetic parameter. The mean (SD) parameter estimates were as follows: clearance, 8.66 (3.85) liters/h; volume of the central compartment (Vc), 41.5 (24.5) liters; intercompartmental clearance constants from central to peripheral, 2.58 (3.51) liters/h; and peripheral to central compartments, 0.90 (0.58) liters/h. Monte Carlo dosing simulations demonstrated that achievement of therapeutic exposures was dependent on renal function, pathogen, and MIC. Critical illness appears to have no independent effect on levofloxacin pharmacokinetics that cannot be explained by altered renal function.

Personalized therapeutics for levofloxacin: a focus on pharmacokinetic concerns

Background

Personalized medicine should be encouraged because patients are complex, and this complexity results from biological, medical (eg, demographics, genetics, polypharmacy, and multimorbidities), socioeconomic, and cultural factors. Levofloxacin (LVX) is a broad-spectrum fluoroquinolone antibiotic. Awareness of personalized therapeutics for LVX seems to be poor in clinical practice, and is reflected in prescribing patterns. Pharmacokinetic–pharmacodynamic studies have raised concerns about suboptimal patient outcomes with the use of LVX for some Gram-negative infections. Meanwhile, new findings in LVX therapeutics have only been sporadically reported in recent years. Therefore, an updated review on personalized LVX treatment with a focus on pharmacokinetic concerns is necessary.

Methods

Relevant literature was identified by performing a PubMed search covering the period from January 1993 to December 2013. We included studies describing dosage adjustment and factors determining LVX pharmacokinetics, or pharmacokinetic–pharmacodynamic studies exploring how best to prevent the emergence of resistance to LVX. The full text of each included article was critically reviewed, and data interpretation was performed.

Results

In addition to limiting the use of fluoroquinolones, measures such as reducing the breakpoints for antimicrobial susceptibility testing, choice of high-dose short-course of once-daily LVX regimen, and tailoring LVX dose in special patient populations help to achieve the validated pharmacokinetic–pharmacodynamic target and combat the increasing LVX resistance. Obese individuals with normal renal function cleared LVX more efficiently than normal-weight individuals. Compared with the scenario in healthy subjects, standard 2-hour spacing of calcium formulations and oral LVX was insufficient to prevent a chelation interaction in cystic fibrosis patients. Inconsistent conclusions were derived from studies of the influence of sex on the pharmacokinetics of LVX, which might be associated with sample size and administration route. Children younger than 5 years cleared LVX nearly twice as fast as adults. Patients in intensive care receiving LVX therapy showed significant pharmacokinetic differences compared with healthy subjects. Creatinine clearance explained most of the population variance in the plasma clearance of LVX. Switching from intravenous to oral delivery of LVX had economic benefits. Addition of tamsulosin to the LVX regimen was beneficial for patients with bacterial prostatitis because tamsulosin could increase the maximal concentration of LVX in prostatic tissue. Coadministration of multivalent cation-containing drugs and LVX should be avoided. For patients receiving warfarin and LVX concomitantly, caution is needed regarding potential changes in the international normalized ratio; however, it is unnecessary to seek alternatives to LVX for the sake of avoiding drug interaction with warfarin. It is unnecessary to proactively reduce the dose of cyclosporin or tacrolimus when comedicated with LVX. Transporters such as organic anion-transporting polypeptide 1A2, P-glycoprotein, human organic cation transporter 1, and multidrug and toxin extrusion protein 1 are involved in the pharmacokinetics of LVX.

Conclusion

Personalized LVX therapeutics are necessary for the sake of better safety, clinical success, and avoidance of resistance. New findings regarding individual dosing of LVX in special patient populations and active transport mechanisms in vivo are opening up new horizons in clinical practice.

Optimal dosing of antibiotics in critically ill patients by using continuous/extended infusions: a systematic review and meta-analysis

Introduction

The aim of this study was to determine whether using pharmacodynamic-based dosing of antimicrobials, such as extended/continuous infusions, in critically ill patients is associated with improved outcomes as compared with traditional dosing methods.

Methods

We searched Medline, HealthStar, EMBASE, Cochrane Clinical Trial Registry, and CINAHL from inception to September 2013 without language restrictions for studies comparing the use of extended/continuous infusions with traditional dosing. Two authors independently selected studies, extracted data on methodology and outcomes, and performed quality assessment. Meta-analyses were performed by using random-effects models.

Results

Of 1,319 citations, 13 randomized controlled trials (RCTs) (n = 782 patients) and 13 cohort studies (n = 2,117 patients) met the inclusion criteria. Compared with traditional non-pharmacodynamic-based dosing, RCTs of continuous/extended infusions significantly reduced clinical failure rates (relative risk (RR) 0.68; 95% confidence interval (CI) 0.49 to 0.94, P = 0.02) and intensive care unit length of stay (mean difference, −1.5; 95% CI, −2.8 to −0.2 days, P = 0.02), but not mortality (RR, 0.87; 95% CI, 0.64 to 1.19; P = 0.38). No significant between-trial heterogeneity was found for these analyses (I² = 0). Reduced mortality rates almost achieved statistical significance when the results of all included studies (RCTs and cohort studies) were pooled (RR, 0.83; 95% CI, 0.69 to 1.00; P = 0.054).

Conclusions

Pooled results from small RCTs suggest reduced clinical failure rates and intensive care unit length-of-stay when using continuous/extended infusions of antibiotics in critically ill patients. Reduced mortality rates almost achieved statistical significance when the results of RCTs were combined with cohort studies. These results support the conduct of adequately powered RCTs to define better the utility of continuous/extended infusions in the era of antibiotic resistance.

Gender analysis of moxifloxacin clinical trials

PURPOSE

To determine the inclusion of women and the sex-stratification of results in moxifloxacin Clinical Trials (CTs), and to establish whether these CTs considered issues that specifically affect women, such as pregnancy and use of hormonal therapies. Previous publications about women's inclusion in CTs have not specifically studied therapeutic drugs. Although this type of drug is taken by men and women at a similar rate, adverse effects occur more frequently in the latter.

METHODS

We reviewed 158 published moxifloxacin trials on humans, retrieved from MedLine and the Cochrane Library (1998-2010), to determine whether they complied with the gender recommendations published by U.S. Food and Drug Administration Guideline.

RESULTS

Of a total of 80,417 subjects included in the moxifloxacin CTs, only 33.7% were women in phase I, in contrast to phase II, where women accounted for 45%, phase III, where they represented 38.3% and phase IV, where 51.3% were women. About 40.9% (n=52) of trials were stratified by sex and 15.3% (n=13) and 9% (n=7) provided data by sex on efficacy and adverse effects, respectively. We found little information about the influence of issues that specifically affect women. Only 3 of the 59 journals that published the moxifloxacin CTs stated that authors should stratify their results by sex.

CONCLUSIONS

Women are under-represented in the published moxifloxacin trials, and this trend is more marked in phase I, as they comprise a higher proportion in the other phases. Data by sex on efficacy and adverse effects are scarce in moxifloxacin trials. These facts, together with the lack of data on women-specific issues, suggest that the therapeutic drug moxifloxacin is only a partially evidence-based medicine.

Pharmacokinetics of moxifloxacin and high-dose levofloxacin in severe lower respiratory tract infections

This study evaluated the pharmacokinetics of intravenous moxifloxacin 400 mg once and levofloxacin 500 mg twice daily in patients with lower respiratory tract infections (LRTIs) and assessed their pharmacodynamic adequacy against common respiratory pathogens. Eighteen patients with LRTIs hospitalised in general wards were included. Serial blood samples were obtained at steady state and concentrations were determined using HPLC. Pharmacokinetic variables were estimated by a two-compartment model. The characteristic pharmacodynamic parameter for fluoroquinolones (AUC(0-24)/MIC) was calculated. Peak and trough concentrations were, respectively, 4.81 ± 1.03 and 0.59 ± 1.13 mg/L for moxifloxacin and 6.42 ± 1.08 and 0.79 ± 0.39 mg/L for levofloxacin. Pharmacokinetic data for moxifloxacin and levofloxacin, respectively, were: CL, 10.27 ± 1.24 and 22.66 ± 6.62 L/h; t1/2, 13.43 ± 5.12 and 6.75 ± 1.34 h; Vss, 163.03 ± 53.88 and 170.73 ± 39.59 L; and AUC(0-24), 39.38 ±5.28 and 47.06 ± 14.09 mg·h/L. The pharmacodynamic target was attained in all patients by both antibiotics against the majority of respiratory pathogens. Moxifloxacin proved to be pharmacodynamically efficacious against Gram-positive bacteria with MICs ≤ 0.79 mg/L and Gram-negative bacteria with MICs ≤ 0.32 mg/L. These MIC thresholds for levofloxacin were 1.1 mg/L and 0.38 mg/L, respectively. Moxifloxacin and high-dose levofloxacin show a favourable pharmacokinetic profile in plasma of patients with severe LRTIs, without significant interpatient variability. They ensure optimal pharmacodynamic exposure against the majority of microbes involved in these infections. However, the predicted efficacy against Gram-negative bacteria with MICs ≥ 0.5 mg/L appears to be low.

Pharmacokinetics and pharmacodynamics of ciprofloxacin in critically ill patients after the first intravenous administration of 400 mg

PURPOSE

To investigate the pharmacokinetics and pharmacodynamics of ciprofloxacin in critically ill patients after the first intravenous administration of 400 mg.

MATERIAL/METHODS

Plasma concentrations were measured in 20 critically ill patients (mean [SD]; age, 55.5 [16.5] years; weight, 80.3 [16.9] kg; and creatinine clearance, 110.0 [71.5] mL/min). Four blood samples were drawn at the following time points 0, 0.5, 6 , 8 hours after infusion. Ciprofloxacin concentrations were determined by high-performance liquid chromatography.

RESULTS

In the cases where ciprofloxacin was applied in targeted antibiotic therapy the minimum inhibitory concentrations (MIC) were ≤0.5 mg/l. The maximum and minimum plasma concentrations of ciprofloxacin were 1.74 (0.58-7.90) and 0.45 (0.16-2.96) mg/l, respectively. The main pharmacokinetic parameters for ciprofloxacin in the analyzed patients were as follows: k(el), 0.21 h-1; t(1/2kel), 3.37 h; AUC(0-inf), 10.10 mg×h/l; AUMC(0-last), 15.36 mg×h(2)/l; MRT, 1.71 h; V(d), 214.8 l; Cl, 39.70 l/h. Considering the maximum value of MIC (0.5 mg/l) only 30% and 25% of analyzed patients had desired values of the PK/PD indexes AUIC>125 and C(max) /MIC>10, respectively.

CONCLUSIONS

The target plasma concentrations after the first dose of ciprofloxacin were reached only in a few critically ill patients. Considerable inter-subject variability for PK/PD parameters in ICU patients requires systematic monitoring.

Management of antimicrobial use in the intensive care unit

Critically ill patients admitted to the intensive care unit (ICU) are frequently treated with antimicrobials. The appropriate and judicious use of antimicrobial treatment in the ICU setting is a constant clinical challenge for healthcare staff due to the appearance and spread of new multiresistant pathogens and the need to update knowledge of factors involved in the selection of multiresistance and in the patient's clinical response. In order to optimize the efficacy of empirical antibacterial treatments and to reduce the selection of multiresistant pathogens, different strategies have been advocated, including de-escalation therapy and pre-emptive therapy as well as measurement of pharmacokinetic and pharmacodynamic (pK/pD) parameters for proper dosing adjustment. Although the theoretical arguments of all these strategies are very attractive, evidence of their effectiveness is scarce. The identification of the concentration-dependent and time-dependent activity pattern of antimicrobials allow the classification of drugs into three groups, each group with its own pK/pD characteristics, which are the basis for the identification of new forms of administration of antimicrobials to optimize their efficacy (single dose, loading dose, continuous infusion) and to decrease toxicity. The appearance of new multiresistant pathogens, such as imipenem-resistant Pseudomonas aeruginosa and/or Acinetobacter baumannii, carbapenem-resistant Gram-negative bacteria harbouring carbapenemases, and vancomycin-resistant Enterococcus spp., has determined the use of new antibacterials, the reintroduction of other drugs that have been removed in the past due to toxicity or the use of combinations with in vitro synergy. Finally, pharmacoeconomic aspects should be considered for the choice of appropriate antimicrobials in the care of critically ill patients.

Pharmacokinetics of intravenous levofloxacin administered at 750 milligrams in obese adults

The physiochemical properties of levofloxacin suggest that it is an agent which may exhibit altered pharmacokinetics in obese individuals. The purpose of this study was to describe the pharmacokinetics of a single 750-mg intravenous dose of levofloxacin in both hospitalized and ambulatory obese individuals. The hypothesis was that a standard dose of levofloxacin in obese individuals would achieve serum concentrations likely to be therapeutic. A single levofloxacin dose of 750 mg was infused over 90 min, and seven serial serum samples were subsequently obtained to evaluate the pharmacokinetics after the first dose. The peak concentrations of levofloxacin were comparable to those seen with normal-weight individuals. However, the area under the concentration-time curve and clearance were quite variable. Accelerated clearance was evident in the ambulatory obese individuals. Further investigation of the effects of obesity on the pharmacokinetics of levofloxacin is necessary to ensure optimal dosing.

Impact of recA on levofloxacin exposure-related resistance development

Genetic mutations are one of the major mechanisms by which bacteria acquire drug resistance. One of the known mechanisms for inducing mutations is the SOS response system. We investigated the effect of disrupting recA, an inducer of the SOS response, on resistance development using an in vitro hollow-fiber infection model. A clinical Staphylococcus aureus isolate and a laboratory wild-type strain of Escherichia coli were compared to their respective recA-deleted isogenic daughter isolates. Approximately 2 × 10(5) CFU/ml of bacteria were subjected to escalating levofloxacin exposures for up to 120 h. Serial samples were obtained to ascertain simulated drug exposures and total and resistant bacterial burdens. Quinolone resistance determining regions of gyrA and grlA (parC for E. coli) in levofloxacin-resistant isolates were sequenced to confirm the mechanism of resistance. The preexposure MICs of the recA-deleted isolates were 4-fold lower than those of their respective parents. In S. aureus, a lower area under the concentration-time curve over 24 h at steady state divided by the MIC (AUC/MIC) was required to suppress resistance development in the recA-deleted mutant (an AUC/MIC of >23 versus an AUC/MIC of >32 was necessary in the mutant versus the parent isolate, respectively), and a prominent difference in the total bacterial burden was observed at 72 h. Using an AUC/MIC of approximately 30, E. coli resistance emergence was delayed by 24 h in the recA-deleted mutant. Diverse mutations in gyrA were found in levofloxacin-resistant isolates recovered. Disruption of recA provided additional benefits apart from MIC reduction, attesting to its potential role for pharmacologic intervention. The clinical relevance of our findings warrants further investigations.

Bench-to-bedside review: Appropriate antibiotic therapy in severe sepsis and septic shock--does the dose matter?

Appropriate antibiotic therapy in patients with severe sepsis and septic shock should mean prompt achievement and maintenance of optimal exposure at the infection site with broad-spectrum antimicrobial agents administered in a timely manner. Once the causative pathogens have been identified and tested for in vitro susceptibility, subsequent de-escalation of antimicrobial therapy should be applied whenever feasible. The goal of appropriate antibiotic therapy must be pursued resolutely and with continuity, in view of the ongoing explosion of antibiotic-resistant infections that plague the intensive care unit setting and of the continued decrease in new antibiotics emerging. This article provides some principles for the correct handling of antimicrobial dosing regimens in patients with severe sepsis and septic shock, in whom various pathophysiological conditions may significantly alter the pharmacokinetic behaviour of drugs.

Pharmacokinetic issues for antibiotics in the critically ill patient

OBJECTIVE

To discuss the altered pharmacokinetic properties of selected antibiotics in critically ill patients and to develop basic dose adjustment principles for this patient population.

DATA SOURCES

PubMed, EMBASE, and the Cochrane-Controlled Trial Register.

STUDY SELECTION

Relevant papers that reported pharmacokinetics of selected antibiotic classes in critically ill patients and antibiotic pharmacodynamic properties were reviewed. Antibiotics and/or antibiotic classes reviewed included aminoglycosides, beta-lactams (including carbapenems), glycopeptides, fluoroquinolones, tigecycline, linezolid, lincosamides, and colistin.

DATA SYNTHESIS

Antibiotics can be broadly categorized according to their solubility characteristics which can, in turn, help describe possible altered pharmacokinetics that can be caused by the pathophysiological changes common to critical illness. Hydrophilic antibiotics (e.g., aminoglycosides, beta-lactams, glycopeptides, and colistin) are mostly affected with the pathphysiological changes observed in critically ill patients with increased volumes of distribution and altered drug clearance (related to changes in creatinine clearance). Lipophilic antibiotics (e.g., fluoroquinolones, macrolides, tigecycline, and lincosamides) have lesser volume of distribution alterations, but may develop altered drug clearances. Using antibiotic pharmacodynamic bacterial kill characteristics, altered dosing regimens can be devised that also account for such pharmacokinetic changes.

CONCLUSIONS

Knowledge of antibiotic pharmacodynamic properties and the potential altered antibiotic pharmacokinetics in critically ill patients can allow the intensivist to develop individualized dosing regimens. Specifically, for renally cleared drugs, measured creatinine clearance can be used to drive many dose adjustments. Maximizing clinical outcomes and minimizing antibiotic resistance using individualized doses may be best achieved with therapeutic drug monitoring.

Pharmacokinetics/pharmacodynamics of antibacterials in the Intensive Care Unit: setting appropriate dosing regimens

Patients admitted to Intensive Care Units (ICUs) are at very high risk of developing severe nosocomial infections. Consequently, antimicrobials are among the most important and commonly prescribed drugs in the management of these patients. Critically ill patients in ICUs include representatives of all age groups with a range of organ dysfunction related to severe acute illness that may complicate long-term illness. The range of organ dysfunction, together with drug interactions and other therapeutic interventions (e.g. haemodynamically active drugs and continuous renal replacement therapies), may strongly impact on antimicrobial pharmacokinetics in critically ill patients. In the last decade, it has become apparent that the intrinsic pharmacokinetic (PK) and pharmacodynamic (PD) properties are the major determinants of in vivo efficacy of antimicrobial agents. PK/PD parameters are essential in facilitating the translation of microbiological activity into clinical situations, ensuring a successful outcome. In this review, we analyse the typical patterns of antimicrobial activity and the corresponding PK/PD parameters, with a special focus on a PK/PD dosing approach of the antimicrobial agent classes commonly utilised in the ICU setting.

Pharmacokinetics and pharmacodynamics of levofloxacin in critically ill patients with ventilator-associated pneumonia

The pharmacokinetics of levofloxacin and outcome of levofloxacin therapy in critically ill patients with ventilator-associated pneumonia (VAP) were assessed. Further theoretical considerations regarding the pharmacokinetic/pharmacodynamic (PK/PD) appropriateness of levofloxacin therapy were made. Twelve patients completed the study, all of whom were treated with a standard intravenous levofloxacin regimen (2x500 mg on Day 1, then 1x500 mg daily). The maximum free plasma levofloxacin concentration (fC(max,ss)) and the area under the free concentration-time curve (fAUC) were 8.13+/-1.64 mg/L and 49.63+/-15.60 mgh/L, respectively. Optimal PK/PD target parameters were achieved in 10 patients; clinical success was attained in 11 of the 12 patients who completed the study. Bacterial eradication was obtained in 9 of the 11 cases with microbiologically confirmed bacteriological aetiology. Intravenous levofloxacin therapy (500 mg/day) was proven to be an effective regimen in this limited number of patients with VAP. However, theoretical considerations based on PK/PD indices predict that, with the current susceptibility breakpoint of 2mg/L, even higher levofloxacin doses (e.g. 1000 mg) could result in treatment failures in infections caused by pathogens labelled as levofloxacin-susceptible in the microbiology report.

Modeling of microbial population responses to time-periodic concentrations of antimicrobial agents

We present the development and first experimental validation of a mathematical modeling framework for predicting the eventual response of heterogeneous (distributed-resistance) microbial populations to antimicrobial agents at time-periodic (hence pharmacokinetically realistic) concentrations. Our mathematical model predictions are validated in a hollow-fiber in vitro experimental infection model. They are in agreement with the threshold levofloxacin exposure necessary to suppress resistance development of Pseudomonas aeruginosa in a murine thigh infection model. Predictions made by the proposed mathematical modeling framework can offer guidance for targeted testing of promising regimens. This can aid the development and clinical use of antimicrobial agents that combat microbial resistance.

Levofloxacin in the treatment of ventilator-associated pneumonia

The use of levofloxacin in critically ill patients has progressively increased since commercial marketing of the drug in 1999, despite the fact that few studies have been designed to assess the use of levofloxacin in this population. Pharmacological characteristics, broad spectrum of activity, and tolerability account for the high interest in the drug for the treatment of different infectious diseases, including ventilator-associated pneumonia (VAP), and the recommendation of levofloxacin in guidelines developed by a number of scientific societies. According to pharmacokinetic-pharmacodynamic data, it seems reasonable to assume that an increase in activity follows from a larger dose, so that 500 mg/12 h is adequate in patients with VAP. In critically ill patients with VAP, levofloxacin monotherapy is indicated for empirical treatment of patients with early onset pneumonia without risk factors for multiresistant pathogens, and in combination therapy for late onset VAP or for patients at risk for multiresistant pathogens. The use of levofloxacin in combination therapy is supported by multiple reasons, including: increased empirical coverage in infections with suspected intracellular pathogens; substitution for more toxic antimicrobial agents (e.g., aminoglycosides) in patients with renal dysfunction and in those at risk for renal insufficiency; and severity of systemic response to infection (septic shock) that justifies multiple treatment with better tolerated antibiotics. The availability of the oral formulation allows sequential therapy, switching from the intravenous route to the oral route. Levofloxacin is well tolerated by critically ill patients, with few adverse events of mild to moderate severity.

The antimicrobial therapy puzzle: could pharmacokinetic-pharmacodynamic relationships be helpful in addressing the issue of appropriate pneumonia treatment in critically ill patients?

Until recently, the in vitro susceptibility of microorganisms was considered the only fundamental aspect for antibiotic efficacy in treating pneumonia. However, the relevance of pharmacokinetic-pharmacodynamic relationships in optimizing drug exposure has been progressively highlighted. Antimicrobial agents were divided into concentration-dependent or time-dependent groups, with the most consistently relevant pharmacodynamic parameters for efficacy being either the ration of the plasma peak concentration to the minimum inhibitory concentration or the time the plasma concentration persists above the minimum inhibitory concentration of the etiological agent, respectively. For the adequate treatment of pneumonia, optimal pharmacodynamic exposure should be ensured also at the infection site. To investigate this, a methodologically correct approach may be to detect drug concentration levels in the epithelial lining fluid and in the alveolar macrophages for extracellular and intracellular pathogens, respectively. From this perspective, the pharmacokinetic factors--only in some instances--support the achievement of optimal exposure during the treatment of pneumonia with fixed standard dosing regimens of antimicrobials; conversely, in other instances, the pharmacokinetic factors suggest the need for an implemented dosage regimen or even the choice of a different drug.

Antimicrobial therapy in critically ill patients: a review of pathophysiological conditions responsible for altered disposition and pharmacokinetic variability

Antimicrobials are among the most important and commonly prescribed drugs in the management of critically ill patients. Selecting the appropriate antimicrobial at the commencement of therapy, both in terms of spectrum of activity and dose and frequency of administration according to concentration or time dependency, is mandatory in this setting. Despite appropriate standard dosage regimens, failure of the antimicrobial treatment may occur because of the inability of the antimicrobial to achieve adequate concentrations at the infection site through alterations in its pharmacokinetics due to underlying pathophysiological conditions. According to the intrinsic chemicophysical properties of antimicrobials, hydrophilic antimicrobials (beta-lactams, aminoglycosides, glycopeptides) have to be considered at much higher risk of inter- and intraindividual pharmacokinetic variations than lipophilic antimicrobials (macrolides, fluoroquinolones, tetracyclines, chloramphenicol, rifampicin [rifampin]) in critically ill patients, with significant frequent fluctuations of plasma concentrations that may require significant dosage adjustments. For example, underexposure may occur because of increased volume of distribution (as a result of oedema in sepsis and trauma, pleural effusion, ascites, mediastinitis, fluid therapy or indwelling post-surgical drainage) and/or enhanced renal clearance (as a result of burns, drug abuse, hyperdynamic conditions during sepsis, acute leukaemia or use of haemodynamically active drugs). On the other hand, overexposure may occur because of a drop in renal clearance caused by renal impairment. Care with all these factors whenever choosing an antimicrobial may substantially improve the outcome of antimicrobial therapy in critically ill patients. However, since these situations may often coexist in the same patient and pharmacokinetic variability may be unpredictable, the antimicrobial policy may further benefit from real-time application of therapeutic drug monitoring, since this practice, by tailoring exposure to the individual patient, may consequently be helpful both in improving the outcome of antimicrobial therapy and in containing the spread of resistance in the hospital setting.

Pharmacokinetics of levofloxacin after single intravenous and repeat oral administration to cats

The pharmacokinetic properties of the fluoroquinolone levofloxacin, were investigated in five cats after single intravenous and repeat oral administration at a daily dose of 10 mg/kg. Levofloxacin serum concentration was analyzed by microbiological assay using Klebsiella pneumoniae ATCC 10031 as test microorganism. Serum levofloxacin disposition after intravenous and oral dosing was best fitted to a bicompartmental and a monocompartmental open models with first-order elimination, respectively. After intravenous administration, distribution was rapid (t(1/2(d)) 0.26 +/- 0.18 h) and wide as reflected by the steady-state volume of distribution of 1.75 +/- 0.42 L/kg. Drug elimination was slow with a total body clearance of 0.14 +/- 0.04 L/h.kg and a t(1/2) for this process of 9.31 +/- 1.63 h. The mean residence time was of 12.99 +/- 2.12 h. After repeat oral administration, absorption half-life was of 0.18 +/- 0.12 h and Tmax of 1.62 +/- 0.84 h. The bioavailability was high (86.27 +/- 43.73%) with a peak plasma concentration at the steady state of 4.70 +/- 0.91 microg/mL. Drug accumulation was not significant after four oral administrations. Estimated efficacy predictors for levofloxacin after either intravenous or oral administration indicate a good profile against bacteria with a MIC value below of 0.5 microg/mL. However, for microorganisms with MIC values of 1 microg/mL it would be efficacious only when administered intravenously.

Levofloxacin disposition over time in aqueous humor of patients undergoing cataract surgery

The ocular disposition of levofloxacin in patients receiving two 500-mg oral doses 10 h apart before cataract surgery was assessed with the intent of defining drug ocular exposure over time. The mean aqueous humor concentrations persisted above 1.5 mg/liter between 1.5 and 6.0 h after the second dose, with average aqueous-to-plasma ratios ranging between 0.33 and 0.57. This favorable ocular disposition provides support for trials of systemic levofloxacin for prophylaxis of postoperative endophthalmitis in selected patients or as adjunctive therapy for the treatment of this potentially devastating infective complication.

Pharmacokinetics and intrapulmonary diffusion of levofloxacin in critically ill patients with severe community-acquired pneumonia

OBJECTIVE

To determine the steady-state plasma and epithelial lining fluid concentrations of intravenous levofloxacin, 500 mg, administered once or twice daily in critically ill patients with severe community-acquired pneumonia.

DESIGN

Prospective, open-label study.

SETTING

An intensive care unit and a clinical pharmacokinetic laboratory in two university hospitals.

PATIENTS

Twenty-four adult patients with severe community-acquired pneumonia and receiving mechanical ventilation were enrolled.

INTERVENTIONS

All subjects received 1-hr intravenous infusions of 500 mg levofloxacin once or twice daily. The plasma and epithelial lining fluid levofloxacin concentrations were determined at steady-state after 2 days of therapy with high-performance liquid chromatography.

MEASUREMENTS AND MAIN RESULTS

The median (interquartile range [IQR]) plasma and epithelial lining fluid peak levofloxacin concentrations were 12.6 (IQR, 12.0-14.1) and 11.9 (IQR, 8.7-13.7) mg/L, respectively, in the once-daily group and 19.7 (IQR, 19.0-22.0) and 17.8 (IQR, 16.2-23.5) mg/L in the twice-daily group, showing a pulmonary percentage penetration of >100% in both groups. The median (IQR) total body exposures were 151 (IQR, 137-174) and 416 (IQR, 406-472) mg.hr/L, respectively, in the once-daily and twice-daily groups.

CONCLUSIONS

Our results suggest that in critically ill patients who are receiving mechanical ventilation and have severe community-acquired pneumonia and creatinine clearance of >40 mL/min, the administration of 500 mg of intravenous levofloxacin once and twice daily allows for the exceeding of pharmacodynamic thresholds predictive of outcome (i.e., peak concentration to minimum inhibitory concentration ratio of >10 or area under concentration-time curve to minimal inhibitory concentration ratio of >125 hrs) both in serum and epithelial lining fluid for pathogens with minimum inhibitory concentration values of < or =1 mg/L and >1 mg/L, respectively.

Urinary pharmacokinetics and theoretical pharmacodynamics of intravenous levofloxacin in intensive care unit patients treated with 500 mg b.i.d. for ventilator-associated pneumonia

This study assessed the urinary pharmacokinetics and theoretical pharmacodynamics of levofloxacin in ICU patients treated with 500 mg b.i.d. i.v. for ventilator associated pneumonia to evaluate if this high dosage regimen might ensure appropriate exposure in the treatment of severe UTIs in ICU patients. Nineteen patients (11M, 8F; age, 52 +/- 21 years; weight, 75 +/- 16 kg) presenting with normal renal function (estimated creatinine clearance, 1.83 +/- 0.61 ml/min/kg; diuresis, 1709 +/- 643ml / 24h) were assessed. In steady-state conditions, urine samples were collected at 0-2h, 2-4h, 4-8h and 8-12h during a dosing interval, and urinary concentrations of levofloxacin were assayed by HPLC. Mean (+/- SD) levofloxacin urinary concentrations were 329.1 +/- 159.9, 388.6 +/- 143.5, 266.0 +/- 102.8 and 168.1 +/- 93.3mg/L at 0-2h, 2-4h, 4-8h and 8-12h, respectively, with urinary AUC0-tau of 3171.4 +/- 1192.1mg/L x h. Mean (+/- SD) levofloxacin excretion rates were 44.1 +/- 20.7, 42.8 +/- 8.2, 31.7 +/- 5.8 and 19.8 +/- 4.2 mg/h during the 0-2h, 2-4, 4-8h and 8-12h interval, respectively. Our findings suggest that, consistently with levofloxacin showing high renal excretion as unmodified drug, 500mg b.i.d. i.v. of levofloxacin ensure and maintain urinary concentrations at least 50-fold higher than the MIC90 of most sensitive uropathogens during the overall dosing interval in ICU patients with normal renal function. Considering the major pharmacodynamic determinants for the concentration-dependent bactericidal activity of levofloxacin as applicable at the urinary level (CU/MIC of >12.2 and/or AUC24h U /MIC of >125h), this high dosage regimen may ensure optimal exposure for the treatment of catheter-related and severe lower UTIs not only against sensitive microorganisms, but probably also whenever microorganisms usually considered as intermediate susceptible or resistant to levofloxacin may be involved.

Levofloxacin disposition in cerebrospinal fluid in patients with external ventriculostomy

In vitro levofloxacin exhibits both potent or intermediate activity against most of the pathogens frequently responsible for acute bacterial meningitis and synergistic activity with some beta-lactams. Since levofloxacin was shown to penetrate the cerebrospinal fluid (CSF) during meningeal inflammation both in animals and in humans, the disposition of levofloxacin in CSF was studied in 10 inpatients with external ventriculostomy because of communicating hydrocephalus related to subarachnoid occlusion due to cerebral accidents who were treated with 500 mg of levofloxacin intravenously twice a day because of extracerebral infections. Plasma and CSF concentration-time profiles and pharmacokinetics were assessed at steady state. Plasma and CSF levofloxacin concentrations were analyzed by high-pressure liquid chromatography. The peak concentration of levofloxacin at steady state (C(max ss))was 10.45 mg/liter in plasma and 4.06 mg/liter in CSF, respectively, with the ratio of the C(max ss) in CSF to the C(max ss) in plasma being 0.47. The areas under the concentration-time curves during the 12-h dosing interval (AUC(0-tau)s) were 47.69 mg. h/liter for plasma and 33.42 mg. h/liter for CSF, with the ratio of the AUC(0-tau) for CSF to the AUC(0-tau) for plasma being 0.71. The terminal-phase half-life of levofloxacin in CSF was longer than that in plasma (7.02 +/- 1.57 and 5.51 +/- 1.36 h, respectively; P = 0.034). The ratio of the levofloxacin concentration in CSF to the concentration in plasma progressively increased with time, from 0.30 immediately after dosing to 0.99 at the end of the dosing interval. In the ventricular CSF of patients with uninflamed meninges, levofloxacin was shown to provide optimal exposure, which approximately corresponded to the level of exposure of the unbound drug in plasma. The findings provide support for trials of levofloxacin with twice-daily dosing in combination with a reference beta-lactam for the treatment of bacterial meningitis in adults. This cotreatment could be useful both for overcoming Streptococcus pneumoniae resistance and for enabling optimal exposure of the CSF to at least one antibacterial agent for the overall treatment period.