Impact of the dosage schedule on the efficacy of ceftazidime, gentamicin and ciprofloxacin in Klebsiella pneumoniae pneumonia and septicemia in leukopenic rats

Challenges for global antibiotic regimen planning and establishing antimicrobial resistance targets: implications for the WHO Essential Medicines List and AWaRe antibiotic book dosing

SUMMARYThe World Health Organisation's 2022 AWaRe Book provides guidance for the use of 39 antibiotics to treat 35 infections in primary healthcare and hospital facilities. We review the evidence underpinning suggested dosing regimens. Few (n = 18) population pharmacokinetic studies exist for key oral AWaRe antibiotics, largely conducted in homogenous and unrepresentative populations hindering robust estimates of drug exposures. Databases of minimum inhibitory concentration distributions are limited, especially for community pathogen-antibiotic combinations. Minimum inhibitory concentration data sources are not routinely reported and lack regional diversity and community representation. Of studies defining a pharmacodynamic target for ß-lactams (n = 80), 42 (52.5%) differed from traditionally accepted 30%-50% time above minimum inhibitory concentration targets. Heterogeneity in model systems and pharmacodynamic endpoints is common, and models generally use intravenous ß-lactams. One-size-fits-all pharmacodynamic targets are used for regimen planning despite complexity in drug-pathogen-disease combinations. We present solutions to enable the development of global evidence-based antibiotic dosing guidance that provides adequate treatment in the context of the increasing prevalence of antimicrobial resistance and, moreover, minimizes the emergence of resistance.

Impact of therapeutic drug monitoring of antibiotics in the management of infective endocarditis

Treatment of infective endocarditis (IE) is based on high doses of antibiotics with a prolonged duration. Therapeutic drug monitoring (TDM) allows antibiotic prescription optimization and leads to a personalized medicine, but no study evaluates its interest in the management of IE. We conducted a retrospective, bicentric, descriptive study, from January 2007 to December 2019. We included patients cared for IE, defined according to Duke's criteria, for whom a TDM was requested. Clinical and microbiological data were collected after patients' charts review. We considered a trough or steady-state concentration target of 20 to 50 mg/L. We included 322 IE episodes, corresponding to 306 patients, with 78.6% (253/326) were considered definite according to Duke's criteria. Native valves were involved in 60.5% (185/306) with aortic valve in 46.6% (150/322) and mitral in 36.3% (117/322). Echocardiography was positive in 76.7% (247/322) of cases. After TDM, a dosage modification was performed in 51.5% (166/322) (decrease in 84.3% (140/166)). After initial dosage, 46.3% (82/177) and 92.8% (52/56) were considered overdosed, when amoxicillin and cloxacillin were used, respectively. The length of hospital stay was higher for patient overdosed (25 days versus 20 days (p = 0.04)), and altered creatinine clearance was associated with overdosage (p = 0.01). Our study suggests that the use of current guidelines probably leads to unnecessarily high concentrations in most patients. TDM benefits predominate in patients with altered renal function, but probably limit adverse effects related to overdosing in most patients.

How to optimize administration of cefoxitin for the treatment of extended spectrum producing Enterobacteriaceae-related infection?

Pharmacological and clinical data regarding cefoxitin for the treatment of ESBL-producing Enterobacteriaceae-related infections are limited. We performed a multicentric prospective cohort study to evaluate continuous/prolonged, or intermittent infusion of cefoxitin. We assessed the plasma concentration as a function of the duration of infusion and then performed a simulation of the percentage of patients who would reach the PK/PD targets, set at 100% ƒT_{> MIC} or 100% ƒT_{>4 MIC}. Eighty-one patients were included. All patients were treated with 6 gr./day. MICs to cefoxitin ranged from 0.5 to 64 mg/L. Sixteen (19.7%) patients were infected with strains with cefoxitin MICs ≥ 8 mg/L. In all patients infected with strains with MICs ≤ 6 mg/L, PK/PD objectives (100% ƒT_{> MIC}) were achieved with prolonged or continuous infusion. In contrast, when MICs were 8 mg/L only, continuous infusion was sufficient to achieve the PK/PD objectives (100% ƒT_{> MIC}). Extended infusion of cefoxitin is necessary for the treatment of non-UTI ESBL-related infections.

[Pharmacokinetic modifications and pharmacokinetic/pharmacodynamic optimization of beta-lactams in ICU]

Pharmacokinetic modifications in critically ill patients and those induced by ICU therapeutics raise a lot of issues about antibiotic dose adaptation. Beta-lactams are anti-infectious widely used in ICU. Frequent beta-lactam underdoses induce a risk of therapeutic failure potentially lethal and of emergence of bacterial resistance. Overdoses expose to a neurotoxic and nephrotoxic risk. Therefore, an understanding of pharmacokinetics modifications appears to be essential. A global pharmacokinetic/pharmacodynamic approach is required, including use of prolonged or continued beta-lactam infusions to optimise probability of pharmacokinetic/pharmacodynamic target attainment. Beta-lactam therapeutic drug monitoring should also be considered. Experts agree to target a free plasma betalactam concentration above four times the MIC of the causative bacteria for 100 % of the dosing interval. Bayesian methods could permit individualized doses adaptations.

Personalized antibiotic therapy – a rapid high performance liquid chromatography–tandem mass spectrometry method for the quantitation of eight antibiotics and voriconazole for patients in the intensive care unit

Objectives

For a long time, the therapeutic drug monitoring of anti-infectives (ATDM) was recommended only to avoid the toxic side effects of overdosing. During the last decade, however, this attitude has undergone a significant change. Insufficient antibiotic therapy may promote the occurrence of drug resistance; therefore, the “one-dose-fits-all” principle can no longer be classified as up to date. Patients in intensive care units (ICU), in particular, can benefit from individualized antibiotic therapies.

Methods

Presented here is a rapid and sufficient LC-MS/MS based assay for the analysis of eight antibiotics (ampicillin, cefepime, cefotaxime, ceftazidime, cefuroxime, linezolid, meropenem, and piperacillin) applicated by continuous infusion and voriconazole. In addition a dose adjustment procedure for individualized antibiotic therapy has been established.

Results

The suggested dose adjustments following the initial dosing of 121 patient samples from ICUs, were evaluated over a period of three months. Only a minor percentage of the serum levels were found to be within the target range while overdosing was often observed for β-lactam antibiotics, and linezolid tended to be often underused. The results demonstrate an appreciable potential for β-lactam savings while enabling optimal therapy.

Conclusions

The presented monitoring method provides high specificity and is very robust against various interferences. A fast and straightforward method, the developed routine ensures rapid turnaround time. Its application has been well received by participating ICUs and has led to an expanding number of hospital wards participating in ATDM.

Animal models in the pharmacokinetic/pharmacodynamic evaluation of antimicrobial agents

Animal infection models in the pharmacokinetic/pharmacodynamic (PK/PD) evaluation of antimicrobial therapy serve an important role in preclinical assessments of new antibiotics, dosing optimization for those that are clinically approved, and setting or confirming susceptibility breakpoints. The goal of animal model studies is to mimic the infectious diseases seen in humans to allow for robust PK/PD studies to find the optimal drug exposures that lead to therapeutic success. The PK/PD index and target drug exposures obtained in validated animal infection models are critical components in optimizing dosing regimen design in order to maximize efficacy while minimize the cost and duration of clinical trials. This review outlines the key components in animal infection models which have been used extensively in antibiotic discovery and development including PK/PD analyses.

Pharmacodynamic Properties of Antibiotics: Application to Drug Monitoring and Dosage Regimen Design

The goal of antimicrobial chemotherapy is to effectively eradicate pathogenic organisms while minimizing the likelihood of drug-related adverse effects. In this era of cost containment, consideration should also be given to performing this task with the smallest total dose of drug and the shortest duration of therapy. Determination of the appropriate dose and dosing interval of an antimicrobial requires knowledge and integration of both its pharmacokinetic and pharmacodynamic properties.

How severe is antibiotic pharmacokinetic variability in critically ill patients and what can be done about it?

The pharmacokinetics (PK) of antimicrobial agents administered to critically ill patients exhibit marked variability. This variability results from pathophysiological changes that occur in critically ill patients. Changes in volume of distribution, clearance, and tissue penetration all affect the drug concentrations at the site of infection. PK-pharmacodynamic indices (fCmax:MIC; AUC0-24:MIC; fT>MIC; fCmin:MIC) for both antimicrobial effect and suppression of emergence of resistance are described for many antimicrobial drugs. Changing the regimen by which antimicrobial drugs are delivered can help overcome the PK variability and optimise target attainment. This will deliver optimised antimicrobial chemotherapy to individual critically ill patients. Delivery of β-lactams antimicrobial agents by infusions, rather than bolus dosing, is effective at increasing the duration of the dosing interval that the drug concentration is above the MIC. Therapeutic drug monitoring, utilising population PK mathematical models with Bayesian estimation, can also be used to optimise regimens following measurement of plasma drug concentrations. Clinical trials are required to establish if patient outcomes can be improved by implementing these techniques.

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 infusion of antibiotics in the critically ill: The new holy grail for beta-lactams and vancomycin?

The alarming global rise of antimicrobial resistance combined with the lack of new antimicrobial agents has led to a renewed interest in optimization of our current antibiotics. Continuous infusion (CI) of time-dependent antibiotics has certain theoretical advantages toward efficacy based on pharmacokinetic/pharmacodynamic principles. We reviewed the available clinical studies concerning continuous infusion of beta-lactam antibiotics and vancomycin in critically ill patients. We conclude that CI of beta-lactam antibiotics is not necessarily more advantageous for all patients. Continuous infusion is only likely to have clinical benefits in subpopulations of patients where intermittent infusion is unable to achieve an adequate time above the minimal inhibitory concentration (T > MIC). For example, in patients with infections caused by organisms with elevated MICs, patients with altered pharmacokinetics (such as the critically ill) and possibly also immunocompromised patients. For vancomycin CI can be chosen, not always for better clinical efficacy, but because it is practical, cheaper, associated with less AUC_24h (area under the curve >24 h)-variability, and easier to monitor.

Therapeutic drug monitoring of antimicrobials

Optimizing the prescription of antimicrobials is required to improve clinical outcome from infections and to reduce the development of antimicrobial resistance. One such method to improve antimicrobial dosing in individual patients is through application of therapeutic drug monitoring (TDM). The aim of this manuscript is to review the place of TDM in the dosing of antimicrobial agents, specifically the importance of pharmacokinetics (PK) and pharmacodynamics (PD) to define the antimicrobial exposures necessary for maximizing killing or inhibition of bacterial growth. In this context, there are robust data for some antimicrobials, including the ratio of a PK parameter (e.g. peak concentration) to the minimal inhibitory concentration of the bacteria associated with maximal antimicrobial effect. Blood sampling of an individual patient can then further define the relevant PK parameter value in that patient and, if necessary, antimicrobial dosing can be adjusted to enable achievement of the target PK/PD ratio. To date, the clinical outcome benefits of a systematic TDM programme for antimicrobials have only been demonstrated for aminoglycosides, although the decreasing susceptibility of bacteria to available antimicrobials and the increasing costs of pharmaceuticals, as well as emerging data on pharmacokinetic variability, suggest that benefits are likely.

Therapeutic drug monitoring of beta-lactams in critically ill patients: proof of concept

The extreme pharmacokinetic behaviour of drugs sometimes observed in critically ill patients poses a significant threat to the achievement of optimal antibiotic treatment outcomes. Scant information on beta-lactam antibiotic therapeutic drug monitoring (TDM) is available. The objective of this prospective study was to evaluate the practicality and utility of a beta-lactam TDM programme in critically ill patients. TDM was performed twice weekly on all eligible patients at a 30-bed tertiary referral critical care unit. Blood concentrations were determined by fast-throughput high-performance liquid chromatography (HPLC) assays and were available within 12h of sampling. Dose adjustment was instituted if the trough or steady-state blood concentration was below 4-5x the minimum inhibitory concentration (MIC) or above 10x MIC. A total of 236 patients were subject to TDM over an 11-month period. The mean+/-standard deviation age was 53.5+/-18.3 years. Dose adjustment was required in 175 (74.2%) of the patients, with 119 of these patients (50.4%) requiring dose increases after the first TDM. For outcome of therapy, 206 (87.3%) courses resulted in a positive treatment outcome and there were 30 (12.7%) treatment failures observed including 14 deaths and 15 courses requiring escalation to broader-spectrum agents; 1 course was ceased due to an adverse drug reaction. Using binomial logistic regression, only an elevated Acute Physiology and Chronic Health Evaluation (APACHE) II score (P<0.01) and elevated plasma creatinine concentration (P=0.05) were found to be predictive of mortality. In conclusion, further research is required to determine definitively whether achievement of optimal beta-lactam pharmacodynamic targets improves clinical outcomes.

Pharmacokinetic and pharmacodynamic parameters of antimicrobials: potential for providing dosing regimens that are less vulnerable to resistance

Whereas infections caused by multidrug-resistant micro-organisms are increasing worldwide, there are few new molecules, especially ones that are active against Gram-negative strains. There are extensive data showing that the administration of antimicrobials according to pharmacokinetic/pharmacodynamic parameters improves the possibility of a positive clinical outcome, particularly in severely ill patients. Evidence is growing that when pharmacokinetic/pharmacodynamic parameters are used to target not only clinical cure but also eradication, the spread of resistance will also be contained. The present paper summarizes the most relevant papers published in this field and provides some suggestions for dosing regimens that can be adopted in the clinical setting to limit the spread of resistance.

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.

Antibiotic resistance--what's dosing got to do with it?

OBJECTIVE

This review seeks to identify original research articles that link antibiotic dosing and the development of antibiotic resistance for different antibiotic classes. Using this data, we seek to apply pharmacodynamic principles to assist clinical practice for suppressing the emergence of resistance. Concepts such as mutant selection window and mutant prevention concentration will be discussed.

DATA SOURCES

PubMed, EMBASE, and the Cochrane Controlled Trial Register.

STUDY SELECTION

All articles that related antibiotic doses and exposure to the formation of antibiotic resistance were reviewed.

DATA SYNTHESIS

The escalation of antibiotic resistance continues worldwide, most prominently in patients in intensive care units. Data are emerging from in vitro and in vivo studies that suggest that inappropriately low antibiotic dosing may be contributing to the increasing rate of antibiotic resistance. Fluoroquinolones have widely been researched and publications on other antibiotic classes are emerging. Developing dosing regimens that adhere to pharmacodynamic principles and maximize antibiotic exposure is essential to reduce the increasing rate of antibiotic resistance.

CONCLUSIONS

Antibiotic dosing must aim to address not only the bacteria isolated, but also the most resistant subpopulation in the colony, to prevent the advent of further resistant infections because of the inadvertent selection pressure of current dosing regimens. This may be achieved by maximizing antibiotic exposure by administering the highest recommended dose to the patient.

Continuous infusion of beta-lactams

PURPOSE OF REVIEW

Continuous infusion of beta-lactam antibiotics is becoming increasingly popular. The background and current clinical evidence are discussed. Tools to apply continuous infusion are analyzed.

RECENT FINDINGS

One randomized controlled trial in an ICU setting and two nonrandomized controlled trials have shown continuous infusion to be more beneficial than intermittent infusion. One randomized controlled trial in chronic obstructive pulmonary disorder patients, however, showed no difference between the two treatments. The stability of most beta-lactams for use during continuous infusion has been documented.

SUMMARY

Killing of bacteria by beta-lactam antibiotics is maximal at around four times the minimum inhibitory concentration in vitro. To ensure an optimal effect when treating severe infections, free unbound concentrations at or above four times the minimum inhibitory concentration should be maintained. Although continuous infusion has been demonstrated to be superior in animal studies, randomized clinical trials have failed to confirm this in humans, primarily because of suboptimal design. A better designed randomized clinical trial, set up as a pilot study, recently demonstrated a favorable outcome with continuous infusion. A major issue during continuous infusion is the stability of the antibiotic, which may limit its application. The calculation of the infusion rate necessary to obtain the desired free drug concentration is relatively straightforward.

Lung deposition of continuous and intermittent intravenous ceftazidime in experimental Pseudomonas aeruginosa bronchopneumonia

OBJECTIVE

Lung tissue deposition of intravenous ceftazidime administered either continuously or intermittently was compared in ventilated piglets with experimental bronchopneumonia.

DESIGN

Prospective experimental study

ANIMALS

Eighteen anesthetized and ventilated piglets

INTERVENTIONS

Bronchopneumonia was produced by the intrabronchial inoculation of Pseudomonas aeruginosa characterized by an impaired sensitivity to ceftazidime (MIC 16 mg/l). Ceftazidime was administered either through a continuous infusion of 90 mg/kg per 24 h after a bolus of 30 mg/kg or by an intermittent infusion of 30 mg/kg per 8 h.

MEASUREMENTS AND RESULTS

Piglets were killed 24 h after the initiation of continuous ceftazidime (n = 6), and 1 h (peak, n = 6) and 8 h (trough, n = 6) after the third dose following intermittent administration. Lung tissue concentrations of ceftazidime, measured by HPLC, and lung bacterial burden were assessed on multiple postmortem lung specimens. During continuous administration ceftazidime lung tissue concentrations were 9.7 +/- 3.8 microg/g. Following intermittent administration peak and trough lung tissue concentrations were, respectively, 7.1 +/- 2.4 microg/g and 0.6 +/- 1 microg/g. Lung bacterial burden was different after continuous and intermittent administration (median 7.10(3) vs. 4.10(2) cfu/g).

CONCLUSIONS

Continuous infusion of ceftazidime maintained higher tissue concentrations than intermittent administration.

Antibacterial Dosing in Intensive Care

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 V(d) 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 V(d) 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.

Influence of renal replacement therapy on pharmacokinetics in critically ill patients

Critical illness has a great impact on many pharmacokinetic parameters. An increased volume of distribution often results in drug underdosing, whereas organ impairment may lead to drug accumulation and overdosing. Renal replacement therapy (RRT) in critically ill patients with renal failure may significantly increase drug clearance, requiring drug-dosing adjustments. Drugs significantly eliminated by the kidney are likely to experience substantial removal during RRT, and a supplemental dose--corresponding to the amount of drug removed by RRT--should be administered. Mechanisms of drug removal during RRT are reviewed together with methods for measuring or estimating RRT drug clearances. Approaches for drug-dosing adjustments are suggested and, at the end, the pharmacological principles for antibiotic prescription in the critically ill are discussed.

Experimental models of pulmonary infection

Experimental models of pulmonary infection are being discussed, focused on various aspects of good experimental design, such as choice of animal species and infecting strain, and route of infection/inoculation techniques (intranasal inoculation, aerosol inoculation, and direct instillation into the lower respiratory tract). In addition, parameters to monitor pulmonary infection are being reviewed such as general clinical signs, pulmonary-associated signs, complication of the pulmonary infection, mortality rate, and parameters after dissection of animals. Examples of pulmonary infection models caused by bacteria, fungi, viruses or parasites in experimental animals with intact or impaired host defense mechanisms are shortly summarized including key-references.

Pharmacological principles of antibiotic prescription in the critically ill

The goal of antimicrobial prescription is to achieve effective drug concentrations. Standard antimicrobial dosing regimens are based on research performed often decades ago and for the most part with patients who were not critically ill. More recent insights into antibiotic activity (e.g. the importance of high peak/MIC ratios for aminoglycosides and time above MIC for beta-lactam antibiotics), drug pharmacokinetics (e.g. increased volume of distribution and altered clearances) and the pathogenesis of sepsis (e.g. third space losses and altered creatinine clearances) have made re-evaluation of dosing regimens necessary for the critically ill. The inflammatory response associated with sepsis results in a rapid decrease in serum albumin levels, large fluid shifts and third space losses, initially with a high cardiac output. In turn these changes result in increased creatinine clearance and increased renal drug clearance. Unless these effects are offset by ensuing renal and/or hepatic impairment, with subsequent drug accumulation, antibiotic levels may be too low for optimal efficacy. The institution of continuous renal replacement therapy separately affects antibiotic clearances, and therefore dosing, even further. This article reviews relevant literature and offers principles for more effective and appropriate antibiotic dosing in the critically ill, based on the pharmacokinetic and pharmacodynamic principles of the main antibiotic groups (aminoglyosides, glycopeptides, beta-lactams, carbapenems and quinolones) and knowledge of the pathophysiology of the inflammatory response syndrome. Finally it also provides some guidance on the basic principles of drug prescription for patients receiving continuous renal replacement therapy.

Antibiotic efficacy in vivo predicted by in vitro activity

A brief overview of arguments found in the literature is presented to apply the E(max) concept to experimental studies of antibiotics as well as to their clinical application. It may turn out to be more flexible than schedules based on arbitrary parameters that have the disadvantage that they have to be proven in each individual situation.

Comparison of in-vitro pharmacodynamics of once and twice daily ciprofloxacin

The pharmacodynamics of ciprofloxacin were explored in an in-vitro continuous bacterial culture model of infection, by simulating two oral dosing regimens; 0.5 g 12-hourly (bd) and 1 g 24-hourly (od). Three strains of Escherichia coli (ciprofloxacin MICs 0.03, 0.5 and 2 mg/L); two strains of Pseudomonas aeruginosa (MICs 0.09 and 1.5 mg/L), two strains of Staphylococcus aureus (MICs 0.12 and 1 mg/L) and two strains of Streptococcus pneumoniae (MICs 0.5 and 2 mg/L) were used. Three pharmacodynamic parameters, T > MIC, C(max)/MIC and AUC/MIC (T = time, C(max) = peak serum concentration, AUC = area under the curve), were compared with area under the bacterial-kill curve (AUBKC) (after transformation of the AUBKC) using a simple E(max) or sigmoidal E(max) model. AUBKC was taken to be the main antibacterial effect measure. The models were compared by inspection of residuals and Akaike information criterion. E(max) models adequately described the relationship between AUC/MIC and AUBKC and between C(max)/MIC and AUBKC, but not between T> MIC and AUBKC. All three pharmacodynamic parameters are related to each other but multiple regression analysis indicated that AUC/MIC was the best individual predictor of AUBKC. Despite this, comparison of od and bd regimens indicates some advantage to od in terms of early antibacterial effect. Serum concentration-time curve shape has some importance in determining antibacterial effect. These data indicate that for ciprofloxacin AUC/MIC ratio is not the sole determinant of antibacterial effect.

Use of pharmacodynamic indices to predict efficacy of combination therapy in vivo

Although combination therapy with antimicrobial agents is often used, no available method explains or predicts the efficacies of these combinations satisfactorily. Since the efficacies of antimicrobial agents can be described by pharmacodynamic indices (PDIs), such as area under the concentration-time curve (AUC), peak level, and the time that the concentration is above the MIC (time>MIC), it was hypothesized that the same PDIs would be valid in explaining efficacy during combination therapy. Twenty-four-hour efficacy data (numbers of CFU) for Pseudomonas aeruginosa in a neutropenic mouse thigh model were determined for various combination regimens: ticarcillin-tobramycin (n = 41 different regimens), ceftazidime-netilmicin (n = 60), ciprofloxacin-ceftazidime (n = 59), netilmicin-ciprofloxacin (n = 38) and for each of these agents given singly. Multiple regression analysis was used to determine the importance of various PDIs (time>MIC, time>0.25 x the MIC, time>4 x the MIC, peak level, AUC, AUC/MIC, and their logarithmically transformed values) during monotherapy and combination therapy. The PDIs that best explained the efficacies of single-agent regimens were time>0.25 x the MIC for beta-lactams and log AUC/MIC for ciprofloxacin and the aminoglycosides. For the combination regimens, regression analysis showed that efficacy could best be explained by the combination of the two PDIs that each best explained the response for the respective agents given singly. A regression model for the efficacy of combination therapy was developed by use of a linear combination of the regression models of the PDI with the highest R(2) for each agent given singly. The model values for the single-agent therapies were then used in that equation, and the predicted values that were obtained were compared with the experimental values. The responses of the combination regimens could best be predicted by the sum of the responses of the single-agent regimens as functions of their respective PDIs (e.g., time>0.25 x the MIC for ticarcillin and log AUC/MIC for tobramycin). The relationship between the predicted response and the observed response for the combination regimens may be useful for determination of the presence of synergism. We conclude that the PDIs for the individual drugs used in this study are class dependent and predictive of outcome not only when the drugs are given as single agents but also when they are given in combination. When given in combination, there appears to be a degree of synergism independent of the dosing regimen applied.

Pharmacokinetic profiles of high-dose intravenous ciprofloxacin in severe sepsis. The Baragwanath Ciprofloxacin Study Group

The pharmacokinetics of 400 mg of ciprofloxacin given intravenously (i.v.) every 8 h (q8h) in severely septic adults was documented in a multidisciplinary, tertiary referral intensive care unit (ICU). Sixteen evaluable patients (three pharmacokinetic profiles) without renal dysfunction and with severe sepsis were studied. Ciprofloxacin at a dosage of 400 mg given i.v. q8h was administered over 1 h. Plasma samples for assay (high-pressure liquid chromatography) were taken at timed intervals (preinfusion, at the end of infusion, and at 1, 2, 3, 5, and 7 h postinfusion) for first-dose kinetics (day 0 [D0]), D2, and between D6 and D8. All pharmacokinetic variables were calculated by noncompartmental methods. Standard intensive care was provided. Peak ciprofloxacin concentrations were as follows: D0, 6. 01 +/- 1.93 mg/liter; D2, 6.68 +/- 2.01 mg/liter; and D6 to D8 6.45 +/- 1.54 mg/liter. Trough levels were as follows: D0, 0.6 +/- 0.5 mg/liter; D2, 0.7 +/- 0.4 mg/liter; and D6 to D8 0.6 +/- 0.4 mg/liter. The areas under the concentration curves (8 h) were as follows: D0, 13.3 +/- 3.8 mg . h/liter; D2, 16.8 +/- 5.4 mg . h/liter; and D6 to D8, 15.5 +/- 4.7 mg . h/liter. No drug-related serious adverse events occurred. For 17 of 18 patients enrolled in the study, the causative organisms were susceptible to ciprofloxacin. One patient developed renal failure (non-drug related) after the administration of three doses of ciprofloxacin. One patient was infected with ciprofloxacin-resistant organisms on enrollment. Nine of 16 evaluable patients had clinical cures, and 8 had bacteriological cures. One patient developed a ciprofloxacin-resistant superinfection. In two patients the clinical course was indeterminate. Two bacteriological failures occurred. We conclude that in critically ill adults ciprofloxacin at a dosage of 400 mg given i.v. q8h is safe. Its pharmacokinetic profile provides bactericidal activity against most organisms encountered in an ICU. Except for some initial accumulation on D2, no further accumulation occurred in patients without renal failure. Ciprofloxacin should be administered i.v. at a dosage of 400 mg q8h for severe sepsis.

Sequential antimicrobial therapy: pharmacokinetic and pharmacodynamic considerations in sequential therapy

The pharmacodynamic factors important in sequential therapy are largely unknown. This is because most pharmacodynamic investigations concentrate on how bacterial populations respond to first antimicrobial exposures. However, it is likely that for B lactams T>MIC and for quinolones the antimicrobial AUC/MIC ratio will be important. Factors which reduce antimicrobial absorption will impact on these parameters and require further study.

Bactericidal effects of levofloxacin in comparison with those of ciprofloxacin and sparfloxacin

OBJECTIVE: To investigate and compare the in vitro activity of levofloxacin with the activities of ciprofloxacin and sparfloxacin. METHODS: The following experiments were performed: (1) comparative studies of the rate of killing by the three quinolones of different strains of Streptococcus pneumoniae at a concentration corresponding to the 1-h serum level following a 500-mg dose in humans; (2) comparative studies of the rate of killing by levofloxacin and ciprofloxacin of different strains of Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa at the same concentrations as above; (3) comparative studies of the rate of killing by levofloxacin at four different concentrations of reference and clinical strains of Streptococcus pneumoniae, Staphylococcus aureus, E. coli and P. aeruginosa. RESULTS: Levofloxacin exhibited statistically significantly higher bactericidal activity than sparfloxacin after 2 and/or 3 h against all strains of Streptococcus pneumoniae. Compared to ciprofloxacin, levofloxacin showed a statistically significantly higher bactericidal activity after 2 and/or 3 h against all strains of Streptococcus pneumoniae except the one resistant to both penicillin and cefotaxime. No differences in killing rate between levofloxacin and ciprofloxacin were seen against Staphylococcus aureus, E. coli and P. aeruginosa, with almost complete killing after 3 h of the P. aeruginosa strains and after 6 h for the E. coli strains. No concentration-dependent killing was seen at concentrations above 4xMIC of levofloxacin against Staphyloccus aureus, E. coli and P. aeruginosa. CONCLUSION: Levofloxacin was shown to be active against both Gram-positive and Gram-negative bacteria. In terms of MIC values, ciprofloxacin was the most active drug against the Gram-negative organisms, and sparfloxacin against the strains of Streptococcus pneumoniae, but levofloxacin exhibited a similar or even better bactericidal activity against the investigated strains compared with the other two fluoroquinolones when killing curves were compared.

Continuous antibiotic treatment for experimental abdominal sepsis: effects on organ inflammatory cytokine expression and neutrophil sequestration

BACKGROUND

Tumour necrosis factor (TNF) alpha and interleukin (IL) 1 beta are produced in the lung after peritonitis and may contribute to neutrophil-mediated organ injury. It was hypothesized that, during experimental peritonitis, continuous rather than intermittent antibiotic therapy would reduce lung expression of TNF-alpha and IL-1 beta messenger RNA (mRNA) and neutrophil sequestration.

METHODS

After caecal ligation and puncture, mice received either intermittent or continuous cefoxitin, or continuous metronidazole or aztreonam. Cytokine mRNAs were determined by reverse transcription differential polymerase chain reaction and lung neutrophil content by myeloperoxidase (MPO) assay.

RESULTS

Continuous cefoxitin reduced median (interquartile range (i.q.r.)) lung IL-1 beta mRNA expression ((ratio to beta-actin): continuous 0.18 (0.14-0.34), intermittent 0.46 (0.44-0.49), saline 0.43 (0.38-0.53), P < 0.05) and median (i.q.r.) lung MPO content (continuous 22.5 (9.7-40), intermittent 65 (57.5-76), saline 47 (41-64), P < 0.05) compared with intermittent therapy and saline controls. Continuous infusion was also associated with reduced bacteraemia (P < 0.05) but not serum TNF-alpha or endotoxin levels. Both continuous metronidazole and aztreonam reduced lung MPO concentration (P < 0.05) and TNF-alpha and IL-1 beta mRNA expression (P < 0.05) compared with those in saline controls. These effects were dependent on a reduction in the number of susceptible bacteria rather than serum TNF-alpha or endotoxin levels.

CONCLUSION

The stimulus for organ inflammatory cytokine production and neutrophil sequestration during peritonitis is the level of bacteraemia present, which is more effectively controlled with continuous antibiotic therapy.

Single or multiple daily doses of aminoglycosides: a meta-analysis

OBJECTIVE

To assess relative efficacy and toxicity of aminoglycosides given by single daily dose compared with multiple daily doses.

DESIGN

Meta-analysis of 21 randomised trials identified through MEDLARS (1966 to January 1995). Data were overviewed with fixed effects and random effects models and with meta-regression analysis.

SUBJECTS

Total of 3091 patients with bacterial infection, most without pre-existing renal disease.

INTERVENTIONS

Patients were randomized to receive aminoglycosides once daily or multiple times daily with similar total daily dose.

MAIN OUTCOME MEASURES

Clinical failure of treatment, nephrotoxicity, ototoxicity, and mortality.

RESULTS

Single daily dose regimen produced a non-significant decrease in risk of antibiotic failures (random effects risk ratio 0.83 (95% confidence interval 0.57 to 1.21)). Benefit of once daily dosing was greater when the percentage of pseudomonas isolates in a trial was larger. Once daily administration reduced risk of nephrotoxicity (fixed effects risk ratio 0.74 (0.54 to 1.00)). Similar trends were noted for patients with febrile neutropenia and for children. There was no significant difference in ototoxicity between the two dosing regimens, but the power of the pooled trials to detect a meaningful difference was low. There was no significant difference in mortality.

CONCLUSIONS

Once daily administration of aminoglycosides in patients without pre-existing renal impairment is as effective as multiple daily dosing, has a lower risk of nephrotoxicity, and no greater risk of ototoxicity. Given the additional convenience and reduced cost, once daily dosing should be the preferred mode of administration.

Pharmacokinetic contributions to postantibiotic effects. Focus on aminoglycosides

The postantibiotic effect (PAE) refers to a period of time after complete removal of an antimicrobial during which there is no growth of the target organism. The PAE appears to be a feature of most antimicrobial agents and has been documented with a variety of common bacterial pathogens. Various factors influence the presence or duration of the PAE including the type of organism, type of antimicrobial, concentration of antimicrobial, duration of antimicrobial exposure, antimicrobial combinations, and inoculum and medium used. beta-Lactams demonstrate a PAE against Gram-positive cocci, but produce only a short PAE with Gram-negative bacilli. Antimicrobial agents that inhibit RNA or protein synthesis have a PAE against Gram-positive cocci and Gram-negative bacilli. In vivo studies of aminoglycosides suggest that area under the plasma concentration-time curve is the pharmacokinetic parameter that best correlates with clinical efficacy. This is thought to be due to the concentration-dependent killing and PAE possessed by these antimicrobials. Animal and human studies have reported that once-daily administration of aminoglycoside is as effective as, or more effective than, and possibly less toxic than traditional multiple daily administration.

Pharmacodynamics of antimicrobial agents as a basis for determining dosage regimens

Pharmacodynamic parameters, such as the rate of bactericidal activity with increasing drug concentrations, post-antibiotic effect, sub-MIC effects, post-antibiotic leukocyte enhancement and first-exposure effect, more accurately describe the time course of antimicrobial activity than the MIC and MBC. Aminoglycosides and quinolones exhibit concentration-dependent killing and induce prolonged post-antibiotic effects. The amount of drug rather than the dosing frequency determines the efficacy of these drugs. However, high peak levels can reduce the emergence of resistance, and once-daily dosing of aminoglycosides can also reduce nephrotoxicity and ototoxicity. On the other hand, beta-lactam antibiotics show time-dependent killing and produce prolonged post-antibiotic effects only with staphylococci. The frequency of drug administration is an important determinant of outcome for these drugs, as the duration of time serum levels exceed the MIC is the major determinant of efficacy.

Impact of the duration of infection on the activity of ceftazidime, gentamicin and ciprofloxacin in Klebsiella pneumoniae pneumonia and septicemia in leukopenic rats

An experimental Klebsiella pneumoniae pneumonia and septicemia in leukopenic rats was used to study the impact of the duration of infection on the bactericidal activity of ceftazidime, gentamicin and ciprofloxacin. It appeared that the number of bacteria persisting after a single intravenous injection progressively increased with delay of antibiotic administration up to 3 h after bacterial inoculation with each of the drugs tested. This effect was most pronounced for ciprofloxacin. An inoculum effect could not explain this decrease in bacterial killing. It was also observed that a single injection with a particular dose of each of the respective drugs did not kill all the Klebsiella pneumoniae organisms in the lung. Persisting bacteria did not represent a preexisting less susceptible subpopulation selected after antibiotic administration. In further experiments the impact of delay of the start of treatment on the efficacy of ceftazidime or ciprofloxacin after administration for a period of four days with intramuscular injections at 6 h intervals was investigated. Treatment was started at 5, 12 or 24 h after bacterial inoculation. The therapeutic efficacy of both drugs decreased with the increase of duration of infection, which may be at least in part due to the progressive number of bacteria persisting after antibiotic administration. These data underline the need to start antimicrobial treatment as soon as possible.

Once-daily aminoglycoside therapy

The once-daily administration of aminoglycosides is an attractive concept. In animal experiments and clinical trials, there is either a reduction in or no influence on the risk of toxicity. Less frequent dosing reduces the contact time between host tissue binding sites and drug. Thanks to the PAE and perhaps other as-yet-unrecognized factors, the fall in the level in serum below the MIC does not appear to impair antibacterial efficacy; in fact, the higher peak level in serum may enhance drug efficacy early in a dosage interval. In neutropenic patients, the in vivo PAE may be lost or small-colony variants with a shorter PAE may be selected unless a concomitant beta-lactam is administered. Because it will be some time before data from clinical trials in the United States are available, because the results from the international trials are encouraging, and because there is potential benefit to patients, it seems reasonable for infectious diseases consultants to cautiously initiate the educational process necessary to implement once-daily aminoglycoside therapy in their institutions.

Pharmacokinetics of ceftazidime in serum and suction blister fluid during continuous and intermittent infusions in healthy volunteers

The pharmacokinetics of ceftazidime were investigated during intermittent (II) and continuous (CI) infusion in eight healthy male volunteers in a crossover fashion. The total daily dose was 75 mg/kg of body weight per 24 h in both regimens, given in three doses of 25 mg/kg/8 h (II) or 60 mg/kg/24 h with 15 mg/kg as a loading dose (CI). After the third dose (II) and during CI, serum and blister fluid samples were taken. Seven new blisters were raised for each timed sample by a suction blister technique. Blisters took 90 min to form. Samples were then taken from four blisters (A samples) and 1 h later were taken from the remaining three (B samples). The concentration of ceftazidime was determined using a high-performance liquid chromatography method. After II, the concentrations in serum immediately after infusion (t = 30 min) and 8 h after the start of the infusion were 137.9 (standard deviation [SD], 27.5) and 4.0 (SD, 0.7) micrograms/ml, respectively. The half-life at alpha phase (t1/2 alpha) was 9.6 min (SD, 4.6), t1/2 beta was 94.8 min (SD, 5.4), area under the concentration-time curve (AUC) was 285.4 micrograms.h/ml (SD, 22.7), total body clearance was 0.115 liter/h.kg (SD, 0.022), and volume of distribution at steady state was 0.178 liter/kg (SD, 0.023). The blister fluid (A) samples showed a decline in concentration parallel to that of the concentrations in serum during the elimination phase with a ratio of 1:1. The t1/2 of the A samples was 96.4 min (SD, 3.2). The concentration of ceftazidime in the B blister fluid samples was significantly higher (27%) than in the A samples over time. This shows that blisters may behave as a separate compartment and establishes the need to raise new blisters for each timed sample. The mean AUC/h during continuous infusion was 21.3 micrograms . h/ml (SD, 3.0). The total body clearance was 0.113 liter/h . kg (SD, 0.018), the urinary clearance was 0.105 liter/h . kg (SD, 0.012), and the ceftazidime/creatinine clearance ratio was 0.885. The mean AUC of blister fluid per hour was 84.5% (18.0 micrograms . h/liter; SD, 3.6) compared with that of serum. The A samples did not differ significantly from the B samples. The implications of continuous infusion of beta-lactams for treatment of serious infections are discussed.

Pharmacodynamic properties of antibiotics: application to drug monitoring and dosage regimen design

The goal of antimicrobial chemotherapy is to effectively eradicate pathogenic organisms while minimizing the likelihood of drug-related adverse effects. In this era of cost containment, consideration should also be given to performing this task with the smallest total dose of drug and the shortest duration of therapy. Determination of the appropriate dose and dosing interval of an antimicrobial requires knowledge and integration of both its pharmacokinetic and pharmacodynamic properties.

Antibacterial therapy in cystic fibrosis

Bacterial lung infections determine the prognosis for most cystic fibrosis patients. The antibacterial therapy is difficult because of the host-bacterium interaction and altered pharmacokinetics. The new insights in the working mechanisms of antibiotics that may lead to better treatment results have been discussed, and guidelines for treatment of lung infections in cystic fibrosis patients were given.

Impact of dosage schedule of antibiotics on the treatment of serious infections

Experimental studies suggest that the importance of the antibiotic dosage schedule for therapeutic efficacy in severe infection and when host defences are impaired is related to the class of antibiotic. The efficacy of beta-lactams is mainly dependent on the maintenance of adequate antibiotic concentrations in plasma during the entire treatment interval, and not on high peak concentrations. The efficacy of aminoglycosides is related to the total dose administered, i.e., the area under the concentration-time curve, irrespective of the frequency of administration. This difference in efficacy between beta-lactams and aminoglycosides in relation to the dosage schedule correlate well with differences between both classes of antibiotics in kinetics of antibacterial activity in vitro and in vivo. Another factor relevant in this respect is the post-antibiotic effect (PAE) which means the suppression of bacterial regrowth at the end of the period of exposure to antibiotic.