Pharmacokinetics of intravenous and oral levofloxacin in critically ill adults in a medical intensive care unit

Ironing out Persisters? Revisiting the Iron Chelation Strategy to Target Planktonic Bacterial Persisters Harboured in Carbapenem-Resistant Escherichia coli

Antibiotic resistance is a global health crisis. Notably, carbapenem-resistant Enterobacterales (CRE) pose a significant clinical challenge due to the limited effective treatment options. This problem is exacerbated by persisters that develop upon antibiotic exposure. Bacteria persisters can tolerate high antibiotic doses and can cause recalcitrant infections, potentially developing further antibiotic resistance. Iron is a critical micronutrient for survival. We aimed to evaluate the utility of iron chelators, alone and in combination with antibiotics, in managing persisters. We hypothesized that iron chelators eradicate CRE persisters in vitro, when administered in combination with antibiotics. Our screening revealed three clinical isolates with bacteria persisters that resuscitated upon antibiotic removal. These isolates were treated with both meropenem and an iron chelator (deferoxamine mesylate, deferiprone or dexrazoxane) over 24 h. Against our hypothesis, bacteria persisters survived and resuscitated upon withdrawing both the antibiotic and iron chelator. Pursuing our aim, we next hypothesized that iron chelation is feasible as a post-antibiotic treatment in managing and suppressing persisters' resuscitation. We exposed bacteria persisters to an iron chelator without antibiotics. Flow cytometric assessments revealed that iron chelators are inconsistent in suppressing persister resuscitation. Collectively, these results suggest that the iron chelation strategy may not be useful as an antibiotic adjunct to target planktonic bacteria persisters.

Oral Antibiotics for Bacteremia and Infective Endocarditis: Current Evidence and Future Perspectives

Bacteremia and endocarditis are two clinical syndromes that, for decades, were managed exclusively with parenteral antimicrobials, irrespective of a given patient's clinical condition, causative pathogen, or its antibiotic susceptibility profile. This clinical approach, however, was based on low-quality data and outdated expert opinions. When a patient's condition has improved, gastrointestinal absorption is not compromised, and an oral antibiotic regimen reaching adequate serum concentrations is available, a switch to oral antibacterials can be applied. Although available evidence has reduced the timing of the oral switch in bacteremia to three days/until clinical improvement, there are only scarce data regarding less than 10-day intravenous antibiotic therapy in endocarditis. Many standard or studied oral antimicrobial dosages are smaller than the approved doses for parenteral administration, which is a risk factor for treatment failure; in addition, the gastrointestinal barrier may affect drug bioavailability, especially when the causative pathogen has a minimum inhibitory concentration that is close to the susceptibility breakpoint. A considerable number of patients infected by such near-breakpoint strains may not be potential candidates for oral step-down therapy to non-highly bioavailable antibiotics like beta-lactams; different breakpoints should be determined for this setting. This review will focus on summarizing findings about pathogen-specific tailoring of oral step-down therapy for bacteremia and endocarditis, but will also present laboratory and clinical data about antibiotics such as beta-lactams, linezolid, and fosfomycin that should be studied more in order to elucidate their role and optimal dosage in this context.

Pharmacoeconomic and antimicrobial stewardship analysis in waste management: Beyond switching drug administration route

BACKGROUND

The aim of this study was to evaluate the impact of switch therapy of antimicrobials on cost reduction (pharmacoeconomic analysis) and hospital waste generation by switching from intravenous to oral therapy. This is a cross-sectional, observational, and retrospective study.

METHODS

Data from 2019, 2020, and 2021, provided by the clinical pharmacy service of a teaching hospital in the interior of Rio Grande do Sul, were analyzed. The variables analyzed were intravenous and oral antimicrobials, frequency, duration of use, and total treatment time according to the institutional protocols. An estimate of the amount of waste not generated from the change of administration route was calculated by weighing the kits using a precision balance in grams.

RESULTS

During the analyzed period, 275 switch therapy of antimicrobials were performed, resulting in US$ 55,256.00 of savings. The main antimicrobial classes that underwent changes were cephalosporins (25.1%), penicillins (22.55%), and quinolones (17.45%). Changing from intravenous to oral therapy avoided the generation of 170,631 g of waste, including needles, syringes, infusion bags, equipment, reconstituted solution bottles, and medication.

CONCLUSIONS

The change from intravenous to the oral route of antimicrobials is safe for the patient, economically effective, and significantly reduces waste generation.

Bioavailability of Orally Administered Drugs in Critically Ill Patients

Critically ill patients managed in the Intensive Care Unit (ICU) suffer from several pathophysiological alterations due to critical illness resulting in potential changes in the pharmacokinetics of drugs including systemic absorption. Nevertheless, these patients are still given some medications in unadjusted doses thereby putting the patients at a risk for therapy failure. The objective for this study was to summarize the available evidence regarding oral drug absorption in the ICU. A literature search of the databases MEDLINE, EMBASE, and PubMed was conducted on (February 24, 2020). Articles discussing the rate and/or extent of orally administered drugs in critically ill patients were included. A total of 58 studies were found: 17 interventional studies, 33 observational studies (30 prospective, 3 retrospective) and 8 case reports. A total of 43 articles reported altered drug absorption in critically ill patients suggesting the need for alternative measures to facilitate treatment success. The absorption of orally administered drugs may be altered in critically ill patients. Measures for altered drug absorption in critically ill patients were suggested such as holding tube feeding before and after medication administration, increasing doses of orally administrated drugs and using alternate routes of administration.

Pharmacokinetic Drug-drug Interaction of Antibiotics Used in Sepsis Care in China

BACKGROUND

Many antibiotics have a high potential for interactions with drugs, as a perpetrator and/or victim, in critically ill patients, and particularly in sepsis patients.

METHODS

The aim of this review is to summarize the pharmacokinetic drug-drug interaction (DDI) of 45 antibiotics commonly used in sepsis care in China. Literature search was conducted to obtain human pharmacokinetics/ dispositions of the antibiotics, their interactions with drug-metabolizing enzymes or transporters, and their associated clinical drug interactions. Potential DDI is indicated by a DDI index ≥ 0.1 for inhibition or a treatedcell/ untreated-cell ratio of enzyme activity being ≥ 2 for induction.

RESULTS

The literature-mined information on human pharmacokinetics of the identified antibiotics and their potential drug interactions is summarized.

CONCLUSION

Antibiotic-perpetrated drug interactions, involving P450 enzyme inhibition, have been reported for four lipophilic antibacterials (ciprofloxacin, erythromycin, trimethoprim, and trimethoprim-sulfamethoxazole) and three antifungals (fluconazole, itraconazole, and voriconazole). In addition, seven hydrophilic antibacterials (ceftriaxone, cefamandole, piperacillin, penicillin G, amikacin, metronidazole, and linezolid) inhibit drug transporters in vitro. Despite no clinical PK drug interactions with the transporters, caution is advised in the use of these antibacterials. Eight hydrophilic antibiotics (all β-lactams; meropenem, cefotaxime, cefazolin, piperacillin, ticarcillin, penicillin G, ampicillin, and flucloxacillin), are potential victims of drug interactions due to transporter inhibition. Rifampin is reported to perpetrate drug interactions by inducing CYP3A or inhibiting OATP1B; it is also reported to be a victim of drug interactions, due to the dual inhibition of CYP3A4 and OATP1B by indinavir. In addition, three antifungals (caspofungin, itraconazole, and voriconazole) are reported to be victims of drug interactions because of P450 enzyme induction. Reports for other antibiotics acting as victims in drug interactions are scarce.

Elimination of Extracellular Adenosine Triphosphate for the Rapid Prediction of Quantitative Plate Counts in 24 h Time-Kill Studies against Carbapenem-Resistant Gram-Negative Bacteria

Traditional in vitro time-kill studies (TKSs) require viable plating, which is tedious and time-consuming. We used ATP bioluminescence, with the removal of extracellular ATP (EC-ATP), as a surrogate for viable plating in TKSs against carbapenem-resistant Gram-negative bacteria (CR-GNB). Twenty-four-hour TKSs were conducted using eight clinical CR-GNB (two Escherichia coli, two Klebsiella spp., two Acinetobacter baumannii, two Pseudomonas aeruginosa) with multiple single and two-antibiotic combinations. ATP bioluminescence and viable counts were determined at each timepoint (0, 2, 4, 8, 24 h), with and without apyrase treatment. Correlation between ATP bioluminescence and viable counts was determined for apyrase-treated and non-apyrase-treated samples. Receiver operator characteristic curves were plotted to determine the optimal luminescence threshold to discriminate between inhibitory/non-inhibitory and bactericidal/non-bactericidal combinations, compared to viable counts. After treatment of bacteria with 2 U/mL apyrase for 15 min at 37 °C, correlation to viable counts was significantly higher compared to untreated samples (p < 0.01). Predictive accuracies of ATP bioluminescence were also significantly higher for apyrase-treated samples in distinguishing inhibitory (p < 0.01) and bactericidal (p = 0.03) combinations against CR-GNB compared to untreated samples, when all species were collectively analyzed. We found that ATP bioluminescence can potentially replace viable plating in TKS. Our assay also has applications in in vitro and in vivo infection models.

Intravenous-to-oral antibiotic switch therapy: a cross-sectional study in critical care units

BACKGROUND

This study aimed to evaluate the oral switch (OS) stewardship intervention in the intensive care unit (ICU).

METHODS

This was a retrospective study with a convenience sample in two Brazilian ICUs from different hospitals in patients with sepsis receiving antibiotic therapy. The stewardship intervention included OS in patients diagnosed with sepsis when clinical stability was achieved. The primary outcome was overall mortality. Other variables evaluated were as follows: cost of antimicrobial treatment, daily costs of intensive care, acute kidney injury, and length of stay.

RESULTS

There was no difference in mortality between the OS and non-OS groups (p = 0.06). Length of stay in the ICU (p = 0.029) was shorter and acute kidney injury incidence (p = 0.032) and costs of antimicrobial therapy (p < 0.001) were lower in the OS group.

CONCLUSION

OS stewardship programs in the ICU may be considered a safe strategy. Switch therapy reduced the cost and shortened the length of stay in ICUs.

Pharmacokinetic/pharmacodynamic analysis as a tool for surveillance of the activity of antimicrobials against Pseudomonas aeruginosa strains isolated in critically ill patients

INTRODUCTION

To evaluate the changes in the susceptibility of Pseudomonas aeruginosa over time (2000-2017) against antimicrobials used in an intensive care unit of a Spanish tertiary hospital, and to compare them with the antimicrobial activity considering theoretical pharmacokinetic/pharmacodynamic (PK/PD) criteria. The influence of the method for handling duplicate isolates to quantify susceptibility rates was also evaluated.

METHODS

The susceptibility was studied considering the Clinical and Laboratory Standards Institute (CLSI) breakpoints. Monte Carlo simulations were conducted to calculate the cumulative fraction of response (CFR). Linear regression analysis was applied to determine the trends in susceptibility and in the CFR.

RESULTS

A significant decrease in the susceptibility to gentamicin and imipenem was observed, and more recently the highest percentages of susceptible strains were found for amikacin, cephalosporins and piperacillin/tazobactam (>80%). The probability of success of an empiric treatment or CFR for most of the evaluated antimicrobials was lower than 70% during the last two-year period. Only meropenem provided high probabilities (>90%) to achieve the PK/PD target. Cephalosporins provided moderate probabilities (>80%) although for ceftazidime, the highest dose (2g/8h) was required. Moreover, a significant decrease in the CFR trend for ciprofloxacin, imipenem and levofloxacin was observed.

CONCLUSIONS

Both susceptibility rates and CFR values have to be considered together to optimize the antimicrobial dose regimen for clinical making-decisions. They are complementary tools and, they should be used jointly in surveillance programmes. In fact, susceptibility data are not always useful to detect changes in the CFR. No relevant differences were observed among the methods for handling repeated isolates.

Antibiotic Stewardship Program Perspective: Oral Antibiotic Therapy for Common Infectious Diseases

Traditionally, initial antibiotic therapy was administered intravenously (IV). Over the past 3 decades, there has been increased understanding, appreciation, and application of pharmacokinetic (PK) and pharmacodynamic (PD) principles in antibiotic therapy. The utilization of PK/PD parameters as applied to antimicrobial therapy has led to optimizing dosage regimens as well as increased awareness and experience with oral versus antibiotic therapy. When an oral antibiotic, given at the same dose as its IV formulation, results in the same serum/tissue levels, then oral antibiotics should be used whenever possible. When chosen carefully, oral therapy provides many benefits over IV therapy.

Pharmacokinetic and Pharmacodynamic Considerations of Antibiotics of Last Resort in Treating Gram-Negative Infections in Adult Critically Ill Patients

PURPOSE OF REVIEW

We provide an overview of antimicrobials that are considered last resort for the treatment of resistant gram-negative infections in adult critically ill patients. The role in therapy, pharmacodynamic (PD) goals, and pharmacokinetic (PK) changes in critical illness for aminoglycosides, polymyxins, tigecycline, fosfomycin, and fluoroquinolones are summarized.

RECENT FINDINGS

Altered PK in septic patients in the intensive care unit (ICU) is observed with many of our agents of last resort. Based on the available literature, dosage adjustments may be required to optimize PK parameters and meet PD targets for most effective bacterial killing. Data is limited, studies are conducted in heterogeneous patient populations, and conclusions are frequently conflicting. Strategic dosing regimens such as high-dose extended interval dosing of aminoglycosides or loading doses with colistin and polymyxin B are examples of ways to optimize antibiotic PK in critically ill patients. Benefits of these strategies must be balanced with risks of increased toxicity. Patients with resistant gram-negative infections may present with septic shock in the ICU. Sepsis can significantly alter the PK of antibiotics and require dosage adjustments to attain optimal drug levels. An understanding of PK and PD properties of these agents of last resort will help to maximize therapeutic efficacy while minimizing toxic effects.

Humanized Exposures of Cefiderocol, a Siderophore Cephalosporin, Display Sustained in vivo Activity against Siderophore-Resistant Pseudomonas aeruginosa

We evaluated the in vivo efficacy of humanized exposures of cefiderocol, a novel siderophore cephalosporin, against a test panel of P. aeruginosa (PSA) previously shown to develop resistance to 2 preclinical candidate siderophores (MB-1 and SMC-3176). In the thigh infection model, the PSA bacterial density in untreated controls grew from 5.54 ± 0.23 to 8.68 ± 0.57 log10 CFU over 24 h. The humanized cefiderocol exposure resulted in >1 log10 CFU reduction in all 8 isolates, while MB-1 and SMC-3176 exhibited variable activity similar to that previously reported. Humanized exposures of cefepime and levofloxacin, acting as positive antimicrobial controls displayed activity consistent with that of the bacterial phenotypic susceptibility profiles. Cefiderocol manifested in vivo efficacy against all PSA isolates including those resistant to cefepime and levofloxacin in contrast to its predecessor siderophore compounds. These preclinical data are supportive of further evaluation of cefiderocol in the treatment of P. aeruginosa.

Analytical Methods for Determining Third and Fourth Generation Fluoroquinolones: A Review

ABSTRACT

Fluoroquinolones of the third and fourth generation posses wide bactericidal activity. Monitoring concentrations of antibacterial agents provides effective therapy and prevents the increase of bacterial resistance to antibiotics. The pharmacodynamic parameters that best describe fluoroquinalone activity are AUC/MIC and Cmax/MIC. Determining the level of this type of drug is essential to reach the effective concentration that inhibits the growth of bacteria. Determining the pharmaceutical formulation confirms the purity of a substance. Many methods have been developed to determine the level of these substances. They involve mainly the following analytical techniques: chromatography, capillary electrophoresis, and spectroscopy. The separation techniques were combined with different measuring devices, such as ultraviolet (UV), fluorescence detector (FLD), diode array detector (DAD), and mass spectrometry (MS). The analytical procedures require proper sample pre-conditioning such as protein precipitation, extraction techniques, filtration, or dilution. This paper reviews the reported analytical methods for the determining representatives of the third and fourth generation of fluoroquinolones. Attention was paid to pre-conditioning of the samples and the applied mobile phase. This report might be helpful in the selection of the proper procedure in determining the abovementioned drugs in different matrices.

GRAPHICAL ABSTRACT

In Vitro Activity of Polymyxin B in Combination with Various Antibiotics against Extensively Drug-Resistant Enterobacter cloacae with Decreased Susceptibility to Polymyxin B

Against extensively drug-resistant (XDR) Enterobacter cloacae, combination antibiotic therapy may be the only option. We investigated the activity of various antibiotics in combination with polymyxin B using time-kill studies (TKS). TKS were conducted with four nonclonal XDR E. cloacae isolates with 5 log10 CFU/ml bacteria against maximum, clinically achievable concentrations of polymyxin B alone and in two-drug combinations with 10 different antibiotics. A hollow-fiber infection model (HFIM) simulating clinically relevant polymyxin B and tigecycline dosing regimens was conducted for two isolates over 240 h. Emergence of resistance was quantified using antibiotic-containing (3× MIC) media. Biofitness and stability of resistant phenotypes were determined. All XDR E. cloacae isolates were resistant to all antibiotics except for polymyxin B (polymyxin B MIC, 1 to 4 mg/liter). All isolates harbored metallo-β-lactamases (two with NDM-1, two with IMP-1). In single TKS, all antibiotics alone demonstrated regrowth at 24 h, except amikacin against two strains and polymyxin B and meropenem against one strain each. In combination TKS, only polymyxin B plus tigecycline was bactericidal against all four XDR E. cloacae isolates at 24 h. In HFIM, tigecycline and polymyxin B alone did not exhibit any killing activity. Bactericidal kill was observed at 24 h for both isolates for polymyxin B plus tigecycline; killing was sustained for one isolate but regrowth was observed for the second. Phenotypically stable resistant mutants with reduced in vitro growth rates were observed. Polymyxin B plus tigecycline is a promising combination against XDR E. cloacae However, prolonged and indiscriminate use can result in resistance emergence.

From Bench-Top to Bedside: A Prospective In Vitro Antibiotic Combination Testing (iACT) Service to Guide the Selection of Rationally Optimized Antimicrobial Combinations against Extensively Drug Resistant (XDR) Gram Negative Bacteria (GNB)

Introduction

Combination therapy is increasingly utilized against extensively-drug resistant (XDR) Gram negative bacteria (GNB). However, choosing a combination can be problematic as effective combinations are often strain-specific. An in vitro antibiotic combination testing (iACT) service, aimed to guide the selection of individualized and rationally optimized combination regimens within 48 hours, was developed. We described the role and feasibility of the iACT service in guiding individualized antibiotic combination selection in patients with XDR-GNB infections.

Methods

A retrospective case review was performed in two Singapore hospitals from April 2009–June 2014. All patients with XDR-GNB and antibiotic regimen guided by iACT for clinical management were included. The feasibility and role of the prospective iACT service was evaluated. The following patient outcomes were described: (i) 30-day in-hospital all-cause and infection-related mortality, (ii) clinical response, and (iii) microbiological eradication in patients with bloodstream infections.

Results

From 2009–2014, the iACT service was requested by Infectious Disease physicians for 39 cases (20 P. aeruginosa, 13 A. baumannii and 6 K. pneumoniae). Bloodstream infection was the predominant infection (36%), followed by pneumonia (31%). All iACT recommendations were provided within 48h from request for the service. Prior to iACT-guided therapy, most cases were prescribed combination antibiotics empirically (90%). Changes in the empiric antibiotic regimens were recommended in 21 (54%) cases; in 14 (36%) cases, changes were recommended as the empiric regimens were found to be non-bactericidal in vitro. In 7 (18%) cases, the number of antibiotics used in combination empirically was reduced by the iACT service. Overall, low 30-day infection-related mortality (15%) and high clinical response (82%) were observed. Microbiological eradication was observed in 79% of all bloodstream infections.

Conclusions

The iACT service can be feasibly employed to guide the timely selection of rationally optimized combination regimens, and played a role in reducing indiscreet antibiotic use.

Pharmacokinetic Alterations of Antimicrobials in the Critically Ill

Critical illness is accompanied by multiple physiologic alterations that affect the pharmacokinetics of antimicrobials. Although the pharmacokinetics of a number of antimicrobials have been studied in critically ill individuals, an understanding of the physiological alterations in critical illness and general pharmacokinetic principles of antimicrobials is imperative for appropriate selection, dosing, and prediction of toxicity.

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.

Using an Adenosine Triphosphate Bioluminescent Assay to Determine Effective Antibiotic Combinations against Carbapenem-Resistant Gram Negative Bacteria within 24 Hours

Background

Current in vitro combination testing methods involve enumeration by bacterial plating, which is labor-intensive and time-consuming. Measurement of bioluminescence, released when bacterial adenosine triphosphate binds to firefly luciferin-luciferase, has been proposed as a surrogate for bacterial counts. We developed an ATP bioluminescent combination testing assay with a rapid turnaround time of 24h to determine effective antibiotic combinations.

Methods

100 strains of carbapenem-resistant (CR) GNB [30 Acinetobacter baumannii (AB), 30 Pseudomonas aeruginosa (PA) and 40 Klebsiella pneumoniae (KP)] were used. Bacterial suspensions (10⁵ CFU/ml) were added to 96-well plates containing clinically achievable concentrations of multiple single and two-antibiotic combinations. At 24h, the luminescence intensity of each well was measured. Receiver operator characteristic curves were plotted to determine optimal luminescence threshold (T_RLU) to discriminate between inhibitory/non-inhibitory combinations when compared to viable plating. The unweighted accuracy (UA) [(sensitivity + specificity)/2] of T_RLU values was determined. External validation was further done using 50 additional CR-GNB.

Results

Predictive accuracies of T_RLU were high for when all antibiotic combinations and species were collectively analyzed (T_RLU = 0.81, UA = 89%). When individual thresholds for each species were determined, UA remained high. Predictive accuracy was highest for KP (T_RLU = 0.81, UA = 91%), and lowest for AB (T_RLU = 0.83, UA = 87%). Upon external validation, high overall accuracy (91%) was observed. The assay distinguished inhibitory/non-inhibitory combinations with UA of 80%, 94% and 93% for AB, PA and KP respectively.

Conclusion

We developed an assay that is robust at identifying useful combinations with a rapid turn-around time of 24h, and may be employed to guide the timely selection of effective antibiotic combinations.

Addressing Concerns about Changing the Route of Antimicrobial Administration from Intravenous to Oral in Adult Inpatients

BACKGROUND

Many health care institutions are in the process of establishing antimicrobial stewardship programs. Changing the route of administration of antimicrobial agents from intravenous to oral (IV to PO) is a simple, well-recognized intervention that is often part of an antimicrobial stewardship program. However, the attending health care team may have concerns about making this switch.

OBJECTIVES

To provide insights into common concerns related to IV to PO conversion, with the aim of helping antimicrobial stewardship teams to address them.

DATA SOURCES

Published clinical trials and reviews were identified from a literature search of Ovid MEDLINE with the keywords (step down or switch or conversion or transition or sequential) and (antibiotics or antibacterial agents or antimicrobial or anti-infective agents).

DATA SYNTHESIS

The following issues are addressed in this review: benefits of the oral route, serum concentrations yielded by the oral formulation, source of pharmacokinetic data, clinical outcomes, provision of care in the intensive care unit, fear of therapeutic failure, and administration of antimicrobials via feeding tube.

CONCLUSIONS

When considering a change to oral therapy, it is important to have a thorough understanding of key aspects of the antimicrobial agent, the patient, and the disease being treated. The antimicrobial stewardship team has an important role in facilitating IV to PO conversion, educating prescribers, and addressing any concerns or reservations that may interfere with timely transition from IV to PO administration.

Haemophilus parainfluenzae aortic prosthetic valve endocarditis (PVE) successfully treated with oral levofloxacin

Antibiotic treatment of native valve infective endocarditis (IE) traditionally consists of 4-6 weeks of intravenous (IV) antibiotic therapy. Oral (PO) antibiotic therapy is being used more frequently, for part or all of treatment for IE but experience in treating IE with PO antibiotics is limited. Preferable agents for oral therapy of IE are antibiotics with a high degree of activity against the IE pathogen and that have high bioavailability (>90%) so that achievable serum and tissue levels are the same as with equivalent IV antibiotics. Oral antibiotic therapy of IE has several advantages over IV therapy given the long duration of treatment, i.e., 4-6 weeks for IE. Firstly, outpatient oral therapy for IE is easily administered over 4-6 weeks and decreases hospital length of stay (LOS). Secondly, oral antibiotics (administered at the same dose, frequency and duration) costs much less than their IV counterparts. Thirdly, with PO therapy for IE there are no central venous catheter (CVC) associated complications, e.g., phlebitis, bacteremia, fungemia. Compared to native valve IE, prosthetic valve endocarditis (PVE), depending on the IE pathogen, requires prolonged therapy and usually valve replacement. Haemophilus sp. IE is relatively virulent and often complicated by heart failure and/or embolic phenomena. We describe the first reported case of Haemophilus parainfluenzae aortic PVE successfully treated with oral levofloxacin without aortic valve replacement.

Pharmacokinetics and the optimal regimen for levofloxacin in critically ill patients receiving continuous hemodiafiltration

The aim of this study was to establish the pharmacokinetics of levofloxacin (LVFX) and determine the optimal dose of this drug in critically ill patients receiving continuous hemodiafiltration (CHDF). The results of in vivo and in vitro studies showed the pharmacokinetics of LVFX total clearance (CL_total) according to the creatinine clearance (CL_Cre), dialysate flow (Q_D), and ultrafiltrate flow (Q_F), to be as follows: CL_total (l/h) = 0.0836 × CL_Cre (ml/min) + 0.013 × body weight (kg) + 0.94(Q_D + Q_F) (l/h). The optimal dose of LVFX was expressed by the following formula: 50 × CL_total. These results demonstrate that the usual dose of LVFX (500 mg) was sufficient for the patients evaluated in this study.

In vitro pharmacodynamics of various antibiotics in combination against extensively drug-resistant Klebsiella pneumoniae

Extensively drug-resistant (XDR) Klebsiella pneumoniae is an emerging pathogen in Singapore. With limited therapeutic options available, combination antibiotics may be the only viable option. In this study, we aimed to elucidate effective antibiotic combinations against XDR K. pneumoniae isolates. Six NDM-1-producing and two OXA-181-producing K. pneumoniae strains were exposed to 12 antibiotics alone and in combination via time-kill studies. A hollow-fiber infection model (HFIM) with pharmacokinetic validation was used to simulate clinically relevant tigecycline-plus-meropenem dosing regimens against 2 XDR K. pneumoniae isolates over 240 h. The emergence of resistance against tigecycline was quantified using drug-free and selective (tigecycline at 3× the MIC) media. The in vitro growth rates were determined and serial passages on drug-free and selective media were carried out on resistant isolates obtained at 240 h. Both the polymyxin B and tigecycline MICs ranged from 1 to 4 mg/liter. In single time-kill studies, all antibiotics alone demonstrated regrowth at 24 h, except for polymyxin B against 2 isolates. Tigecycline plus meropenem was found to be bactericidal in 50% of the isolates. For the isolates that produced OXA-181-like carbapenemases, none of the 55 tested antibiotic combinations was bactericidal. Against 2 isolates in the HFIM, tigecycline plus meropenem achieved a >90% reduction in bacterial burden for 96 h before regrowth was observed until 10(9) CFU/ml at 240 h. Phenotypically stable and resistant isolates, which were recovered from tigecycline-supplemented plates post-HFIM studies, had lower growth rates than those of their respective parent isolates, possibly implying a substantial biofitness deficit in this population. We found that tigecycline plus meropenem may be a potential antibiotic combination for XDR K. pneumoniae infections, but its efficacy was strain specific.

Mutant prevention concentrations of levofloxacin, pazufloxacin and ciprofloxacin for A. baumannii and mutations in gyrA and parC genes

Fluoroquinolones are antimicrobial agents that are widely used clinically, but the increasing resistance of Acinetobacter baumannii (A. baumannii) to these agents is a matter of concern. We investigated mutant prevention concentrations (MPCs) of three fluoroquinolones, levofloxacin (LVX), pazufloxacin (PAZ) and ciprofloxacin (CIP). We analyzed an A. baumannii standard strain (ATCC19606) for mutation prevention indices (MPIs), MPCs and mutant selection windows as well as MICs of CIP, PAZ and LVX and compared the derived values with 34 A. baumannii strains collected in hospitals. In addition, A. baumannii standard strain (ATCC19606) fluoroquinolone-resistant mutants were investigated for gyrA and parC gene mutations. MPCs of CIP, prevention antibiotics concentration and LVX for A. baumannii ATCC19606 were 12.8, 5.6 and 2.8 μg ml(-1) and their MPIs were 16, 8 and 4, respectively. Clinically isolated A. baumannii strains had CIP, PAZ and LVX MPC value ranges of 1-8, 1-16 and 0.5-2 μg ml(-1) and their MPIs were 8, 8 and 4 μg ml(-1). Single gyrA mutations (Ser(83)-Leu(83)) occurred in 18 resistant strains (48.7%) and single parC mutations (Ala(79)-Asp(79) or (Ser(80)-Leu(80)) occurred in 8 resistant strains (21.6%), whereas gyrA and parC double mutations occurred in 2 (5.4%) of the resistant strains. MPC and MPI values of LVX were lower than that of CIP and PAZ. Single gyrA and parC mutations accounted for the majority of mutations (n=24), whereas double mutations occurred only in two strains.

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.

Levofloxacin: update and perspectives on one of the original ‘respiratory quinolones’

The fluoroquinolone class of antimicrobials has enjoyed enormous clinical and marketing success over the past 20 years. These drugs have proven to be extremely useful in a broad range of clinical indications including both common community-acquired as well as nosocomial bacterial infections. Levofloxacin (Levaquin, Tavanic), like ciprofloxacin (Cipro), has established an enviable record of safe and efficacious use, and in many ways has become the agent against which all of the newer fluoroquinolones are judged. New clinical indications in complicated skin and skin structure infections, nosocomial pneumonia and chronic bacterial prostatitis continue to expand the important role of this already versatile drug. In addition, the use of 'short-course, high-dose' therapies are being studied in indications, such as community-acquired pneumonia, in an effort to optimize the efficacy and convenience of the drug while minimizing the future development of resistance. As the use of levofloxacin continues to expand, future challenges will include the threat of increasing antimicrobial resistance and the availability of newer alternative agents, both newer fluoroquinolones as well as agents of other antibiotic classes.

[Severe bacterial infection: increased mortality in elderly women with low body weight taking drugs prolonging the QTc interval]

AIMS

Women have a higher risk of acquired long QT syndrome which could be of vital importance in severe bacterial infections when macrolides or fluoroquinolones are administered. This study evaluated whether age, drugs prolonging the QTc interval and body weight were additional influencing factors on mortality in the critically ill with respect to gender.

METHODS

In an exploratory investigation 204 intensive care unit (ICU) patients (78 f, 126 m, 61.1±16.1 years) with severe bacterial infections were studied (mortality probability model II(0) 49.1±28%). Antibiotic therapy was carried out following standard guidelines. In 65.2% of patients potentially QTc prolonging drugs were administered for ≥48 h. Body weight was ascertained on ICU admission.

RESULTS

By comparable severity of illness and comparable effect of antibiotic therapy, age, QTc prolonging drugs and less body weight showed significant effects on survival in women (p<0.001, 0.008 and 0.009, respectively). For women mortality increased with age ≥60 years (p=0.01). The division between survival versus non-survival was intensified by addition of QTc prolonging medication and body weight. As such a best risk assessment in women was achieved if age, QTc prolonging therapy and less body weight were combined (p<0.001). In a direct comparison to men, women with at least two of these factors had a significantly poorer outcome (OR 2.37; 95% CI 1.13-4.98; p=0.022).

CONCLUSIONS

Age, QTc prolonging drugs and lower body weight can additionally increase mortality in critically ill women. If negative outcome is attributed to a higher dosage, an adjustment for body weight must be carried out. Until now it should be considered whether it would be better to replace QTc prolonging antibiotics in routinely performed drug alternation in elderly lean women.

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.

A Review of Levofloxacin for the Treatment of Bacterial Infections

Completing its initial phases of drug development in the mid 1990s as the one of the first fluoroquinolones that could be used with confidence to treat respiratory tract infections, levofloxacin went on to become one of the most widely prescribed antibiotics in the world. Available in both oral (po) and intravenous (IV) formulations and with characteristics of over 90% bioavailability, distribution into both extracellular and intracellular pulmonary compartments, highly predictable pharmacokinetics with over 90% of the drug being excreted unchanged in urine, and reliable activity against a broad spectrum of clinically important pathogens, levofloxacin has been used successfully to treat patients with a variety of serious infectious diseases as well as common infections most often treated outside of the hospital setting. Results of clinical trials involving patients with respiratory tract, urinary tract, and skin infections have consistently shown rates of clinical success and bacteriological eradication that were comparable to other widely used broad-spectrum agents. Regimens of levofloxacin, initially involving total daily doses of 250 mg to 500 mg, but more recently regimens involving 750 mg doses, have been shown to be safe and effective. Nearly a decade and a half of clinical experience has defined a safety and tolerability profile that permits data-driven assessment of the risks and benefits of using levofloxacin. As resistance to currently available fluoroquinolones has emerged, the clinical value of levofloxacin deserves continued evaluation. However, consistently high rates of susceptibility of clinically important bacteria, especially among those bacteria that commonly cause respiratory tract infections, such as Streptococcus pneumoniae and Haemophilus influenzae, suggest that this agent will continue to be a widely used well past the 20-year anniversary of its introduction into the antibacterial armamentarium.

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.

Comparison of 2002–2006 OPTAMA Programs for US Hospitals: Focus on Gram-Negative Resistance

Background:

Resistance among gram-negative bacteria is increasing within the US.

Objective:

To determine pharmacodynamic target attainment rates for 10 antimicrobials against selected gram-negative bacilli and compare these results with previous Optimizing Pharmacodynamic Target Attainment Using the MYSTIC Antibiogram (OPTAMA) assessments.

Methods:

A 5000-patient Monte Carlo simulation using data from population pharmacokinetic studies was employed to estimate the pharmacokinetic profiles for standard and/or prolonged infusion (PI) regimens of cefepime, ceftazidime, ceftriaxone, ciprofloxacin, ertapenem, imipenem, levofloxacin, meropenem, piperacillin–tazobactam, and tigecycline. Minimum inhibitory concentration data were obtained from intensive care units of 15 US hospitals participating in the 2006 MYSTIC (Meropenem Yearly Susceptibility Test Information Collection) study for 640 Escherichia coli, 618 Klebsiella spp., and 606 Pseudomonas aeruginosa isolates. Cumulative fraction of response (CFR) was calculated using pharmacodynamic targets for each antibiotic and compared with results from the 2002 and 2004 OPTAMA studies.

Results:

Against E. coli, CFRs greater than 92% were maintained for all regimens except the fluoroquinolones (CFR range 69.4–72%), which showed a 7% decrease compared with 2004. The presence of Klebsiella spp. producing KPC-type carbapenemases with associated multidrug resistance resulted in a 7% or greater drop in CFR of standard regimens relative to 2004. Despite these resistant phenotypes, high-dose PI regimens (2 g every 8 hours as 3-hour PI) of cefepime and meropenem achieved CFRs of 97% and 95.8%, respectively. Excluding 3 KPC-harboring hospitals resulted in CFR increases to greater than 98% for carbapenems and cefepime and greater than 88% for all other agents tested, except tigecycline. Against P. aeruginosa, the fluoroquinolones had the lowest CFR (55.8–63.9%), followed by imipenem (74.6-80.4%). The most predictable activity was seen with cefepime 2 g every 12 hours or higher (>90%), ceftazidime 2 g every 8 hours (97.9%), and meropenem 1-2 g every 8 hours (86.7–92.6%). Use of PI for piperacillin-tazobactam and meropenem increased CFRs by 6% and 4%, respectively, over standard infusions.

Conclusions:

Relative to previous years, an increase in resistance was noted among gram-negative bacilli to common antibiotics, resulting in disproportionate decreases in pharmacodynamic target attainment. The use of PI for β-lactams may help to overcome these decreases.

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.

Quantitative assessment of combination antimicrobial therapy against multidrug-resistant Acinetobacter baumannii

Treatment of multidrug-resistant bacterial infections poses a therapeutic challenge to clinicians; combination therapy is often the only viable option for multidrug-resistant infections. A quantitative method was developed to assess the combined killing abilities of antimicrobial agents. Time-kill studies (TKS) were performed using a multidrug-resistant clinical isolate of Acinetobacter baumannii with escalating concentrations of cefepime (0 to 512 mg/liter), amikacin (0 to 256 mg/liter), and levofloxacin (0 to 64 mg/liter). The bacterial burden data in single and combined (two of the three agents with clinically achievable concentrations in serum) TKS at 24 h were mathematically modeled to provide an objective basis for comparing various antimicrobial agent combinations. Synergy and antagonism were defined as interaction indices of <1 and >1, respectively. A hollow-fiber infection model (HFIM) simulating various clinical (fluctuating concentrations over time) dosing exposures was used to selectively validate our quantitative assessment of the combined killing effect. Model fits in all single-agent TKS were satisfactory (r(2) > 0.97). An enhanced combined overall killing effect was seen in the cefepime-amikacin combination (interactive index, 0.698; 95% confidence interval [CI], 0.675 to 0.722) and the cefepime-levofloxacin combination (interactive index, 0.929; 95% CI, 0.903 to 0.956), but no significant difference in the combined overall killing effect for the levofloxacin-amikacin combination was observed (interactive index, 0.994; 95% CI, 0.982 to 1.005). These assessments were consistent with observations in HFIM validation studies. Our method could be used to objectively rank the combined killing activities of two antimicrobial agents when used together against a multidrug-resistant A. baumannii isolate. It may offer better insights into the effectiveness of various antimicrobial combinations and warrants further investigations.

A pharmacodynamic simulation to assess tigecycline efficacy for hospital-acquired pneumonia compared with other common intravenous antibiotics

A pharmacodynamic model was used to generate supportive data comparing tigecycline with other broad-spectrum agents against pathogens implicated in hospital-acquired pneumonia (HAP). A 5000 patient Monte Carlo simulation determined the probability of target attainment (PTA) of tigecycline (+/- ceftazidime) compared with imipenem, levofloxacin, and piperacillin/tazobactam (+/- vancomycin). PTA was calculated over MICs of current Gram-positive and Gram-negative bacteria collected from worldwide surveillance and weighted by the expected prevalence of these pathogens causing HAP. For monotherapy, the weighted PTA was imipenem (78.2%), piperacillin/tazobactam (73.3%), tigecycline (62.9%), and levofloxacin (62.5%). By pathogen PTA was greatest for tigecycline against Gram-positives, and ceftazidime or imipenem against Gram-negatives. Combination therapy increased PTA to 88.6%, 85.5%, 80.6%, and 69.8% for tigecycline, imipenem, piperacillin/tazobactam, and levofloxacin, respectively. Based on contemporary resistance data, tigecycline plus ceftazidime is predicted to achieve its pharmacodynamic targets similarly to combination therapy with imipenem plus vancomycin for the treatment of patients with HAP.

Intrapulmonary pharmacodynamics of high-dose levofloxacin in subjects with chronic bronchitis or chronic obstructive pulmonary disease

The objective of this study was to determine the plasma and intrapulmonary pharmacokinetic parameters of intravenously administered levofloxacin in subjects with stable chronic lung disease. Three doses of 1000 mg levofloxacin were administered once daily to 16 adult subjects divided into four groups of 4 subjects each. Standardised bronchoscopy and timed bronchoalveolar lavage (BAL) were performed at 4 h, 8 h, 12 h and 24 h following administration of the last dose. Blood was obtained for drug assay prior to drug administration, at the end of the last infusion (maximum concentration (Cmax)) and at the time of BAL. Levofloxacin was measured using a high-performance liquid chromatographic tandem mass spectrometric (HPLC/MS/MS) technique. Plasma, epithelial lining fluid (ELF) and alveolar cell (AC) pharmacokinetics were derived using non-compartmental methods. Cmax/MIC(90) and area under the concentration-time curve for 0-24 h after the last dose (AUC(0-24 h)/MIC(90) ratios were calculated for respiratory pathogens with minimum inhibitory concentrations for 90% of the organisms (MIC(90)) of 0.03-2 microg/mL. The Cmax (mean+/-standard deviation), AUC(0-24h) and half-life were, respectively, 9.2+/-2.7 microg/mL, 130 microg h/mL and 8.7 h for plasma, 22.8+/-12.9 microg/mL, 260 microg h/mL and 7.0 h for ELF and 76.3+/-28.7 microg/mL, 1492 microg h/mL and 49.5 h for ACs. Levofloxacin concentrations were quantitatively greater in ACs than in ELF or plasma at all time points, however only the differences between AC concentration and ELF or plasma concentrations in the 4-h and 8-h time groups were statistically significant. Cmax/MIC(90) and AUC/MIC(90) ratios in ELF were, respectively, 11.4 and 130 for Mycoplasma pneumoniae, 22.8 and 260 for Streptococcus pneumoniae, 91.2 and 1040 for Chlamydia pneumoniae and 760 and 8667 for Haemophilus influenzae. In ACs the ratios were 38.2 and 746 for M. pneumoniae, 76.3 and 1492 for S. pneumoniae, 305 and 5968 for C. pneumoniae and 2543 and 49 733 for H. influenzae. In conclusion, Cmax/MIC(90) and AUC/MIC(90) ratios provide a pharmacokinetic rationale for once-daily administration of a 1000 mg dose of levofloxacin and are favourable for the treatment of respiratory infection in patients with chronic lung disease.

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.

Evaluation of gatifloxacin pharmacokinetics and pharmacodynamics in severely ill adults in a medical Intensive Care Unit

A prospective, open-label study investigated the steady-state pharmacokinetics of gatifloxacin in 20 adult patients in a medical Intensive Care Unit (ICU). Twelve patients had normal or moderately impaired renal function (creatinine clearance (CrCL) >or=40 mL/min) and received gatifloxacin 400 mg intravenously once daily. Eight patients had CrCL<40 mL/min and received 200 mg doses. Gatifloxacin plasma and urine concentrations were determined by validated high-performance liquid chromatography. Mean+/-standard deviation gatifloxacin elimination half-life (t(1/2)), systemic clearance and volume of distribution in patients with CrCL>or=40 mL/min were 10.8+/-1.5h, 156+/-29 mL/min and 1.8+/-0.2 L/kg, respectively. Maximum and minimum serum concentrations (C(max) and C(min)) and area under the serum concentration-time curve from 0-24 h (AUC(0-24)) in these patients were 4.77+/-0.76 mg/L, 1.08+/-0.28 mg/L and 44.4+/-9.2 mgh/L, respectively. Observed t(1/2), C(max) and AUC(0-24) following 200 mg doses in patients with poor renal function (CrCL<40 mL/min) were 18.2+/-3.3 h, 2.85+/-0.76 mg/L and 36.6+/-3.4 mgh/L, respectively. Statistically significant (P<0.05) increase in AUC(0-24) and decreases in t(1/2) and clearance (total and renal) were observed in ICU patients administered intravenous gatifloxacin compared with previous data in healthy volunteers. Pharmacodynamic evaluation by Monte Carlo simulation indicated that approved gatifloxacin dosage regimens appear to be adequate for most pathogens (minimum inhibitory concentration (MIC) <or=0.5 microg/mL) associated with community-acquired infections in severely ill ICU patients; less susceptible pathogens (MIC>or=1 microg/mL) do not appear to be optimally treated with currently approved doses.

Reevaluation of current susceptibility breakpoints for Gram-negative rods based on pharmacodynamic assessment

Although pharmacodynamic (PD) modeling is now being considered for decision support for susceptibility breakpoint determination against Gram-negative bacteria, these PD-derived breakpoints should be verified using a clinically applicable population of organisms. In this analysis, a 5000-patient Monte Carlo simulation was used to determine PD breakpoints, the highest 2-fold MIC in which the probability of bactericidal target attainment (PTA) remained > or = 90%. Percent susceptibilities for 639 Pseudomonas aeruginosa, 103 Acinetobacter baumannii, 705 Escherichia coli, and 418 Klebsiella spp. collected during the 2004 Meropenem Yearly Susceptibility Test Information Collection surveillance study were then defined according to the PD-derived breakpoint (%S(PD)) and compared with the current Clinical Laboratory Standards Institute (CLSI)-defined breakpoints (%S(CLSI)). %S(PD) and %S(CLSI) were compared with the bactericidal PTA for each pathogen population to determine the degree of agreement. Resulting PD breakpoints were drug and dose dependent; moreover, values were commonly 2 to 4 MIC dilutions lower than CLSI breakpoints. Overall, %S(PD) more closely agreed with the PTA for the tested beta-lactam and fluoroquinolone dosing regimens. In contrast, %S(CLSI) overestimated PTA for many dosing regimens, especially against Pseudomonas: piperacillin/tazobactam 4.5 g qid (+9.7%), ciprofloxacin 0.4 g bid (+13.7%) and 0.4 g tid (+9.3%), and levofloxacin 0.5 g every 24 h (+22.4%) and 0.75 g every 24 h (+9.9%). Differences were most pronounced against the nonfermenting Gram-negative bacteria and were not observed among the Enterobacteriaceae. As a result, a new method of breakpoint classification is proposed, which is dosing regimen and pathogen specific, and is designed to denote isolates as susceptible only if target bactericidal exposures are achievable with the dosing regimen selected.

Pharmacodynamic Target Attainment of Six β-Lactams and Two Fluoroquinolones AgainstPseudomonas aeruginosa,Acinetobacter baumannii,Escherichia coli, andKlebsiellaSpecies Collected from United States Intensive Care Units in 2004

STUDY OBJECTIVE

To determine the likelihood that antibiotic regimens achieve bactericidal pharmacodynamic exposures against common nosocomial pathogens.

DESIGN

Pharmacodynamic Monte Carlo simulation model.

DATA SOURCE

Microbiologic data generated from isolates from the 14 centers in the United States in the 2004 Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) surveillance study.

PATIENTS

Five thousand simulated patients with infection.

MEASUREMENTS AND MAIN RESULTS

Pharmacokinetic profiles of the patients were simulated to determine the bactericidal cumulative fraction of response (CFR) for commonly used intravenous regimens of cefepime, ceftazidime, ceftriaxone, ciprofloxacin, imipenem, levofloxacin, meropenem, and piperacillin-tazobactam against Pseudomonas aeruginosa, Acinetobacter baumannii, Escherichia coli, and Klebsiella species. Ciprofloxacin and levofloxacin had CFRs among the lowest of all drugs against all pathogens, especially P. aeruginosa (40.4-65.5%) and A. baumannii (43.6-48.2%). The low CFR of about 78% against E. coli with these two agents was of particular concern. Among the beta-lactams, only high-dose cefepime and ceftazidime regimens achieved CFRs of greater than 90% against P. aeruginosa, followed by cefepime 2 g every 12 hours and the carbapenems (86.3-89.7%). No regimen achieved an optimum CFR for A. baumannii. All beta-lactam regimens achieved a greater-than-90% likelihood of having bactericidal CFRs against Enterobacteriaceae.

CONCLUSION

Because of the continual evolution of resistance among gram-negative bacteria in the United States, reevaluation of optimum dosing strategies for beta-lactam and fluoroquinolone antibiotics is necessary.

Estudio de la actividad comparada de varias fluoroquinolonas frente a Pseudomonas aeruginosa mediante la determinación de la concentración preventiva de mutantes

INTRODUCTION

The objective of this study was to compare the activity of ciprofloxacin, levofloxacin, moxifloxacin, gatifloxacin and ofloxacin against Pseudomonas aeruginosa by determining the mutant prevention concentration (MPC).

METHODS

Thirty-four clinical isolates of Pseudomonas aeruginosa causing nosocomial infection were studied. MPC values were determined using an inoculum of 10(10) cfu/mL on Mueller-Hinton plates with serial dilutions of the antibiotics. The microorganisms were classified according to whether the patients had been previously treated with fluoroquinolones or not.

RESULTS

The fluoroquinolone with the lowest MPC values was ciprofloxacin, followed by levofloxacin. Analysis of strains from patients previously treated with fluoroquinolones showed persistent susceptibility according to the CLSI criteria, but with lower activity of all the drugs.

CONCLUSIONS

Although the microorganism remained susceptible to fluoroquinolones according to classical methods, the suitability of using these drugs in patients with severe infection and a history of fluoroquinolone use should be evaluated.

Oral antibiotic therapy of serious systemic infections

Traditionally, antibiotics have been administered intravenously (IV) for serious systemic infections. As more potent oral antibiotics were introduced, and their pharmacokinetic aspects studied, orally administered antibiotics have been increasingly used for serious systemic infections. Antibiotics ideal for oral administration are those that have the appropriate spectrum, high degree of activity against the presumed or known pathogen, and have good bioavailability. Oral antibiotics with high bioavailability, that is > or = 90% absorbed, achieve serum/tissue concentrations comparable to IV administered antibiotics at the same dose. The popularity of "IV to PO switch therapy" is possible because of the availability of many potent oral antibiotics with high bioavailability. Initial IV therapy is appropriate in patients who are in shock/have impaired intestinal absorption, but after clinical defervescence, completion of therapy should be accomplished with oral antibiotics. As experience with "IV to PO switch therapy" has accumulated, confidence in oral antimicrobics for therapy of serious systemic infections has continued to increase. The trend in treating serious systemic infections entirely with oral antimicrobial therapy will continue, and is clearly the wave of the future.