Optimizing pharmacodynamic target attainment using the MYSTIC antibiogram: data collected in North America in 2002

Population Pharmacokinetics of Doxycycline, Administered Alone or with N-Acetylcysteine, in Chickens with Experimental Mycoplasma gallisepticum Infection

Mycoplasmosis is a bacterial infection that significantly affects poultry production, and it is often controlled with antibiotics, including doxycycline. The conducted study aimed to determine population pharmacokinetic (PopPk) parameters of doxycycline in healthy (n = 12) and in Mycoplasma gallisepticum-challenged (n = 20) chickens after its oral administration via drinking water at the registered dose rate of 20 mg/kg b.w./24 h for five days, without or with co-administration of N-acetylcysteine (NAC, a dose of 100 mg/kg b.w./24 h) via the feed. Doxycycline concentrations in plasma were analyzed with the LC-MS/MS method. The values of tvV/F and tvke were 4.73 L × kg−1 and 0.154 h−1, respectively, and they showed low BSV. A high BSV of 93.17% was calculated for the value of tlag of 0.8 h, which reflects the inter-individual differences in the water consumption. PTA was computed after Monte Carlo simulation with the registered dose for doxycycline. The target of %fT > MIC ≥ 80% and 100% can be achieved in 90% of the broiler population, after a correction for protein binding, for bacteria with MIC ≤ 0.5 mg × L−1 and 0.25 mg × L−1, respectively. The applied PopPk model did not reveal significant effect of M. gallisepticum infection and co-administration of NAC on pharmacokinetic parameters of doxycycline.

Dosage Adjustment for Ceftazidime in Pediatric Patients With Renal Impairment Using Physiologically Based Pharmacokinetic Modeling

Physiologically based pharmacokinetic (PBPK) modeling has unique advantages in investigating the pharmacokinetics of drugs in special populations. Our aim is to design optimized dosing regimens for ceftazidime in renally-impaired pediatric patients using PBPK modeling. Models for healthy and renally-impaired adults were developed, verified, and adapted for children to predict ceftazidime exposure in pediatric patients with varying degrees of renal impairment, capturing age- and weight-related pharmacokinetic changes. We derived a dosage-adjusted regimen for renally-impaired children based on pharmacokinetic data and evaluated the pharmacodynamics of ceftazidime. The PBPK models adequately predicted ceftazidime exposures in populations after single- and multi-dose administrations, with fold error values within 1.1 between simulated and observed data. In moderate, severe, and end-stage renally-impaired pediatric patients, the areas under the plasma concentration-time curves (AUCs) were 1.87-fold, 3.56-fold, and 6.19-fold higher, respectively, than in healthy children when treated with the same dose of 50 mg/kg. Pharmacodynamic verification indicated that the recommended doses of 28, 15, and 8 mg/kg administered three times daily (every 8 h) to pediatric patients with moderate, severe, and end-stage renal disease, respectively, were sufficient to attain the target of maintaining the free plasma concentration at or above minimum inhibitory concentration (MIC) during 70% of the dosing interval (70% fT > MIC: nearly 100% target attainment for susceptible MIC of 4 mg/L and >70% for intermediate MIC of 8 mg/L). Our PBPK model can be an effective tool to support dosing recommendations in pediatric patients with different degrees of renal impairment.

Population pharmacokinetics and target attainment of ciprofloxacin in critically ill patients

Purpose

To develop and validate a population pharmacokinetic model of ciprofloxacin intravenously in critically ill patients, and determine target attainment to provide guidance for more effective regimens.

Methods

Non-linear mixed-effects modelling was used for the model development and covariate analysis. Target attainment of an ƒAUC_0–24/MIC ≥ 100 for different MICs was calculated for standard dosing regimens. Monte Carlo simulations were performed to define the probability of target attainment (PTA) of several dosing regimens.

Results

A total of 204 blood samples were collected from 42 ICU patients treated with ciprofloxacin 400–1200 mg/day, with median values for age of 66 years, APACHE II score of 22, BMI of 26 kg/m², and eGFR of 58.5 mL/min/1.73 m². The median ƒAUC_0–24 and ƒC_max were 29.9 mg•h/L and 3.1 mg/L, respectively. Ciprofloxacin pharmacokinetics were best described by a two-compartment model. We did not find any significant covariate to add to the structural model. The proportion of patients achieving the target ƒAUC_0–24/MIC ≥ 100 were 61.9% and 16.7% with MICs of 0.25 and 0.5 mg/L, respectively. Results of the PTA simulations suggest that a dose of ≥ 1200 mg/day is needed to achieve sufficient ƒAUC_0–24/MIC ratios.

Conclusions

The model described the pharmacokinetics of ciprofloxacin in ICU patients adequately. No significant covariates were found and high inter-individual variability of ciprofloxacin pharmacokinetics in ICU patients was observed. The poor target attainment supports the use of higher doses such as 1200 mg/day in critically ill patients, while the variability of inter-individual pharmacokinetics parameters emphasizes the need for therapeutic drug monitoring to ensure optimal exposure.

Electronic supplementary material

The online version of this article (10.1007/s00228-020-02873-5) contains supplementary material, which is available to authorized users.

Pharmacokinetic modeling and simulation for dose rationale of doripenem in neonates and infants

The aims of this study were to construct a population pharmacokinetic model of doripenem in neonates and infants and to assess the dosing regimen for patients <3 months of age using Monte-Carlo pharmacokinetic/pharmacodynamic (PKPD) simulations. In the population pharmacokinetic analysis using 187 plasma concentrations from 47 neonates and infants, a two-compartment model well described plasma doripenem concentrations with the most significant covariates of chronological age and gestational age identified for the pharmacokinetics of doripenem. Monte-Carlo simulations suggested that the selected dosages for neonates and infants based on chronological age and gestational age (5 or 10 mg/kg) would provide ≥90% target attainment of 40%fT_>MIC against MIC of 2 μg/mL in all age groups. These results would be useful for understanding the PKPD characteristics of doripenem, which could provide essential information on optimal therapeutic treatment for neonates and infants.

Pharmacokinetic and pharmacodynamic profiling of four antimicrobials against Acinetobacter baumannii infection

BACKGROUND

The aim of this study was to evaluate common antimicrobial regimens used in eradicating Acinetobacter baumannii in Shenyang, China.

METHODS

Monte Carlo simulation was conducted to estimate the probability target attainment (PTA) and cumulative fraction of response (CFR) for imipenem, cefoperazone/sulbactam (2:1), tigecycline and colistin methanesulfonate.

RESULTS

For the results of PTAs, imipenem following administration of 0.5 g q6 h, 1 g q8 h, and 1 g q6 h for both 0.5 h and 2 h infusion achieved＞90% PTAs when MIC was 8 μg/ml; cefoperazone/ sulbactam (2:1) following administration of 4.5 g q6 h and 6 g q6 h achieved＞90% PTAs when MIC was 64μg/ml; tigecycline following administration of 50 mg q12 h and 100 mg q12 h achieved＞90% PTAs when MIC was 1 μg/ml; colistin methanesulfonate with high dosages (3MU q8 h) could provide high PTA (95.13%) in patients with CL_Cr＜60 ml/min when MIC was 2 μg/ml. As for CFR values of four antibiotics, imipenem achieved the lowest CFR values. For cefoperazone/sulbactam (2:1) and tigecycline, with simulated regimens improvement, the CFR values were both increased, and there were obviously increasing CFR values against Acinetobacter baumannii. For colistin methanesulfonate, the most aggressive dosage of 3MU q8 h could provide satisfactory CFR values (≥86.94%) against Acinetobacter baumannii in patients at various CL_Cr.

CONCLUSION

This study suggested that measurement of MICs, individualized therapy and therapeutic drug-level monitoring should be considered together to achieve the optimal drug exposure. That will provide the best chance of achieving the highest probability of a successful clinical or microbiological response, and avoiding the induced resistance.

Transport of Vancomycin and Cefepime Into Human Intervertebral Discs: Quantitative Analyses

STUDY DESIGN

Simulation of antibiotics transport into human intervertebral disc with intravenous infusion.

OBJECTIVE

The objective of this study was to quantitatively investigate antibiotic concentrations in the disc.

SUMMARY OF BACKGROUND DATA

Intravenous infusion of antibiotics is typically used to treat intervertebral disc infection in clinics. However, it is difficult to evaluate the drug concentrations within discs in vivo.

METHODS

A computational model was used in this study. The variation of drug charge with pH was considered in the model. Thirty-minute infusions of two commonly used antibiotics in clinic-vancomycin and cefepime-were numerically investigated. Spatial and temporal concentration distributions of these drugs in both nondegenerated and moderately degenerated discs were calculated.

RESULTS

For intravenous infusion of 1 g vancomycin and 2 g cefepime in 30 minutes repeated every 12 hours, it was predicted that vancomycin concentration in the disc fluctuated between 17.0 and 31.0 times of its minimum inhibitory concentration (1 ug/mL) and cefepime concentration fluctuated between 1.1 and 4.2 times of its minimum inhibitory concentration (i.e., 8 ug/mL) in about 2 days. It was also found that vancomycin concentration in moderately degenerated disc was lower than that in the nondegenerated disc.

CONCLUSION

This study provides quantitative guidance on selecting proper dosage for treating disc infection. The method used in this study could be used to provide quantitative information on transport of other antibiotics and drugs in discs as well.

LEVEL OF EVIDENCE

N/A.

Simulating moxalactam dosage for extended-spectrum β-lactamase-producing Enterobacteriaceae using blood antimicrobial surveillance network data

Objectives: Monte Carlo simulation (MCS) was used to evaluate optimal dosage for cefepime (FEP), moxalactam (MOX), and cefperazone/sulbactam (CFZ/SBT) against extended-spectrum β-lactamase (ESBL) producers isolated from the Blood Bacterial Resistant Investigation Collaborative System.

Methods: Minimum inhibitory concentration (MIC) was tested by agar dilution, and ESBL producers were identified by modified Clinical and Laboratory Standards Institute tests. Pharmacokinetic parameters were derived from data on healthy individuals, and probability of target attainment (PTA) and cumulative fraction of response (CFR) %fT >MIC values were estimated by MCS.

Results: A total of 2032 Escherichia coli (875 ESBL-producing) and Klebsiella pneumoniae (157 ESBL-producing) strains, and 371 other Enterobacteriaceae strains, were isolated from patients with bloodstream infections (BSIs). MIC₉₀ values for FEP, MOX, and CFZ/SBT against ESBL-producing E. coli and K. pneumoniae were 64/64 mg/L, 2/32 mg/L, and 64/128 mg/L, respectively. Conventional MOX and CFZ/SBT doses failed to reach 90% PTA against isolates with MICs ≥8 mg/L and ≥4 mg/L, respectively. Against ESBL producers, neither FEP nor CFZ/SBT achieved ≥90% CFR, while CFRs for MOX (1 g iv q6h, 2 g iv q12h, and 2 g iv q8h) exceeded 90% against ESBL-producing E. coli. Simulated CFRs for FEP and MOX were similar (>90%) against non-ESBL-producing Enterobacteriaceae, and higher than CFRs for CFZ/SBT.

Conclusion: ESBL producers from BSIs were highly susceptible to MOX, and PTA values were generally higher for MOX than FEP or CFZ/SBT for conventional dosing regimens. This large MCS analysis shows that MOX but not FEP or CFZ/SBT can be used empirically to treat BSIs caused by ESBL-producing E. coli strains.

Population Pharmacokinetics of Doripenem in Pediatric Patients and Monte-Carlo Pharmacokinetic-Pharmacodynamic Simulations for Dosing Regimen Assessment

The aims of this study were to evaluate the pharmacokinetics of doripenem (Finibax^®, Doribax^®, S-4661), a parenteral carbapenem antibiotic, in pediatric patients based on concentrations of doripenem in plasma after administration of 20 mg/kg 2 or 3 times daily and to evaluate the dosing regimens by using Monte-Carlo pharmacokinetic-pharmacodynamic simulations. Population pharmacokinetic analysis was performed by using 190 plasma concentrations of doripenem from 99 patients (2 months-13 years old). The two-compartment model well described the doripenem plasma concentrations in pediatric patients. Body weight was found to be the most significant influential factor. Gender was also found to be a significant covariate although the effect was relatively small. Monte-Carlo simulations indicated that 20 mg/kg over 1 h infusion would give 90% probability of target attainment for 40% of time above minimum inhibitory concentration against Haemophilus influenzae and Streptococcus pneumoniae, major causative pathogens in pediatric infections, and that 40 mg/kg, the highest approved dose for Japanese pediatric patients, administered over 3 h infusion achieved 98.6% against 8 μg/mL. The developed population pharmacokinetic model of doripenem and Monte-Carlo simulations for pediatric patients should provide useful information for understanding the pharmacokinetic and pharmacokinetic-pharmacodynamic characteristics of doripenem and for optimal treatment of pediatric patients.

Therapeutic Drug Monitoring of Beta-Lactams and Other Antibiotics in the Intensive Care Unit: Which Agents, Which Patients and Which Infections?

Antibiotics are among the medications most frequently administered to the critically ill, a population with high levels of intra- and inter-individual pharmacokinetic variability. Our knowledge of the relationships among antibiotic dosing, exposure and clinical effect in this population has increased in recent decades. Therapeutic drug monitoring (TDM) of serum antibiotic concentrations is the most practical means of assessing adequate antibiotic exposure, though until recently, it has been underutilised for this end. Now TDM is becoming more widespread, particularly for the beta-lactam antibiotics, a class historically thought to have a wide therapeutic range. We review the basic requirements, indications, and targets for effective TDM of the glycopeptides, aminoglycosides, quinolones and beta-lactam antibiotics in the adult intensive-care setting, with a special focus on TDM of the beta-lactam antibiotics, the most widely used antibiotic class.

Prediction of Pharmacokinetics and Pharmacodynamics of Doripenem in Pediatric Patients

The aim of this paper was to predict the pharmacokinetics of doripenem in pediatrics from adult pharmacokinetic data and to investigate dosing regimens in pediatrics using Monte-Carlo pharmacokinetics/pharmacodynamics (PK/PD) simulations prior to the initiation of pediatric clinical trials. The pharmacokinetics in pediatrics was predicted by using a previously reported approach for β-lactam antibiotics. Monte-Carlo simulation was employed to assess dosing regimens in pediatrics based on the predicted pharmacokinetic profiles and the minimum inhibitory concentration (MIC) distributions of Haemophilus influenzae and Streptococcus pneumoniae, which frequently cause infectious pediatric diseases. The probabilities of attaining target time above MIC (40%T>MIC) were calculated for dosing regimens of 1-30 mg/kg with two or three times daily dosing (TID) based on simulations of 5000 pediatric patients and MICs. The results suggested 15 and 5 mg/kg TID would give approximately 90% or more probability of target attainment against Haemophilus influenzae and Streptococcus pneumoniae, respectively. The pediatric phase 3 study confirmed that pharmacokinetics in pediatrics could be well predicted by this method, indicating that the dosing regimen had been appropriately selected. The framework of dose selection for pediatric clinical trials based on predictions of pharmacokinetic profiles and PK/PD indices should be applicable to the development of other β-lactam antibiotics for pediatric use.

Evaluation of clinical outcomes in patients with Gram-negative bloodstream infections according to cefepime MIC

Predicted and observed failures at higher cefepime MICs have prompted the Clinical and Laboratories Standards Institute (CLSI) to lower the susceptible breakpoint for Enterobacteriaceae to ≤2mg/L, with dose-dependent susceptibility at 4-8mg/L, while the susceptibility breakpoint for nonfermentative organisms remain unchanged at ≥8mg/L. The contribution of increasing cefepime MIC to mortality risk in the setting of aggressive cefepime dosing is not well defined. Patients who were treated with cefepime for Gram-negative blood stream infections (GNBSIs), including both Enterobacteriaceae and nonfermentative organisms, were screened for inclusion in this retrospective cohort study. Demographic and microbiologic variables were collected, including pathogen, cefepime MIC, dosage, and interval. The objective was to define a risk-adjusted mortality breakpoint for cefepime MICs. Secondarily, we looked at time to death and length of stay (LOS) postculture. Ninety-one patients were included in the analysis. Overall, 19 patients died and 72 survived. Classification and Regression Tree analysis identified an inhospital mortality breakpoint at a cefepime MIC between 2 and 4mg/L for patients with a modified Acute Physiology and Chronic Health Evaluation II score ≤16.5 (4.2% versus 25%, respectively). Multivariate logistic regression revealed increased odds of mortality at a cefepime MIC of 4mg/L (adjusted odds ratio [aOR] 6.47; 95% confidence interval [CI] 1.25-33.4) and 64mg/L (aOR 6.54, 95% CI 1.03-41.4). Those with cefepime MICs ≥4mg/L experienced a greater median intensive care unit LOS for survivors (16 versus 2days; P=0.026). Increasing cefepime MIC appears to predict inhospital mortality among patients who received aggressive doses of cefepime for GNBSIs, supporting a clinical breakpoint MIC of 2mg/L.

Evaluating outcomes of alternative dosing strategies for cefepime: a qualitative systematic review

OBJECTIVE

To perform a qualitative systematic review of the evidence comparing traditional with prolonged intermittent or continuous infusions of cefepime based on clinical and pharmacodynamic outcomes.

DATA SOURCES

PubMed (1946 to October 2014), EMBASE (1980 to October 2014), CENTRAL, Cochrane Database of Systematic Reviews, Web of Science, and International Pharmaceutical Abstracts (1970 to October 2014) were searched using the terms cefepime, pharmacokinetics, pharmacodynamics, drug administration, intravenous infusions, intravenous drug administration, continuous infusion, extended infusion, and intermittent therapy. Reference lists from relevant materials were reviewed.

STUDY SELECTION AND DATA EXTRACTION

Articles evaluating administration regimens of cefepime, one of which included the traditional, manufacturer-recommended 0.5-hour infusion and the other a prolonged or continuous infusion were included. Prespecified clinical outcomes of interest included all-cause mortality, length of hospital stay, clinical cure, and adverse events. The primary pharmacodynamic outcome was percentage time of unbound drug concentration remaining above the minimum inhibitory concentration.

DATA SYNTHESIS

In all, 18 studies were included; 6 studies assessed clinical outcomes, and 12 assessed pharmacodynamic outcomes. Prolonged or continuous infusions of cefepime achieved the pharmacodynamic targets more often than traditional infusions. The association of improved clinical outcomes with prolonged or continuous infusions is unclear. All-cause mortality was significantly decreased with the use of a prolonged cefepime infusion in a retrospective study. Two prospective, randomized studies demonstrated no statistically significant difference in mortality between prolonged and intermittent infusions.

CONCLUSIONS

The available literature on prolonged and continuous infusions of cefepime demonstrated an improved achievement of pharmacodynamic targets; however, the effect on clinical outcomes is inconclusive. Well-designed prospective studies are required to determine optimal dosing and administration strategies.

Pharmacokinetics and pharmacodynamics of aerosolized antibacterial agents in chronically infected cystic fibrosis patients

Bacteria adapt to growth in lungs of patients with cystic fibrosis (CF) by selection of heterogeneously resistant variants that are not detected by conventional susceptibility testing but are selected for rapidly during antibacterial treatment. Therefore, total bacterial counts and antibiotic susceptibilities are misleading indicators of infection and are not helpful as guides for therapy decisions or efficacy endpoints. High drug concentrations delivered by aerosol may maximize efficacy, as decreased drug susceptibilities of the pathogens are compensated for by high target site concentrations. However, reductions of the bacterial load in sputum and improvements in lung function were within the same ranges following aerosolized and conventional therapies. Furthermore, the use of conventional pharmacokinetic/pharmacodynamic (PK/PD) surrogates correlating pharmacokinetics in serum with clinical cure and presumed or proven eradication of the pathogen as a basis for PK/PD investigations in CF patients is irrelevant, as minimization of systemic exposure is one of the main objectives of aerosolized therapy; in addition, bacterial pathogens cannot be eradicated, and chronic infection cannot be cured. Consequently, conventional PK/PD surrogates are not applicable to CF patients. It is nonetheless obvious that systemic exposure of patients, with all its sequelae, is minimized and that the burden of oral treatment for CF patients suffering from chronic infections is reduced.

Comparison of the probability of target attainment of anidulafungin against Candida spp. in patients with acute leukaemia

This study aimed to investigate the probability of target attainment (PTA) of various anidulafungin dosing regimens against Candida spp. in patients with acute leukaemia. A Monte Carlo simulation was performed using a previously published population pharmacokinetic model. The following dosing scenarios were evaluated: 200 mg loading dose (LD) on Day 1 then 100 mg daily (manufacturer's recommended dosing regimen); 200 mg LD on Day 1 then 100 mg every 48 h (q48 h); and 200 mg q48 h, 200 mg every 72 h (q72 h) and 300 mg q72 h. For each dosing regimen, free drug concentrations were calculated to evaluate the effect of 99% protein binding. The PTA at various pharmacodynamic (PD) targets was determined as the percentage of subjects who achieved a free drug area under the plasma concentration-time curve over the minimum inhibitory concentration ratio (ƒAUC/MIC) or a free drug maximum plasma concentration over the minimum inhibitory concentration ratio (ƒC(max)/MIC) above the PD targets. PTA expectation values were then calculated for each dosing regimen. The currently recommended dosing regimen of anidulafungin was not optimal for invasive candidiasis in patients with acute leukaemia. Alternate dosing strategies with higher doses and extended dosing intervals (intermittent dosing) achieved better target attainment. This is the first study to optimise therapy with anidulafungin using Monte Carlo simulation. These results provide a rationale in support of future clinical investigation of intermittent dosing of anidulafungin.

Prolonging β-lactam infusion: a review of the rationale and evidence, and guidance for implementation

Given the sparse antibiotic pipeline and the increasing prevalence of resistant organisms, efforts should be made to optimise the pharmacodynamic exposure of currently available agents. Prolonging the infusion duration is a strategy used to increase the percentage of the dosing interval that free drug concentrations remain above the minimum inhibitory concentration (fT>MIC), the pharmacodynamic efficacy driver for time-dependent antibiotics such as β-lactams. β-Lactams, the most commonly prescribed class of antibiotics owing to their efficacy and safety profile, have been the mainstay of therapy since the discovery of penicillin over 60 years ago. Mounting evidence, including the use of population pharmacokinetic modelling and Monte Carlo simulation, suggests that prolonging the infusion time of β-lactam antibiotics may have advantages over standard infusion techniques, including an enhanced probability of achieving requisite fT>MIC exposures, lower mortality and potentially reductions in infection/antibiotic-related costs. As a result of these favourable attributes, clinical practice guidelines support the use of prolonged-infusion β-lactams in the treatment of many severe infections. This article discusses the rationale and evidence for prolonging the infusion of β-lactam antibiotics and provides guidance for the implementation of a prolonged-infusion programme.

Pharmacodynamic target attainment for various ceftazidime dosing schemes in high-flux hemodialysis

Ceftazidime is a broad-spectrum cephalosporin with high-level activity against a variety of Gram-negative pathogens, including Pseudomonas aeruginosa. Improved outcomes are associated with cumulative percentages of a 24-h period that the drug concentration exceeds the MIC under steady-state pharmacokinetic conditions (%TMIC) of >45 to 70% of the dosing interval. Optimal dosing to achieve a 90% probability of target attainment (PTA) in patients receiving high-flux hemodialysis (HFHD) is unknown. We used existing data from six anephric adults receiving hemodialysis to construct a population model with the Pmetrics package for R. From the final model's joint probability density, we simulated the PTA for various ceftazidime dosing regimens, HFHD schedules, and organism MICs. For HFHD every 48 h and 1 g of ceftazidime given posthemodialysis, the PTA exceeds 90% for all isolates with MICs of ≤8 μg/ml, assuming a goal of 70%TMIC. For 72-h dialysis intervals, postdialysis dosing of 1 g is adequate for achievement of the 70%TMIC goal only for organisms with MICs of ≤4 μg/ml, while 2 g is adequate for organisms with MICs of ≤8 μg/ml. A dose of 500 mg once daily, regardless of HFHD schedule, has a 90% PTA for organisms with MICs of ≤16 μg/ml, while 1 g once daily may achieve 100% PTA even for resistant organisms with a MIC of 32 μg/ml. Therefore, to ensure maximal ceftazidime activity, once-daily dosing of 500 mg to 1 g ceftazidime in patients receiving HFHD may be preferable for critically ill patients when MIC data are unavailable and for more resistant organisms with ceftazidime MICs of 16 to 32 μg/ml.

Pharmacodynamic profiling of doripenem, imipenem and meropenem against prevalent Gram-negative organisms in the Asia-Pacific region

Carbapenems are increasingly being utilised owing to the escalating prevalence of antimicrobial-resistant Gram-negative bacteria from community and hospital settings. In this study, pharmacodynamic profiles of doripenem, imipenem and meropenem were evaluated against Gram-negative bacteria isolated from hospitalised patients. MICs for carbapenems were determined for Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii obtained from the COMPACT II programme conducted in the Asia-Pacific region. Monte Carlo simulations were undertaken to assess the pharmacodynamic profile of carbapenems against each of the pathogens. All carbapenem regimens achieved optimal exposures [cumulative fraction of response (CFR) ≥90%] against E. coli and K. pneumoniae. Against P. aeruginosa, doripenem achieved 81.3-95.3% CFR, imipenem achieved 55.2-77.9% CFR and meropenem achieved 71.9-91.3% CFR; only doripenem regimens of 4-h infusion of 1000 mg every 8h (q8h) and 1-h and 4-h infusion of 2000 mg q8h and a meropenem regimen of 3-h infusion of 2000 mg q8h obtained optimal exposures; all carbapenem regimens showed slight (1-7%) improvement in CFRs in favour of isolates collected from ICU sources. Against A. baumannii, CFRs were much lower (25.9-46.7% CFR) and no carbapenem regimens achieved optimal exposure in or outside the ICU. Owing to the high potency of carbapenems against these Enterobacteriaceae populations, standard regimens are likely to perform well in the Asia-Pacific region. However, larger doses combined with prolonged infusions will be required to increase the CFR for these carbapenems against resistant non-fermenting Gram-negatives such as P. aeruginosa and A. baumannii that are prevalent in these countries.

Population pharmacokinetics of piperacillin at two dose levels: influence of nonlinear pharmacokinetics on the pharmacodynamic profile

Piperacillin in combination with tazobactam is one of the most commonly used intravenous antibiotics. There is evidence for a possible saturable elimination of piperacillin. Therefore, the saturable elimination and its impact on the choice of optimal dosage regimens were quantified. In a randomized crossover study, 10 healthy volunteers received 1,500 mg and 3,000 mg of piperacillin as 5-min intravenous infusion. Population pharmacokinetics based on plasma and urine data were determined utilizing NONMEM and S-ADAPT. Probabilities of target attainment (PTAs) were compared for different models and dosage regimens, based on the target time of the non-protein-bound concentration above the MIC of at least 50% of the dosing interval. Total clearance of piperacillin was 18% (geometric mean ratio, 90% confidence interval, 11 to 24%) lower (P < 0.01), and renal clearance was 24% (9 to 37%) lower (P = 0.02) at the high compared to the low dose. The final model included first-order nonrenal elimination and parallel first-order and mixed-order renal elimination. Nonrenal clearance was 5.44 liter/h (coefficient of variation, 18%), first-order renal clearance was 4.42 liter/h (47%), and the maximum elimination rate of mixed-order renal elimination was 219 mg/h (84%), with a Michaelis-Menten constant of 36.1 mg/liter (112%). Compared to models with saturable elimination, a linear model predicted up to 10% lower population PTAs for high-dose short-term infusions (6 g every 8 h) and up to 4% higher population PTAs for low-dose continuous infusions (6 g/day). While renal elimination of piperacillin was saturable at therapeutic concentrations, the extent of saturation of nonrenal clearance was small. The influence of saturable elimination on PTAs for clinically relevant dosage regimens was relatively small.

Intraperitoneal clearance as a potential biomarker of cisplatin after intraperitoneal perioperative chemotherapy: a population pharmacokinetic study

Background:

Intraperitoneal (IP) perioperative chemotherapy with cisplatin is an interesting option in ovarian cancer treatment. A combination of cisplatin with IP epinephrine (already shown to improve IP and decrease systemic platinum (Pt) exposure) was evaluated using a population pharmacokinetic analysis.

Methods:

Data from 55 patients treated with cisplatin-based IP perioperative chemotherapy with (n=26) or without (n=29) epinephrine were analysed using NONMEM.

Results:

Epinephrine halves clearance between peritoneum and serum (IPCL) and increases the Pt central volume of distribution, IP exposure and penetration in tissue. IPCL has a better predictive value than any other parameter with respect to renal toxicity.

Conclusion:

This confirms that IPCL could be useful in assessing renal toxicity. As IPCL is also linked to tissue penetration and IP exposure, it may be proposed as biomarker. In addition to a Bayesian estimation, we propose a single-sample calculation-way to assess it. Prospective studies are needed to validate IPCL as a biomarker in this context.

Meropenem in the treatment of complicated skin and soft tissue infections

Meropenem is a broad-spectrum carbapenem antibiotic with excellent activity against many pathogens associated with complicated skin and soft tissue infections (cSSTIs). At least three studies have shown meropenem to have good clinical efficacy and to be well tolerated in the treatment of cSSTIs. Two open-label studies compared meropenem 500 mg every 8 hours (total evaluable n=146) with imipenem/cilastatin 500mg every 6 hours (n=147). Clinical efficacy rates in evaluable patients 7–14 days after end of treatment were similar, 92% and 100% in meropenem-treated groups versus 89% and 100% in groups receiving imipenem/cilastatin. An additional prospective, randomized, double-blind study evaluated meropenem 500mg every 8 hours (261 evaluable patients) versus imipenem/cilastatin 500 mg every 8 hours (287 patients). Clinical efficacy rates of meropenem and imipenem/cilastatin 7–28 days after end of treatment were 86.2% and 82.9%, respectively. Meropenem was well tolerated in all studies. Carbapenems are currently recommended as appropriate for initial treatment of certain cSSTIs such as those likely to involve mixed and/or multidrug-resistant pathogens. Meropenem is an effective and safe alternative for monotherapy when used for appropriate types of cSSTIs. Higher doses (ie, 1 g every 8 hours) should be considered for treatment of cSSTIs in higher-risk patients where Pseudomonas aeruginosa is a suspected or documented pathogen.

Pharmacokinetics of ciprofloxacin and its penetration into bronchial secretions of mechanically ventilated patients with chronic obstructive pulmonary disease

We evaluated the pharmacokinetic profile of ciprofloxacin and its penetration into bronchial secretions of critically ill patients with chronic obstructive pulmonary disease (COPD). Twenty-five mechanically ventilated patients with severe COPD who were suffering from an acute, infectious exacerbation were included in this prospective, open-label study. All subjects received a 1-hour intravenous infusion of 400 mg ciprofloxacin every 8 h. Serial blood and bronchial secretion samples were obtained at steady state, and concentrations were determined using high-performance liquid chromatography. The pharmacodynamic parameters that are associated with the efficacy of fluoroquinolones against Gram-negative pathogens were also calculated. The mean peak (maximum) concentration (C(max)) and trough (minimum) concentration in plasma were 5.37 ± 1.57 and 1 ± 0.53 mg/liter, respectively. Mean values for volume of distribution, clearance, half-life, and area under the curve from 0 to 24 h (AUC(0-24)) were 169.87 ± 84.11 liters, 26.96 ± 8.86 liters/h, 5.35 ± 2.21 h, and 47.41 ± 17.02 mg · h/liter, respectively. In bronchial secretions, a mean C(max) of 3.08 ± 1.21 mg/liter was achieved in 3.12 ± 1.01 h, and the penetration ratio was 1.16 ± 0.59. The target of AUC(0-24)/MIC of ≥125 was attained in all patients, in the majority of them (76%), and in none at MICs of 0.125, 0.25, and 1 μg/ml, respectively. Slightly better results were obtained for the ratio C(max)/MIC of ≥10. In conclusion, ciprofloxacin demonstrates excellent penetration into bronchial secretions. There is wide interindividual variability in its pharmacokinetic parameters in critically ill COPD patients and inadequate pharmacodynamic exposure against bacteria with MICs of ≥0.5 μg/ml.

Optimizing ciprofloxacin dosing in intensive care unit patients through the use of population pharmacokinetic-pharmacodynamic analysis and Monte Carlo simulations

OBJECTIVES

To explore different ciprofloxacin dosage regimens for the treatment of intensive care unit (ICU) patients with respect to clinical outcome and the development of bacterial resistance for the major Gram-negative pathogens.

METHODS

A population pharmacokinetic model was first developed on ciprofloxacin serum concentrations obtained in 102 ICU patients. Then, based on this model, pharmacokinetic-pharmacodynamic Monte Carlo simulations (MCSs) were carried out to explore the appropriateness of different ciprofloxacin dosage regimens in ICU patients. The defined targets were free AUC(24)/MIC ≥90 h (as a predictor of clinical outcome) and T(MSW) ≤20% (as a predictor of selecting resistance), where T(MSW) is the time spent within the mutant selection window over 24 h. Two simulation trials were conducted: Trial 1 took into account the whole MIC distribution for each causative pathogen in line with empirical antibiotherapy; Trial 2 used MIC breakpoints given by the Antibiogram Committee of the French Microbiology Society in order to treat the 'worst-case' scenario.

RESULTS

Trial 1 showed that for Pseudomonas aeruginosa and Acinetobacter baumannii, the common dosage regimens of 400 mg twice or three times a day did not achieve the desired target attainment rates (TARs) with respect to T(MSW), while suboptimal TARs were found for AUC(24)/MIC. Trial 2 showed that ≤ 18% of patients reached the target of T(MSW) ≤ 20% for MIC breakpoints of 0.5 and 1 mg/L, regardless of the administered dose.

CONCLUSIONS

Based on the mutant selection window concept, our simulations truly question the use of ciprofloxacin for the treatment of P. aeruginosa and A. baumannii infections in ICU patients due to the potential for developing resistance.

Pharmacodynamic profiling of intravenous antibiotics against prevalent Gram-negative organisms across the globe: the PASSPORT Program-Asia-Pacific Region

Due to escalating antimicrobial resistance amongst Gram-negative organisms, the choice of effective empirical antimicrobial regimens has become challenging. Monte Carlo simulations were conducted for conventional and prolonged infusion regimens of doripenem, imipenem and meropenem using pharmacokinetic data from adult patients with conserved renal function. Minimum inhibitory concentration data against Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii were incorporated from the COMPACT surveillance programme in the Asia-Pacific region of the world. The cumulative fraction of response (CFR) was determined for each regimen against each bacterial population. All simulated carbapenem regimens achieved an optimal CFR against E. coli and K. pneumoniae (94.5-100% CFR). Against P. aeruginosa, doripenem achieved 78.7-92.6% CFR, imipenem achieved 60.4-79.0% CFR and meropenem achieved 73.0-85.1% CFR. The only dosing regimen to achieve ≥ 90% CFR against P. aeruginosa was doripenem 1000 mg and 2000 mg every 8 h (4-h infusion). Carbapenem CFRs against A. baumannii were much lower (29.2-54.4% CFR). CFRs for non-fermenting isolates were ca. 10% lower for isolates collected in the Intensive Care Unit. Carbapenem resistance amongst Enterobacteriaceae remains low in the Asia-Pacific region and thus standard carbapenem dosing regimens had a high likelihood of achieving pharmacodynamic exposures. However, larger doses combined with prolonged infusion will be required to increase the CFR for these carbapenems against resistant non-fermenting Gram-negatives that are common in these countries. The safety and efficacy of these high dosing regimens will need to be confirmed in the clinical setting.

Pharmacokinetic-pharmacodynamic profiling of four antimicrobials against gram-negative bacteria collected from Shenyang, China

Background

To examine common antimicrobial regimens used in eradicating certain nosocomial Gram-negative pathogens and determine which ones are likely to be the most suitable as empirical choices in Shenyang, China.

Methods

A 5000-subject Monte Carlo simulation was conducted to determine the cumulative fraction of response (CFR) for meropenem, imipenem, cefepime, piperacillin/tazobactam and levofloxacin against Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Acinetobacter baumannii and Pseudomonas aeruginosa collected in 2006 and 2007 from Shenyang.

Results

Meropenem and imipenem had the highest CFRs against the Enterobacteriaceae (97%-100%), followed by cefepime. No antibiotic simulated regimen achieved optimal CFR against P. aeruginosa and A. baumannii. Piperacillin/tazobactam dosed at 4.5 g q8h achieved the lowest CFR against all bacteria.

Conclusions

This study suggests that the carbapenems provide the greatest likelihood of clinical success for the Enterobacteriaceae, and combination therapy might be needed when choosing empirical therapy, especially when A. baumannii or P. aeruginosa are suspected.

Prospective monitoring of cefepime in intensive care unit adult patients

Introduction

Cefepime has been associated with a greater risk of mortality than other beta-lactams in patients treated for severe sepsis. Hypotheses for this failure include possible hidden side-effects (for example, neurological) or inappropriate pharmacokinetic/pharmacodynamic (PK/PD) parameters for bacteria with cefepime minimal inhibitory concentrations (MIC) at the highest limits of susceptibility (8 mg/l) or intermediate-resistance (16 mg/l) for pathogens such as Enterobacteriaceae, Pseudomonas aeruginosa and Staphylococcus aureus. We examined these issues in a prospective non-interventional study of 21 consecutive intensive care unit (ICU) adult patients treated with cefepime for nosocomial pneumonia.

Methods

Patients (median age 55.1 years, range 21.8 to 81.2) received intravenous cefepime at 2 g every 12 hours for creatinine clearance (CL_Cr) ≥ 50 ml/min, and 2 g every 24 hours or 36 hours for CL_Cr < 50 ml/minute. Cefepime plasma concentrations were determined at several time-points before and after drug administration by high-pressure liquid chromatography. PK/PD parameters were computed by standard non-compartmental analysis.

Results

Seventeen first-doses and 11 steady states (that is, four to six days after the first dose) were measured. Plasma levels varied greatly between individuals, from two- to three-fold at peak-concentrations to up to 40-fold at trough-concentrations. Nineteen out of 21 (90%) patients had PK/PD parameters comparable to literature values. Twenty-one of 21 (100%) patients had appropriate duration of cefepime concentrations above the MIC (T_>MIC ≥ 50%) for the pathogens recovered in this study (MIC ≤ 4 mg/l), but only 45 to 65% of them had appropriate coverage for potential pathogens with cefepime MIC ≥ 8 mg/l. Moreover, 2/21 (10%) patients with renal impairment (CL_Cr < 30 ml/minute) demonstrated accumulation of cefepime in the plasma (trough concentrations of 20 to 30 mg/l) in spite of dosage adjustment. Both had symptoms compatible with non-convulsive epilepsy (confusion and muscle jerks) that were not attributed to cefepime-toxicity until plasma levels were disclosed to the caretakers and symptoms resolved promptly after drug arrest.

Conclusions

These empirical results confirm the suspected risks of hidden side-effects and inappropriate PK/PD parameters (for pathogens with upper-limit MICs) in a population of ICU adult patients. Moreover, it identifies a safety and efficacy window for cefepime doses of 2 g every 12 hours in patients with a CL_Cr ≥ 50 ml/minute infected by pathogens with cefepime MICs ≤ 4 mg/l. On the other hand, prompt monitoring of cefepime plasma levels should be considered in case of lower CL_Cr or greater MICs.

Summary trends for the Meropenem Yearly Susceptibility Test Information Collection Program: a 10-year experience in the United States (1999-2008)

The Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program was a global, longitudinal antimicrobial resistance surveillance network of more than 100 medical centers worldwide monitoring the susceptibility of meropenem and selected other broad-spectrum comparator agents. In 1999, and from 2000 through 2008, a total of 10 or 15 United States (USA) medical centers each forwarded 200 nonduplicate clinical isolates from serious infections to a central processing laboratory. Over the 10-year period of this surveillance program, the activity of meropenem and an average of 11 other antimicrobial agents were assessed against a total of 27 289 bacterial isolates using Clinical and Laboratory Standards Institute reference methods. Meropenem consistently demonstrated low resistance rates against Enterobacteriaceae species isolates through 2008 and did not exhibit a widespread change in resistance rates over the monitored interval. In fact, the incidence of emerging carbapenemase-producing (KPC-type) Klebsiella spp. showed a decline in 2008 compared to the steeply increasing rates observed from 2004 to 2007. Moreover, the KPC serine carbapenemases have spread to other Enterobacteriaceae species monitored by the MYSTIC Program. Greatest increases in antimicrobial resistance rates were observed for the fluoroquinolones (ciprofloxacin, levofloxacin) among all species monitored by the MYSTIC Program. Current susceptibility rates for meropenem when tested against prevalent pathogens were Pseudomonas aeruginosa (439 strains, 85.4% susceptible), Enterobacteriaceae (1537 strains, 97.3% susceptible), methicillin-susceptible staphylococci (460 strains, 100.0% susceptible), Streptococcus pneumoniae (125 strains, 80.2% at meningitis susceptibility breakpoints), other streptococci (159 strains, 90.0-100.0% susceptible), and Acinetobacter spp. (127 strains, 45.7% susceptible), the widest spectrum among beta-lactams tested in 2008 and throughout the last decade. Continued local surveillance of broad-spectrum agents following the completion of the MYSTIC Program (USA) appears critical to detect emerging resistances among pathogens causing the most serious infections requiring carbapenem agents.

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.

Cefepime: a reappraisal in an era of increasing antimicrobial resistance

Cefepime is a 'fourth-generation' cephalosporin with an in vitro extended-spectrum of activity against Gram-negative and Gram-positive pathogens. Cefepime is approved for the treatment of moderate-to-severe infections, such as pneumonia, uncomplicated and complicated urinary tract infections, skin and soft-tissue infections, intra-abdominal infections and febrile neutropenia. In this article, we provide a critical review of pharmacodynamics, clinical management, pharmacokinetics, metabolism, pharmacodynamic target analyses, clinical efficacy, safety and tolerability of cefepime after more than a decade of clinical use.

Meropenem: a review of its use in the treatment of serious bacterial infections

Meropenem (Merrem, Meronem) is a broad-spectrum antibacterial agent of the carbapenem family, indicated as empirical therapy prior to the identification of causative organisms, or for disease caused by single or multiple susceptible bacteria in both adults and children with a broad range of serious infections. Meropenem is approved for use in complicated intra-abdominal infection (cIAI), complicated skin and skin structure infection (cSSSI) and bacterial meningitis (in paediatric patients aged > or = 3 months) in the US, and in most other countries for nosocomial pneumonia, cIAI, septicaemia, febrile neutropenia, cSSSI, bacterial meningitis, complicated urinary tract infection (UTI), obstetric and gynaecological infections, in cystic fibrosis patients with pulmonary exacerbations, and for the treatment of severe community-acquired pneumonia (CAP). Meropenem has a broad spectrum of in vitro activity against Gram-positive and Gram-negative pathogens, including extended-spectrum beta-lactamase (ESBL)- and AmpC-producing Enterobacteriaceae. It has similar efficacy to comparator antibacterial agents, including: imipenem/cilastatin in cIAI, cSSSI, febrile neutropenia, complicated UTI, obstetric or gynaecological infections and severe CAP; clindamycin plus tobramycin or gentamicin in cIAI or obstetric/gynaecological infections; cefotaxime plus metronidazole in cIAI; cefepime and ceftazidime plus amikacin in septicaemia or febrile neutropenia; and ceftazidime, clarithromycin plus ceftriaxone or amikacin in severe CAP. Meropenem has also shown similar efficacy to cefotaxime in paediatric and adult patients with bacterial meningitis, and to ceftazidime when both agents were administered with or without tobramycin in patients with cystic fibrosis experiencing acute pulmonary exacerbations. Meropenem showed greater efficacy than ceftazidime or piperacillin/tazobactam in febrile neutropenia, and greater efficacy than ceftazidime plus amikacin or tobramycin in patients with nosocomial pneumonia. Meropenem is well tolerated and has the advantage of being suitable for administration as an intravenous bolus or infusion. Its low propensity for inducing seizures means that it is suitable for treating bacterial meningitis and is the only carbapenem approved in this indication. Thus, meropenem continues to be an important option for the empirical treatment of serious bacterial infections in hospitalized patients.

Ciprofloxacin use in critically ill patients: pharmacokinetic and pharmacodynamic approaches

The objective of this study was to evaluate the properties of ciprofloxacin in intensive care patients using a population approach. Seventy patients received ciprofloxacin. On Day 1, three to eight blood samples were taken over a 12-h period. Peak drug concentration (Cmax) and 24-h area under the concentration-time curve (AUC) were compared with the French breakpoint defining antibiotic susceptibility. A population pharmacokinetic modelling approach was then carried out. A two-compartment open model with a proportional error model best fitted the data. A relationship between the elimination constant rate and the Cockcroft creatinine clearance was found. Ciprofloxacin clearance was 13.6+/-5.8L/h, the volume of distribution was 62.0+/-10.7 L and the ciprofloxacin half-life was 3.7+/-1.8h. When the minimum inhibitory concentration (MIC) was equal to 1mg/L the inhibitory ratio (IR) was > or = 8 in only 10.8% of cases, and the AUC/MIC ratio (AUIC) was 42.0+/-36. In conclusion, this study highlights that the Cockcroft clearance significantly influences ciprofloxacin elimination. Target plasma concentrations for ciprofloxacin, the IR and AUIC were rarely reached with a standard dosing regimen. In critically ill patients, the observed pharmacokinetic variability is mainly responsible for the overly frequent low concentrations of ciprofloxacin, emphasising the need for therapeutic monitoring.

Antimicrobial breakpoints for gram-negative aerobic bacteria based on pharmacokinetic-pharmacodynamic models with Monte Carlo simulation

OBJECTIVES

This study describes a comprehensive programme designed to develop pharmacokinetic-pharmacodynamic (PK-PD) breakpoints for numerous antimicrobial classes against key gram-negative aerobic bacteria.

METHODS

A 10,000 subject Monte Carlo simulation was constructed for 13 antimicrobials (21 dosing regimens). Published pharmacokinetic data and protein binding were varied according to log-normal and uniform distributions. MICs were fixed at single values from 0.03 to 64 mg/L. The PK-PD susceptible breakpoint was defined as the MIC at which the probability of target attainment was > or = 90%. PK-PD, CLSI and European Committee on Antimicrobial Susceptibility Testing breakpoints were applied to MICs from the 2005 worldwide Meropenem Yearly Susceptibility Test Information Collection database to evaluate the impact of breakpoint discrepancies.

RESULTS

PK-PD breakpoints were within one dilution of the CLSI and European breakpoints for all antimicrobials tested--with a few exceptions. When discrepancies were noted, the PK-PD breakpoint was lower than the CLSI breakpoint [ceftriaxone (0.5 versus 8 mg/L), ertapenem (0.25 versus 2 mg/L), ciprofloxacin (0.125 versus 1 mg/L) and levofloxacin (0.25-0.5 versus 2 mg/L)] and higher than the European breakpoint [ceftazidime (4-8 versus 1 mg/L), aztreonam (4-8 versus 1 mg/L), although ciprofloxacin was an exception to this pattern (0.125 versus 0.5-1 mg/L)]. For Enterobacteriaceae, breakpoint discrepancies resulted in modest (< or = 10%) differences in the percentages susceptible. In contrast, large (> 15%) discrepancies were noted for Pseudomonas aeruginosa and Acinetobacter baumannii.

CONCLUSIONS

Breakpoint agreement exists for imipenem, meropenem and the aminoglycosides. In contrast, discrepancies exist for piperacillin/tazobactam, cephalosporins, ertapenem, aztreonam and the fluoroquinolones. These discrepancies are most pronounced for P. aeruginosa and A. baumannii.

Pharmacodynamic comparison of linezolid, teicoplanin and vancomycin against clinical isolates of Staphylococcus aureus and coagulase-negative staphylococci collected from hospitals in Brazil

Pharmacodynamic exposures, measured as the ratio of steady-state total drug area under the curve to MIC (AUC/MIC), were modelled using a 5000-patient Monte-Carlo simulation against 119 non-duplicate clinical isolates of Staphylococcus aureus and 82 coagulase-negative staphylococci (CNS) collected from hospitals in Brazil between 2003 and 2005. Pharmacodynamic targets included an AUC/MIC >82.9 for linezolid and >345 for teicoplanin and vancomycin, as well as a free drug AUC/MIC >180 for vancomycin. The cumulative fractions of response (CFRs) against all S. aureus isolates were 96.0%, 30.1%, 71.6%, 48.0% and 65.1% for linezolid 600 mg every 12 h, teicoplanin 400 mg every 24 h and 800 mg every 24 h, and vancomycin 1000 mg every 12 h and every 8 h, respectively. Using a free drug target for vancomycin improved the CFR to 94.6% for the high-dose regimen, but did not substantially alter results for the lower dose. CFRs against all CNS isolates were 97.8%, 13.4%, 34.6%, 10.9% and 31.3%, respectively, for the same antibiotic regimens. The CFR was reduced for all compounds among the methicillin-resistant isolates, except for linezolid against methicillin-resistant CNS. Sensitivity analyses did not alter the final order of pharmacodynamic potency against these isolates. Although higher doses of vancomycin and teicoplanin increased the CFR, the likelihood of achieving bactericidal targets was still lower than with linezolid. The results for the high-dose vancomycin regimen were highly dependent on the pharmacodynamic target utilised. These data suggest that linezolid has a greater probability of attaining its requisite pharmacodynamic target than teicoplanin and vancomycin against these staphylococci.

Empiric therapy for secondary peritonitis: a pharmacodynamic analysis of cefepime, ceftazidime, ceftriaxone, imipenem, levofloxacin, piperacillin/tazobactam, and tigecycline using Monte Carlo simulation

BACKGROUND

Inappropriate antibiotic therapy (ie, the selection of an empiric agent without activity against the responsible pathogen) of secondary peritonitis may result in poor patient outcomes. The selection of an appropriate agent can be challenging because of the emerging resistance of target organisms to commonly prescribed antibiotics.

OBJECTIVE

The aim of this study was to perform a pharmacodynamic analysis, using recent global surveillance data, of commonly prescribed antibiotic agents and a newer agent, tigecycline, indicated in 2005 for the treatment of complicated intra-abdominal infections, to determine their probability for achieving microbiologic success against aerobic bacteria associated with secondary peritonitis.

METHODS

A 2-compartment model was constructed using pharmacokinetic data from critically ill patients and global surveillance data on MIC distributions for microorganisms encountered in secondary peritonitis. A Monte Carlo simulation of the modeled data was performed to determine drug-appropriate pharmacodynamic end points, including free-drug time above the MIC, steady-state concentration above the MIC, and AUC/MIC ratios. A cumulative fraction of response (CFR) against aerobic bacteria involved in secondary peritonitis was calculated for cefepime, ceftazidime, ceftriaxone, imipenem, levofloxacin, pip eracillin/tazobactam, and tigecycline. A CFR > or =90% was considered microbiologic success. The following treatment regimens, administered as 30-minute N infusions, were examined: cefepime 1 and 2 g q12h, ceftazidime 1 and 2 g q8h, ceftriaxone 1 and 2 g q24h, imipenem 500 mg q6h, levofloxacin 750 mg q24h, pip eracillin/tazobactam 3.375 g q6h, and tigecycline 50 mg q12h, after a loading dose of 100 mg.

RESULTS

A CFR > or =90% against nonenterococcal bacteria was predicted for imipenem 500 mg q6h (96.8%), cefepime 2 and 1 g q12h (95.3% and 92.4%, respectively), ceftazidime 2 g q8h (94.2%), and piperacillin/tazobactam 3.375 g q6h (91.2%). A CFR of 84.5% was predicted for tigecycline 50 mg q12h. Ceftriaxone and levofloxacin were predicted to have a CFR <80%. When enterococci were included in the model, the predicted CFRs for imipenem, piperacillin/tazobactam, and tigecycline were 93.4%, 88.4%, and 86.7%, respectively.

CONCLUSIONS

: MIC distribution and pathogen prevalence strongly influence the likelihood of microbiological success in secondary peritonitis; therefore, decisions regarding empiric therapy should consider local epidemiology. Using current global data, the following regimens are adequate choices if Enterococcus is not targeted: Combination therapy (with metronidazole) using cefepime 1 g or 2 g q12h, or ceftazidime 2 g q8h; or monotherapy with imipenem 500 mg q6h or piperacillin-tazobactam 3.375 g q6h. When Enterococcus is included in the epidemiologic mix, imipenem, piperacillin/tazobactam, and tigecycline all appear to be viable monotherapeutic choices.

Systematic comparison of the population pharmacokinetics and pharmacodynamics of piperacillin in cystic fibrosis patients and healthy volunteers

Respiratory tract infections cause 90% of premature mortality in patients with cystic fibrosis (CF). Treatment of Pseudomonas aeruginosa infection is often very problematic. Piperacillin-tazobactam has good activity against P. aeruginosa, but its pharmacokinetics (PK) in CF patients has not been compared to the PK in healthy volunteers in a controlled clinical study. Therefore, we compared the population PK and pharmacodynamics (PD) of piperacillin between CF patients and healthy volunteers. We studied 8 adult (median age, 20 years) CF patients (average total body weight [WT], 43.1 +/- 7.8 kg) and 26 healthy volunteers (WT, 71.1 +/- 11.8 kg) who each received 4 g piperacillin as a 5-min intravenous infusion. We determined piperacillin levels by high-performance liquid chromatography, and we used NONMEM for population PK and Monte Carlo simulation. We used a target time of nonprotein-bound concentration above the MIC of 50%, which represents near-maximal bacterial killing. Unscaled total clearance was 25% lower, and the volume of distribution was 31% lower in CF patients. Allometric scaling by lean body mass reduced the unexplained (random) between-subject variability in clearance by 26% compared to the variability of linear scaling by WT. A standard dosage regimen of 3 g/70 kg body WT every 4 h as a 30-min infusion (daily dose, 18 g) achieved a robust (> or =90%) probability-of-target attainment (PTA) for MICs of < or =12 mg/liter in CF patients and < or =16 mg/liter in healthy volunteers. Alternative modes of administration allowed a marked dose reduction to 9 g daily. Prolonged (4-h) infusions of 3 g/70 kg WT every 8 h and continuous infusion (daily dose, 9 g), achieved a robust PTA for MICs of < or =16 mg/liter in both groups. Piperacillin achieved PTA expectation values of 64% and 89% against P. aeruginosa infection in CF patients, based on susceptibility data from two German CF clinics.

Microbiology and Principles of Antimicrobial Therapy for Head and Neck Infections

The principles of antimicrobial management for head and neck infections include establishing an accurate clinical and microbiologic diagnosis and treating the patient initially with an empiric antimicrobial regimen based on predicted likelihood of success and reduced potential for resistance. Subsequent adjustments may be required based on clinical response and available culture results. This article summarizes the aerobic and anaerobic microbiology of selected acute and chronic infections of the head and neck and the approaches to antimicrobial therapy.

Evaluating Empiric Treatment Options for Secondary Peritonitis Using Pharmacodynamic Profiling

BACKGROUND

Selecting an appropriate agent for empiric antibiotic therapy for secondary peritonitis is challenging. The pathogens responsible, aerobic gram-negative bacilli in particular, are becoming more resistant to antibiotics. The purpose of this study was to predict the ability of common antimicrobial regimens to achieve optimal pharmacodynamic exposure against aerobic bacteria implicated in secondary peritonitis, while considering current national resistance trends.

METHODS

Monte Carlo simulation was used to model pharmacodynamic endpoints and compare the cumulative fraction of response (CFR) for imipenem-cilastatin, meropenem, ertapenem, piperacillin/tazobactam, ceftazidime, ceftriaxone, ciprofloxacin, and levofloxacin against isolates of species associated with secondary peritonitis. Minimum inhibitory concentration (MIC) distributions for isolates collected in North America were obtained from the 2004 MYSTIC database. Pharmacokinetic parameters were derived from the literature; the endpoints evaluated included free drug time above the MIC (fT(>MIC)) and the area under the concentration-time curve to MIC ratio (AUC:MIC).

RESULTS

The simulation predicted that several compounds would have a superior probability of providing appropriate coverage of aerobic bacteria: Imipenem-cilastatin (98.6% CFR at 1 g q8h), meropenem (98.2% CFR at 1 g q8h), ertapenem (91.7% CFR at 1 g q24h), piperacillin/ tazobactam (93.7% CFR at 3.375 g q6h), ceftazidime (91.1% CFR at 2 g q8h), and cefepime (92.9% CFR at 1 g q12h and 95.8% CFR at 2 g q12h). Ceftriaxone, ciprofloxacin, and levofloxacin exhibited CFRs < 82%.

CONCLUSIONS

Considering contemporary susceptibility data for aerobic bacteria, monotherapy with any of the three carbapenems or piperacillin/tazobactam 3.375 g q6h would provide optimal exposure for the pathogens commonly encountered in secondary peritonitis. Cefepime (in combination with metronidazole to provide anti-anaerobic coverage) also would be an acceptable choice, as would ceftazidime given at 2 g q8h (again in combination with metronidazole). Despite the popularity of combination therapy based on ciprofloxacin, levofloxacin, or ceftriaxone with metronidazole, these choices appear to be inferior to the other options because of emerging antibiotic resistance, particularly in E. coli.

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.

Optimising antibiotic dosing regimens based on pharmacodynamic target attainment against Pseudomonas aeruginosa collected in Hungarian hospitals

Owing to increasing resistance rates in Europe, pharmacodynamic analyses were proposed to determine optimal empirical antibiotic therapy against Pseudomonas aeruginosa isolated in Hungary. Minimum inhibitory concentrations for 180 non-duplicate P. aeruginosa collected from 14 hospitals in Hungary were determined by Etest methodology. A 5000-subject Monte Carlo simulation was performed to calculate the bactericidal cumulative fraction of response (CFR) for standard dosing regimens of cefepime, ceftazidime, ciprofloxacin, imipenem, meropenem and piperacillin/tazobactam. In the case of poor CFR, alternative dosage regimens were simulated for selected agents by increasing the infusion time, dose and frequency. Owing to high resistance rates in Hungary, no regimen achieved >90% CFR. CFRs for standard dosing regimens were: meropenem 1g every 8h (q8h), 77.1%; ceftazidime 2g q8h, 75.3%; imipenem 0.5 g every 6h (q6h), 71.7%; and piperacillin/tazobactam 4.5 g and 3.375 g q6h, 72.4% and 71.0%, respectively. Ciprofloxacin achieved significantly lower bactericidal CFRs than any beta-lactam. Prolonged infusion regimens improved the CFR for cefepime, imipenem, meropenem and piperacillin/tazobactam. Overall, the highest CFR (88.1%) was achieved by a 3-h infusion of meropenem 2g q8h. Given the poor CFR predicted with standard dosage regimens against these isolates, it seems prudent to consider alternative dosage strategies such as increasing doses, frequencies or infusion times as well as combination therapy when empirically treating infections caused by P. aeruginosa in Hungary.