The OPTAMA programme: utilizing MYSTIC (2002) to predict critical pharmacodynamic target attainment against nosocomial pathogens in Europe

Evaluating omadacycline dosing regimens against drug-resistant pathogens including Staphylococcus aureus, Streptococcus pneumoniae and Haemophilus influenzae in adults: a pharmacokinetic/pharmacodynamic analysis using Monte Carlo simulation

The objective of this study was to evaluate the efficacy of various dosing regimens of omadacycline against main drug-resistant pathogens in the treatment of acute bacterial skin and skin structure infections (ABSSSI) and community-acquired bacterial pneumonia (CABP). Monte Carlo simulations were conducted using pharmacokinetic parameters and pharmacodynamic data to calculate cumulative fractions of response (CFRs) in terms of drug area under the concentration curve/minimum inhibition concentration targets.CFR ≥ 90% was considered optimal for a dosage regimen. CFR of any approved oral/intravenous regimen with loading-dose was ≥ 90% against methicillin-resistant Staphylococcus aureus (MRSA) for ABSSSI and penicillin-resistant Streptococcus pneumonia, tetracycline-resistant Streptococcus pneumonia, MRSA and β-lactamase positive Haemophilus influenzae for CABP. In conclusion, approved oral/intravenous loading and maintenance doses of omadacycline showed enough efficacy in the treatment of ABSSI and CABP caused by the main drug-resistant pathogens.

Assessment of micafungin dosage regimens against Candida spp. in pediatric patients undergoing hematopoietic stem cell transplantation: a pharmacokinetic/pharmacodynamic analysis using Monte Carlo simulation

The objective of this study was to evaluate the efficacy of various micafungin dosing regimens against Candida spp. in pediatric patients undergoing hematopoietic stem cell transplantation (HSCT). Monte Carlo simulations were conducted using pharmacokinetic (PK) parameters and pharmacodynamic (PD) data to determine the probabilities of target attainment and cumulative fractions of response in terms of area under the concentration curve/minimum inhibition concentration targets of micafungin. Current standard clinical micafungin dosing regimens of 1 and 2 mg/kg/day were appropriate for the prevention and treatment of Candida glabrata infection in pediatric patients undergoing HSCT, respectively. Moreover, the high-dose prophylactic dosage (2 mg/kg/day) and therapeutic dosage (4 mg/kg/day) should be the preferred option to optimize efficacy against Candida albicans. However, none of the simulated regimens was effective against Candida parapsilosis in pediatric HSCT patients. These PK/PD-based simulations rationalize and optimize the micafungin dosing regimens against Candida spp. in pediatric patients undergoing HSCT.

The recommended dosage regimen for caspofungin in patients with higher body weight or hypoalbuminaemia will result in low exposure: Five years of data based on a population pharmacokinetic model and Monte-Carlo simulations

Background: To develop a population pharmacokinetic (PPK) model for caspofungin, identify parameters influencing caspofungin pharmacokinetics, and assess the required probability of target attainment (PTA) and cumulative fraction of response (CFR) for various dosing regimens of caspofungin in all patients and intensive care unit (ICU)-subgroup patients. Method: The general PPK model was developed based on data sets from all patients (299 patients). A ICU-subgroup PPK model based on data sets from 136 patients was then analyzed. The effects of demographics, clinical data, laboratory data, and concomitant medications were tested. Monte-Carlo simulations (MCS) were used to evaluate the effectiveness of different caspofungin dosage regimens. Results: One-compartment model best described the data of all patients and ICU patients. Clearances (CL) were 0.32 L/h and 0.40 L/h and volumes of distribution (V) were 13.31 L and 10.20 L for the general and ICU-subgroup PPK models, respectively. In the general model, CL and V were significantly associated with albumin (ALB) concentration and body weight (WT). In the ICU-subgroup model, CL was associated with WT. The simulated exposure in ICU patients was lower than that in all patients (p < 0.05). MCS indicated that higher caspofungin maintenance doses of 70-150 mg may achieve target CFR of >90% for patients with higher WT (>70 kg) or with C. albicans or C. parapsilosis infections, and especially for ICU patients with hypoalbuminaemia. Conclusion: The PPK model and MCS presented in the study demonstrated that the recommended dosage regimen for caspofungin in patients with higher body weight or hypoalbuminaemia will result in low exposure.

Population pharmacokinetic model-guided optimization of intravenous voriconazole dosing regimens in critically ill patients with liver dysfunction

STUDY OBJECTIVES

This study aimed to establish a population pharmacokinetic (PPK) model of intravenous voriconazole (VRC) in critically ill patients with liver dysfunction and to explore the optimal dosing strategies in specific clinical scenarios for invasive fungal infections (IFIs) caused by common Aspergillus and Candida species.

DESIGN

Prospective pharmacokinetics study.

SETTING

The intensive care unit in a tertiary-care medical center.

PATIENTS

A total of 297 plasma VRC concentrations from 26 critically ill patients with liver dysfunction were included in the PPK analysis.

METHODS

Model-based simulations with therapeutic range of 2-6 mg/L as the plasma trough concentration (C_min ) target and the free area under the concentration-time curve from 0 to 24 h (ƒAUC₂₄ ) divided by the minimum inhibitory concentration (MIC) (ie, ƒAUC₂₄ /MIC) ≥25 as the effective target were performed to optimize VRC dosing regimens for Child-Pugh class A and B (CP-A/B) and Child-Pugh class C (CP-C) patients.

RESULTS

A two-compartment model with first-order elimination adequately described the data. Significant covariates in the final model were body weight on both central and peripheral distribution volume and Child-Pugh class on clearance. Intravenous VRC loading dose of 5 mg/kg every 12 h (q12h) for the first day was adequate for CP-A/B and CP-C patients to attain the C_min target at 24 h. The maintenance dose regimens of 100 mg q12h or 200 mg q24h for CP-A/B patients and 50 mg q12h or 100 mg q24h for CP-C patients could obtain the probability of effective target attainment of >90% at an MIC ≤0.5 mg/L and achieve the cumulative fraction of response of >90% against C. albicans, C. parapsilosis, C. glabrata, C. krusei, A. fumigatus, and A. flavus. Additionally, the daily VRC doses could be increased by 50 mg for CP-A/B and CP-C patients at an MIC of 1 mg/L, with plasma C_min monitored closely to avoid serious adverse events. It is recommended that an appropriate alternative antifungal agent or a combination therapy could be adopted when an MIC ≥2 mg/L is reported, or when the infection is caused by C. tropicalis but the MIC value is not available.

CONCLUSIONS

For critically ill patients with liver dysfunction, the loading dose of intravenous VRC should be reduced to 5 mg/kg q12h. Additionally, based on the types of fungal pathogens and their susceptibility to VRC, the adjusted maintenance dose regimens with lower doses or longer dosing intervals should be considered for CP-A/B and CP-C patients.

Pharmacokinetic/pharmacodynamic modelling to evaluate the efficacy of various dosing regimens of ceftazidime/avibactam in patients with pneumonia caused by Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae: a multicentre study in northern China

OBJECTIVES

The objective of this study was to evaluate the efficacy of different dosing regimens of ceftazidime/avibactam (CZA) in patients with Klebsiella pneumoniae carbapenemase-producing K. pneumoniae (KPC-Kp) pulmonary infections.

METHODS

A total of 70 KPC-Kp strains were isolated from sputum and bronchoalveolar lavage samples of patients with pulmonary infections in three hospitals in northern China from April 2015 to October 2015. Monte Carlo simulation (MCS) was performed using population pharmacokinetic parameters of CZA combined with the minimum inhibitory concentration (MIC) distributions gained from antimicrobial susceptibility testing to predict the efficacy of different dosing regimens. Various CZA dosing regimens were modelled using MCS.

RESULTS

The in vitro study showed potent activity of CZA against KPC-Kp strains with MIC_50/90 values of 1/2 mg/L, with a susceptibility rate of 95.7%. The values of cumulative fraction of response (CFR) for bactericidal (50%fT>5 × MIC) target were as follows: for patients with creatinine clearance (CL_Cr) >51 mL/min, the CFR was 96.01% for 2.5 g CZA every 12 h (q12h) and 97.14% for 2.5 g CZA every 8 h (q8h); and for patients with moderate renal impairment (CL_Cr >30 to ≤50 mL/min), the CFR was 95.75% for 1.25 g CZA q12h and 97.09% for 1.25 g CZA q8h.

CONCLUSION

This study indicated that the recommended dose of CZA can provide adequate pharmacodynamic exposure for treating KPC-Kp pneumonia.

Population pharmacokinetics and Monte Carlo simulation for dosage optimization of fosfomycin in the treatment of osteoarticular infections in patients without renal dysfunction

Background: Fosfomycin is gaining interest in the treatment of complex osteoarticular infections (OI) due to MDR pathogens.Objective: The aims were to conduct population pharmacokinetics of fosfomycin in a cohort of OI patients receiving 16g/daily by intermittent (II) or continuous infusion (CI), and to carry out Monte Carlo simulations for dosage optimization in the treatment of these infections.Methods: Patients underwent blood sampling on day 5 of therapy (2-3 serial samples). Population pharmacokinetics and Monte Carlo simulations were performed to define the probability of target attainment (PTA) of 70% T>MIC, and the cumulative fraction of response (CFR) against common OI pathogens with dosages of 8, 12, 16, and 20g/day administered by II, extended-infusion (EI) or CI.Results: Forty-eight patients were recruited. A two-compartment open model with infusion input and first-order elimination was developed. Estimated creatinine clearance (CL_CR) was included as covariate in the final model. Monte Carlo simulations showed that optimal PTAs and CFRs (≥90%) may be achieved in three different classes of renal function by administering a daily dosage of: 2g q6h by II against S. aureus, E. coli, ESBL-producing E. Coli and MRSA; 8g by CI against CoNS, K. pneumoniae and ESBL-producing K. pneumoniae; 12g by CI against P. aeruginosa, and 16g by CI against KPC-producing K. pneumoniae Conclusion: Our study provides a strong rationale for considering fosfomycin dosages of  8-16 g daily by CI in several clinical scenarios for OI patients. Feasibility of administration by CI in an elastomeric pump makes fosfomycin a candidate for OPAT programs.

Population pharmacokinetics of dalbavancin and dosing consideration for optimal treatment of adult patients with staphylococcal osteoarticular infections

Background: Dalbavancin is gaining interest in the treatment of complex osteoarticular (OA) infections.Objective: To conduct a population pharmacokinetic analysis of dalbavancin in a prospective cohort of adult patients with Gram-positive OA infections and to identify optimal dosing regimens for long term-treatment.Methods: Non-linear mixed-effects modelling was performed with Monolix. Monte Carlo simulations were performed with six dalbavancin regimens (1500mg at day 1; 1000mg at day 1 plus 500mg at day 8; 1500mg at day1 and 8; 1500mg at day1 and 8 plus 500, 1000 or 1500mg at day 36) to assess the PTA of three pharmacodynamic target of fAUC_24h/MIC against S. aureus (>27.1, 53.3 and 111.1). Cumulative fraction of response (CFR) was calculated against MIC distribution of both MRSA and MSSA as well. Desirable PTAs and CFRs were ≥90%.Results: Fifteen patients provided 120 plasma concentrations. Most (73.3%) had prosthetic joint infections. Clinical cure rate was 87%. A two-compartment model with linear elimination well described the data. No covariate was retained in the final model. Pharmacokinetic dalbavancin estimates were 0.106L/h for CL and 36.4L for V_ss The tested dosing regimens granted desirable CFRs against S. aureus at the most effective PK/PD target for a period ranging 3-to-9 weeks. Conclusion: Giving a two 1500mg dosing regimen of dalbavancin one week apart may ensure efficacy against both MSSA and MRSA up to 5 weeks in patients with OA infections. Clinical assessment at that time may allow for considering whether or not an additional dose should be administered for prolonging effective treatment.

Population Pharmacokinetics and Model-Based Dosing Optimization of Teicoplanin in Pediatric Patients

Objectives: The pharmacokinetics (PK) of teicoplanin differs in children compared with adults. Our aim was to determine the PK of teicoplanin in an Asian pediatric population and to optimize dosage regimens. Methods: This was a retrospective PK study and all the data were collected from hospitalized children. We developed a population PK model using sparse data, and Monte Carlo simulation was used to assess the ability of standard teicoplanin regimen and other different dosage regimens. The optimal dosing regimens were defined as achieving the target trough concentration (C _min) of 10 mg/L and pharmacokinetic/pharmacodynamic (PK/PD, [AUC₂₄/MIC]) of 125 for moderate infection. For severe infection, the optimal dosing regimens were defined as achieving the target 15 mg/L and AUC₂₄/MIC of 345. Results: 159 children were included and 1.5 samples/children on average were provided. Estimated clearance of teicoplanin was 0.694 L/h (0.784/L/h/70 kg) and volume of distribution was 1.39 L. Teicoplanin standard loading dose was adequate for moderate infection, while 13 mg/kg was needed for severer infection. With standard maintenance doses, both patients with moderate and severe infection failed to achieve the target C _min. 12 and 16 mg/kg/day were required to achieve a C _min ≥ 10 and 15 mg/L, respectively. However, standard maintenance dose was adequate to achieve AUC₂₄/MIC ≥ 125 for moderate infection, and 12 mg/kg/day was needed to achieve AUC₂₄/MIC ≥ 345 for severe infection. Lower weight and serum creatinine were associated with higher dose. Conclusion: Optimal doses based on the target C _min were higher than that based on the PK/PD target. To achieve the C _min and PK/PD targets simultaneously, a standard loading dose was adequate for moderate infection based on simulation, while dosing higher than standard doses were required in other situation. Further clinical studies with rich sampling from children is required to confirm our findings.

Long-Term Continuous Antimicrobial Resistance Surveillance Among Nosocomial Gram-Negative Bacilli in China from 2010 to 2018 (CMSS)

Purpose

The Chinese Meropenem Surveillance Study (CMSS) was conducted every 2 years from 2010 to 2018 to monitor the antimicrobial activity of commonly used antimicrobial agents against nosocomial gram-negative bacilli in China.

Methods

From 2010 to 2018, 6,537 gram-negative bacilli were collected from 14 teaching hospitals. The minimum inhibitory concentrations (MICs) of meropenem and other antimicrobial agents were determined using the agar dilution and broth microdilution methods.

Results

Continuous surveillance indicated that, except for Klebsiella pneumoniae, the susceptibility of Enterobacterales to carbapenems was relatively stable over time. Carbapenems had the highest activity against the tested isolates, with MIC₉₀ values (MIC for 90% of organisms) ranging from 0.032 mg/L to 8 mg/L. More than 90% of bacteria were susceptible to either meropenem or imipenem; more than 80% were susceptible to ertapenem. The prevalence of extended-spectrum beta-lactamase (ESBL)-producing E. coli, K. pneumoniae, and P. mirabilis each year was 50.4–64.3%, 18–41.2%, and 1.9–33.8%, respectively. The prevalence of carbapenem-resistant K. pneumoniae (CRKP) and carbapenem-resistant Acinetobacter baumannii (CRAB) continued to increase significantly over time, from 7.6% to 21.2% and 64.6% to 69.3%, respectively. The prevalence of CRKP was higher from urinary tract infections (25.4%) than from bloodstream infections (14.2%), intra-abdominal infections (14.5%), and respiratory infections (14.4%). In total, 129 CRKP isolates were evaluated by PCR; of these, 92 (71.3%) carried the bla_KPC-2 gene. Colistin maintained very high in vitro antimicrobial activity against P. aeruginosa and A. baumannii (more than 95% of isolates exhibited susceptibility at all timepoints).

Conclusion

The results indicate an increase in K. pneumoniae resistance to carbapenems over time, mainly owing to KPC-type carbapenemase production. A. baumannii was severely resistant to carbapenems in China. Ongoing MIC-based resistance surveillance, like CMSS, provides additional data for clinical anti-infective treatment.

Population pharmacokinetics of continuous-infusion ceftazidime in febrile neutropenic children undergoing HSCT: implications for target attainment for empirical treatment against Pseudomonas aeruginosa

OBJECTIVES

To conduct a population pharmacokinetic analysis of continuous-infusion ceftazidime in a retrospective cohort of paediatric HSCT patients who were empirically treated for febrile neutropenia (FN) and who underwent therapeutic drug monitoring of ceftazidime steady-state plasma concentrations (Css) for optimization of drug exposure.

METHODS

A non-parametric approach with Pmetrics was used for pharmacokinetic analysis and covariate evaluation. Monte Carlo simulations were performed to calculate the PTA of the pharmacodynamic determinant of efficacy (Css/MIC ≥4) against Pseudomonas aeruginosa with continuous-infusion ceftazidime dosages of 1-6 g daily. The Css safety threshold was arbitrarily placed at 100 mg/L and advisable dosages were used.

RESULTS

A total of 46 patients with 70 ceftazidime Css values were included. Estimated glomerular filtration rate (eGFR) and body surface area were the covariates associated with drug clearance. At the EUCAST clinical breakpoint of 8 mg/L, simulations showed that continuous-infusion ceftazidime dosages of 4-6 g daily attained optimal PTAs (>90%) across most of 16 different clinical scenarios based on four classes of eGFR (50-145, 145.1-200, 200.1-286 and 286.1-422 mL/min/1.73 m2) and body surface area (0.30-0.64, 0.65-0.88, 0.89-1.34 and 1.35-1.84 m2). In patients with body surface area 0.30-0.64 m2 and eGFR ≤200 mL/min/1.73 m2 the advisable dose of 3 g daily allowed only suboptimal PTAs (<75%). The cumulative fraction of response against MIC distribution of P. aeruginosa was >87%.

CONCLUSIONS

Continuous-infusion ceftazidime dosages ranging from 3 to 6 g daily according to different classes of eGFR and body surface area may allow optimized empirical treatment of P. aeruginosa infections in paediatric HSCT patients with FN.

Optimizing Antibiotic Treatment Strategies for Neonates and Children: Does Implementing Extended or Prolonged Infusion Provide any Advantage?

Optimizing the use of antibiotics has become mandatory, particularly for the pediatric population where limited options are currently available. Selecting the dosing strategy may improve overall outcomes and limit the further development of antimicrobial resistance. Time-dependent antibiotics optimize their free concentration above the minimal inhibitory concentration (MIC) when administered by continuous infusion, however evidences from literature are still insufficient to recommend its widespread adoption. The aim of this review is to assess the state-of-the-art of intermittent versus prolonged intravenous administration of antibiotics in children and neonates with bacterial infections. We identified and reviewed relevant literature by searching PubMed, from 1 January 1 2000 to 15 April 2020. We included studies comparing intermittent versus prolonged/continuous antibiotic infusion, among the pediatric population. Nine relevant articles were selected, including RCTs, prospective and retrospective studies focusing on different infusion strategies of vancomycin, piperacillin/tazobactam, ceftazidime, cefepime and meropenem in the pediatric population. Prolonged and continuous infusions of antibiotics showed a greater probability of target attainment as compared to intermittent infusion regimens, with generally good clinical outcomes and safety profiles, however its impact in terms on efficacy, feasibility and toxicity is still open, with few studies led on children and adult data not being fully extendable.

Population pharmacokinetics of fluconazole in liver transplantation: implications for target attainment for infections with Candida albicans and non-albicans spp

OBJECTIVES

The study aims to assess the population pharmacokinetics of fluconazole and the adequacy of current dosages and breakpoints against Candida albicans and non-albicans spp. in liver transplant (LT) patients.

PATIENTS AND METHODS

Patients initiated i.v. fluconazole within 1 month from liver transplantation (LTx) for prevention or treatment of Candida spp. infections. Multiple assessments of trough and peak plasma concentrations of fluconazole were undertaken in each patient by means of therapeutic drug monitoring. Monte Carlo simulations were performed to define the probability of target attainment (PTA) with a loading dose (LD) of 400, 600, and 800 mg at day 1, 7, 14, and 28 from LTx, followed by a maintenance dose (MD) of 100, 200, and 300 mg daily of the pharmacokinetic/pharmacodynamic target of AUC_24h/MIC ratio ≥ 55.2.

RESULTS

Nineteen patients were recruited. A two-compartment model with first-order intravenous input and first-order elimination was developed. Patient's age and time elapsed from LTx were the covariates included in the final model. At an MIC of 2 mg/L, a LD of 600 mg was required for optimal PTAs between days 1 and 20 from LTx, while 400 mg was sufficient from days 21 on. A MD of 200 mg was required for patients aged 40-49 years old, while a dose of 100 mg was sufficient for patients aged ≥ 50 years.

CONCLUSIONS

Fluconazole dosages of 100-200 mg daily may ensure optimal PTA against C. albicans, C. parapsilosis, and C. tropicalis. Higher dosages are required against C. glabrata. Estimated creatinine clearance is not a reliable predictor of fluconazole clearance in LT patients.

A strategy for designing voriconazole dosage regimens to prevent invasive pulmonary aspergillosis based on a cellular pharmacokinetics/pharmacodynamics model

Background

Invasive pulmonary aspergillosis (IPA) is a life-threatening disease in immunosuppressed patients. Voriconazole is commonly used to prevent and treat IPA in the clinic, but the optimal prophylactic antifungal regimen is unknown. The objective of this study was to clarify the mechanism underlying how voriconazole prevents IPA based on a target cellular pharmacokinetics/pharmacodynamics model, with the aim of identifying a way to design an optimal prophylactic antifungal regimen.

Methods

A nystatin assay was used to establish a target-cells model for A. fumigatus infection. An inhibitory effect sigmoid E_max model was developed to explore the cellular PK/PD breakpoint, and Monte Carlo simulation was used to design the prophylactic antifungal regimen.

Results

The intracellular activity of voriconazole in the target cells varied with its concentration, with the minimum inhibitory concentration (MIC) being an important determinant. For A. fumigatus strains AF293 and AF26, voriconazole decreased the intracellular inoculum by 0.79 and 0.84 lg cfu, respectively. The inhibitory effect sigmoid E_max model showed that 84.01% of the intracellular inoculum was suppressed by voriconazole within 24 h, and that a PK/PD value of 35.53 for the extracellular voriconazole concentration divided by MIC was associated with a 50% suppression of intracellular A. fumigatus. The Monte Carlo simulation results showed that the oral administration of at least 200 mg of voriconazole twice daily was yielded estimated the cumulative fraction of response value of 91.48%. Concentration of voriconazole in the pulmonary epithelial lining fluid and the plasma of > 17.77 and > 1.55 mg/L, respectively, would ensure the PK/PD > 35.53 for voriconazole against most isolates of A. fumigatus and may will be benefit to prevent IPA in clinical applications.

Conclusions

This study used a target cellular pharmacokinetics/pharmacodynamics model to reveal a potential mechanism underlying how voriconazole prevents IPA and has provided a method for designing voriconazole prophylactic antifungal regimen in immunosuppressed patients.

Pharmacokinetic/Pharmacodynamic Analysis of Isavuconazole Against Aspergillus spp. and Candida spp. in Healthy Subjects and Patients With Hepatic or Renal Impairment by Monte Carlo Simulation

The aim of this pharmacokinetic/pharmacodynamic (PK/PD) study is to evaluate the efficacy of various isavuconazole dosing regimens for healthy individuals and patients with hepatic or renal impairment against Aspergillus spp. and Candida spp. Monte Carlo simulations were conducted using pharmacokinetic (PK) parameters and pharmacodynamics (PD) data to determine the probabilities of target attainment and cumulative fractions of response in terms of area under the concentration curve/minimum inhibition concentration (AUC/MIC) targets of isavuconazole. A clinically recommended dosage regimen of isavuconazole (200 mg qd) obtained high cumulative fraction of response values of > 90% for all subjects against A. fumigatus, A. flavus, A. nidulans, A. terreus, A. versicolor, C. parapsilosis and C. tropicalis. For patients with mild or moderate hepatic impairment, the dosage should be halved only when treating invasive fungal infections caused by C. albicans, C. parapsilosis or C. tropicalis. However, dose adjustment is unlikely to be required in mild to severe renal impairment patients because all cumulative fraction of response values were similar to those of comparing with healthy subjects. Notably, all isavuconazole dosing regimens were not effective against C. glabrata and C. krusei in all subjects. These PK/PD-based simulations rationalize and optimize the dosage regimens of isavuconazole for healthy individuals and patients with hepatic or renal impairment against Aspergillus spp. and Candida spp.

Population Pharmacokinetics of High-Dose Continuous-Infusion Meropenem and Considerations for Use in the Treatment of Infections Due to KPC-Producing Klebsiella pneumoniae

We assessed the population pharmacokinetics of high-dose continuous-infusion (HDCI) meropenem in a cohort of patients with Klebsiella pneumoniae carbapenemase (KPC)-producing Klebsiella pneumoniae (KPC-Kp) infections. Monte Carlo simulations were used to define the permissible HDCI meropenem regimens that could be safely considered for the treatment of KPC-Kp infections due to meropenem-resistant strains. Permissible doses were arbitrarily defined as those associated with a ≤10% to 15% likelihood of meropenem steady-state concentrations (C_ss) of >100 mg/liter. Probabilities of target attainment (PTA) of four incremental pharmacodynamic determinants for meropenem efficacy (100% T_>1×MIC, 100% T_>2×MIC, 100% T_>3×MIC, and 100% T_>4×MIC, where "T_>MIC" represents the time during which the plasma concentration of this time-dependent antibacterial agent is maintained above the MIC for the pathogen) in relation to different classes of renal function were calculated. The cumulative fractions of response (CFR) for the permissible HDCI meropenem regimens were calculated against the MIC distribution of the KPC-Kp clinical isolates that were collected routinely at our University Hospital between 2013 and 2016 (n = 169). Ninety-seven meropenem C_ss were included in the analysis. The final model included creatinine clearance (CrCL) as a covariate and explained 94% of the population variability. Monte Carlo simulations based on licensed dosages of up to 6 g/day predicted an acceptable PTA (>80%) of 100% T_>1×MIC against KPC-Kp with a meropenem MIC of ≤32 mg/liter in patients with a CrCL level of <130 ml/min. Dosages of 8 g/day were needed for achieving the same target in patients with CrCL at levels of 130 to 200 ml/min. In dealing with pathogens with a meropenem MIC of 64 mg/liter, HDCI regimens using meropenem at higher than licensed levels should be considered. In these cases, real-time therapeutic drug monitoring could be a useful adjunct for optimized care. The predicted CFR were >75% in all of the classes of renal function.

Pharmacodynamically Guided Levofloxacin Dosing for Pediatric Community-Acquired Pneumonia

BACKGROUND.

Oral levofloxacin is recommended as a preferred treatment for infection with Streptococcus pneumoniae with a penicillin minimum inhibitory concentration (MIC) of ≥4 µg/mL and as an alternative for infection with S pneumoniae with a penicillin MIC of ≤2 µg/mL. To investigate the current dosing recommendations and create a pharmacodynamically guided regimen, a Monte Carlo simulation was performed.

METHODS.

The simulation included a previously published 1-compartment model, and incorporated a formula that takes into account age-appropriate weights for hospitalized patients. Three different dosing regimens, including community-acquired pneumonia guideline dosing, inhalational anthrax dosing, and a pharmacodynamically guided regimen, were assessed. The probability of target attainment was described as the proportion of patients who achieve an unbound-drug area under the concentration-time curve over 24 hours divided by the MIC above 33.7 µg/mL per hour. Microbiologic data from 2 stand-alone pediatric tertiary care centers were included.

RESULTS.

Guideline-recommended doses of levofloxacin seem to produce suboptimal exposure in patients aged 5-14 years for pneumococci with an MIC of 1 µg/mL. Anthrax dosing was suboptimal in patients aged <5 years and in those aged >15 years. The pharmacodynamically guided regimen maintained a probability of target attainment of >90% for all age groups without producing peak concentrations higher than those previously described. None of the regimens attained the pharmacodynamic targets for a levofloxacin MIC of 2 µg/mL.

CONCLUSIONS.

Current dosing recommendations were found to be suboptimal for specific age groups. A pharmacodynamically guided levofloxacin dosing regimen was determined, but it will need to be studied clinically for safety and tolerability.

Population Pharmacokinetics and Pharmacodynamics of Piperacillin/Tazobactam in Patients with Nosocomial Infections

OBJECTIVE

The study was to establish a population pharmacokinetic (PPK) model of piperacillin (PIP) and tazobactam (TAZ) that explain pharmacokinetic variability and to propose optimized dosage regimens in patients with nosocomial infections.

METHODS

In total, 310 PIP and 280 TAZ concentration-time points were collected at steady state over multiple dosing intervals from 50 patients who received PIP/TAZ infused within 30 min or over 3 h. Drug analysis was performed by high-performance liquid chromatography (HPLC). Nonlinear mixed effects modeling was employed to develop PPK model and 1000 Monte Carlo simulation was used to predict the probability of target attainment (PTA) with a target time of non-protein-bound concentration above MIC > 50 % of the dosing interval.

RESULTS

A model with one-compartment model had the best predictive performance for the PPK model. The population estimates of PIP were 13.8 L/h (31.1 %) for clearance (CL) and 21.7 L (38 %) for volume of distribution (V). The population estimates of TAZ were 9.3 L/h (29.1 %) for CL and 16 L (35.3 %) for V. Influence of creatinine clearance (CLcr) and body weight were identified as important covariates for PIP/TAZ CL and V, respectively. A 30-min infusion of 4 g every 6 h achieved robust (≥90 %) PTAs for MIC ≤ 16 mg/L. As an alternative mode of administration, a 3-h infusion of 4 g every 6 h achieved robust PTAs for Pseudomonas aeruginosa and Klebsiella pneumoniae.

CONCLUSIONS

Prolonged infusions achieved better PTAs compared with shorter infusions at similar daily doses. This benefit was most pronounced for MICs between 16 and 40 mg/L.

Pharmacokinetic/pharmacodynamic analysis of voriconazole against Candida spp. and Aspergillus spp. in children, adolescents and adults by Monte Carlo simulation

The objective of this study was to investigate the cumulative fraction of response of various voriconazole dosing regimens against six Candida and six Aspergillus spp. in immunocompromised children, immunocompromised adolescents, and adults. Using pharmacokinetic parameters and pharmacodynamic data, 5000-subject Monte Carlo simulations (MCSs) were conducted to evaluate the ability of simulated dosing strategies in terms of fAUC/MIC targets of voriconazole. According to the results of the MCSs, current voriconazole dosage regimens were all effective for children, adolescents and adults against Candida albicans, Candida parapsilosis and Candida orthopsilosis. For adults, dosing regimens of 4 mg/kg intravenous every 12 h (q12h) and 300 mg orally q12h were sufficient to treat fungal infections by six Candida spp. (C. albicans, C. parapsilosis, Candida tropicalis, Candida glabrata, Candida krusei and C. orthopsilosis) and five Aspergillus spp. (Aspergillus fumigatus, Aspergillus flavus, Aspergillus terreus, Aspergillus niger and Aspergillus nidulans). However, high doses should be recommended for children and adolescents in order to achieve better clinical efficacy against A. fumigatus and A. nidulans. The current voriconazole dosage regimens were all ineffective against A. niger for children and adolescents. All voriconazole dosage regimens were not optimal against Aspergillus versicolor. This is the first study to evaluate clinical therapy of various voriconazole dosing regimens against Candida and Aspergillus spp. infections in children, adolescents and adults using MCS. The pharmacokinetic/pharmacodynamic-based dosing strategy provided a theoretical rationale for identifying optimal voriconazole dosage regimens in children, adolescents and adults in order to maximise clinical response and minimise the probability of exposure-related toxicity.

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.

Changes in gram negative microorganisms' resistance pattern during 4 years period in a referral teaching hospital; a surveillance study

Background and purpose

Surveillance studies evaluating antimicrobial susceptibilities are of great value in preventing the spread of resistant pathogens by elucidating the trend of resistance in commonly used antibiotics and as a consequence providing information for prescribing the most appropriate agent. This study is a longitudinal antimicrobial resistance surveillance study designed to evaluate the trend in antimicrobial resistance to gram negative microorganisms from 2007 to 2010.

Method

During a four-year period (2007–2010) isolates derived from all patients admitted to infectious diseases ward of Imam Khomeini Hospital, the major referral center for infectious disease in Iran with the highest admission rates, were evaluated. Based on disk diffusion method and zone of inhibition size, the microorganism was regarded as to be sensitive, resistant or has intermediate susceptibility to the antimicrobial agents.

Results

The widest spread Gram-negative microorganism in all of isolates taken together in our study was E.coli (30%) followed by Stenotrophomonas maltophilia in 28.6% and Enterobacter spp. in 11.9%, respectively. The susceptibility to amikacin, imipenem, piperacillin/tazobactam, and nitrofurantoin was equal or above 50% for all microorganisms over four years. However, the susceptibility to ampicillin, ampicillin/sulbactam, cefotaxim, and ceftriaxone was less than 50% in derived isolates during the study period.

Conclusion

In conclusion, the finding of the present study revealed that resistance rate to common antimicrobial agents in Iran is growing and isolates were susceptible mostly to broad-spectrum antibiotics including imipenem and piperacillin/tazobactam.

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.

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.

Approaches to improving antibiotic management

New information is available to improve antibiotic outcomes in severe sepsis where increasing resistance and reducing novel compound development make reaching the right decisions ever more difficult and important.

Optimizing bactericidal exposure for beta-lactams using prolonged and continuous infusions in the pediatric population

BACKGROUND

Administration of beta-lactams via prolonged or continuous infusion has been utilized in adults to optimize drug exposure and clinical outcomes. As children exhibit increased drug clearance, this may further the benefit of prolonged or continuous infusions. This dosing approach was applied to several beta-lactams commonly utilized in children.

PROCEDURE

A variety of cefepime, ceftazidime, imipenem/cilastatin, meropenem, and piperacillin/tazobactam regimens using administration times of 0.5, 3, or 24 hr infusions were simulated in populations of 2- and 12-year-old children using Monte Carlo techniques. The probability of target attainment (PTA) was calculated for each dosing regimen. Minimum inhibitory concentration (MIC) frequencies for Pseudomonas aeruginosa were obtained for two pediatric acute care institutions in order to calculate cumulative fractions of response (CFR).

RESULTS

Standard 0.5 hr infusions resulted in poor PTA for most study agents at their susceptibility breakpoint, whereas 3 hr infusions markedly improved PTA for cefepime (79 to 100%), ceftazidime (80 to 100%), imipenem (41 to 91%), and meropenem (33 to 97%). Piperacillin/tazobactam could not achieve a PTA > 21% for any dosing regimen at its breakpoint, though large improvements were observed at lower MICs. Continuous infusion regimens resulted in similar PTA results to the same dose administered as 3 hr infusions. CFR values for all drugs at both institutions improved when 3 hr or continuous infusions were employed.

CONCLUSIONS

Prolonged and continuous infusion dosing strategies improved the likelihood of obtaining bactericidal targets for these beta-lactams in a simulated pediatric population. Based on these data, pediatric studies employing these strategies are warranted.

The use of carbapenems in the treatment of serious infections

Inadequate initial antimicrobial treatment in serious infections leads to increased mortality. Achieving adequate treatment is increasingly difficult because of the increasing prevalence of multidrug-resistant (MDR) pathogens. The carbapenems are potent, broad-spectrum antibiotics that have been shown to be safe and efficacious therapies in the treatment of serious infections. This review is intended to compare the 4 major members of the carbapenem class, which include imipenem, meropenem, ertapenem, and doripenem, with other widely used antimicrobial agents in the intensive care unit (ICU). The carbapenems are potent, broad-spectrum antibiotics that have been shown to be safe and efficacious therapies in the treatment of serious infections. They provide better gram-negative coverage than other beta-lactams and are stable against extended-spectrum beta-lactamases and AmpC beta-lactamases, making them effective in the treatment of many MDR bacteria. The newly approved carbapenem, doripenem, may help preserve the utility of the carbapenem class.

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.

Antibiotic resistance surveillance over a 4-year period (2000–2003) in Turkey: results of the MYSTIC Program

The Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program is a global study that provides antimicrobial susceptibility data in centers prescribing meropenem. The activity of meropenem and 7 broad-spectrum antimicrobials have been examined against 5208 bacterial isolates from 9 Turkish centers between 2000 and 2003. Cumulative susceptibility rates against all species of Enterobacteriaceae combined were ranked as follows: meropenem (99.3%), imipenem (97.6%), cefepime (80.0%), piperacillin-tazobactam (73.6%), ceftazidime (70.3%), ciprofloxacin (70.1%), cefotaxime (66.9%), and tobramycin (67.2%). The production of extended-spectrum beta-lactamases (ESBLs) was detected in 48.7% of Klebsiella pneumoniae and in 19.5% of Escherichia coli isolates. Of ESBL producing K. pneumoniae isolates, 75.7% were resistant to tobramycin, 40.3% to ciprofloxacin, and 48.3% to piperacillin-tazobactam. Only piperacillin/tazobactam and carbapenems were active against more than 50% of Pseudomonas aeruginosa at the National Committee for Clinical Laboratory Standards-susceptible breakpoint, and the carbapenems were the most active compounds against Acinetobacter spp. These data confirm the continued potency of meropenem against Enterobacteriaceae in units where it is actively being prescribed.

Empiric therapy for febrile neutropenia: what are the choices?

The management of febrile neutropenia has evolved gradually over the years toward a risk-adapted strategy based on validated prediction rules by risk of complications. The drug choice for empiric therapy is influenced by several factors, either related to the patient or to the institution. Microbiological distribution of offending pathogens and their pattern of susceptibility to antibiotics are continuously changing. New mechanisms of resistance in both Gram-negative and -positive bacteria have emerged. Guidelines and general statements should always be considered with the local epidemiology.

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.

Antibacterial dosage in intensive-care-unit patients based on pharmacokinetic/pharmacodynamic principles

PURPOSE OF REVIEW

Selection of the best antibiotic dosage regimen in intensive-care-unit patients is a critical factor for decreasing morbidity and mortality rates. The integration of pharmacokinetics and pharmacodynamics is essential to establishing an adequate therapy. Many studies on this issue have been published in recent years due to its relevance, some of which are commented upon in this review.

RECENT FINDINGS

Several studies have shown that it is feasible to theoretically forecast pharmacodynamic outcomes and select the most adequate antibiotic therapy with Monte Carlo simulations. Moreover, new strategies such as the use of continuous or extended intravenous beta-lactam infusions may considerably improve therapeutic efficacy.

SUMMARY

Future studies are needed in patients to assess the influence of selecting antibiotic therapy based on the impact of pharmacokinetic/pharmacodynamic on mortality, morbidity, cost, etc. It would be of special interest to evaluate this impact on patients with infections caused by multiresistant pathogens, whose mortality rates are even higher. Moreover, although studies such as this would not be easy, mainly due to the large number of patients required to obtain statistically significant results, they should be strongly encouraged because of the possible clinical and economic benefits.

Pharmacodynamic evaluation of meropenem and cefotaxime for pediatric meningitis: a report from the OPTAMA program

OBJECTIVE

To determine the probability of meropenem (Merrem, AstraZeneca Pharmaceuticals L.P., Wilmington, DE, USA) and cefotaxime (Claforan, Aventis Pharmaceuticals Inc., Bridgewater, NJ, USA) achieving bactericidal exposures in the cerebrospinal fluid against Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae.

METHODS

A 5,000-patient Monte Carlo simulation in a population of 10-year-old children with meningitis was conducted. Pediatric pharmacokinetic data were derived from the literature. Pathogen minimum inhibitory concentrations (MICs) were obtained from common bacteria that had caused meningitis collected during pediatric clinical trials. Time above the MIC exposures in the cerebrospinal fluid was calculated. Bactericidal exposure or probability of target attainment was defined as 40% and 50% time above the MIC for meropenem and cefotaxime, respectively. High cumulative fractions of responses were defined as >90% probability of target attainment against the populations of bacteria.

RESULTS

Meropenem was calculated to achieve 94.7%, 94.3%, and 96.1% cumulative fractions of response against S. pneumoniae, H. influenzae, and N. meningitidis, respectively. Cefotaxime only achieved a high likelihood of bactericidal attainment against N. meningitidis (91.6%). Against S. pneumoniae and H. influenzae, cefotaxime was only calculated to achieve 84.3% and 84.8% cumulative fractions of response, respectively.

CONCLUSION

In a simulated population of 10-year-old children, meropenem had a high likelihood of attaining bactericidal exposures in the cerebrospinal fluid. Cefotaxime had a >90% cumulative fraction of response against only N. meningitidis. Therefore, at the doses simulated, meropenem may be a more appropriate empiric choice for the treatment of bacterial meningitis in pediatric patients presumed to be caused by these pathogens until culture and susceptibility data are available.

Activity of meropenem and comparators against Pseudomonas aeruginosa and Acinetobacter spp. isolated in the MYSTIC Program, 2002-2004

This study examines the susceptibilities of meropenem and other broad-spectrum antimicrobials tested against bacterial isolates collected from hospitalized patients during 2002-2004 from worldwide medical centers participating in the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program. The in vitro activity of meropenem and 5 comparator antimicrobial agents was assessed against Pseudomonas aeruginosa and Acinetobacter spp. Generally, the susceptibility of Australasian and North American isolates was higher than that of the European and South American isolates. The rank order of activity of the antimicrobial agents tested against a worldwide collection of P. aeruginosa was piperacillin/tazobactam (77.7% susceptible) > meropenem (75.4%) > ceftazidime (70.0%) > imipenem (69.7%) > gentamicin (66.1%) > ciprofloxacin (62.0%). Against a worldwide collection of Acinetobacter spp. meropenem (76.1% susceptible) was the most active compound followed by imipenem (74.7%) > gentamicin (51.9%) > ciprofloxacin (40.5%) > piperacillin/tazobactam (39.8%) > ceftazidime (38.1%). The carbapenems appear to be a valuable option for the treatment of serious nosocomial infections caused by P. aeruginosa or Acinetobacter spp. over a broad geographical region.

An overview of the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program: 1997-2004

This overview provides a summary of the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program over an 8-year period from 1997 to 2004. The evolution of the MYSTIC Program is described, as well as its design compared with other surveillance programs. In addition, the global MYSTIC Program data, published to date, are summarized, and the empiric use of carbapenems, their current indications, and meropenem usage versus resistance was discussed. From 1997 to 2004, 120 medical centers that were actively prescribing meropenem in 32 countries worldwide participated in the program. The MYSTIC Program results demonstrate the sustained potency and continued effectiveness of meropenem globally against clinically relevant Gram-negative and Gram-positive pathogens including extended spectrum beta-lactamase- and AmpC beta-lactamase-producing organisms, which may also display resistance to the fluoroquinolones and/or aminoglycosides. Furthermore, in centers actively prescribing meropenem, resistance to meropenem is not increasing despite greater resistance among the comparator antimicrobial agents. Thus, antipseudomonal carbapenems such as meropenem and imipenem remain an effective treatment option.

Making the most of surveillance studies: summary of the OPTAMA Program

Antibiotic surveillance studies lack consideration of pharmacodynamics and provide little information about optimal dosing. By using minimum inhibitory concentration (MIC) data derived from a global surveillance study and Monte Carlo simulation, the Optimizing Pharmacodynamic Target Attainment using the MYSTIC Antibiogram (OPTAMA) Program was established to impart greater understanding of the ability to attain pharmacodynamic exposure for specific dosing regimens and their relationship with percent susceptibility. Early OPTAMA studies focused on determining the cumulative fraction of response (CFR) for various antibiotics against Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa regionally in Europe and the Americas. Later reports considered the prevalence of specific bacteria causing infections to estimate the CFR for empiric therapy of pneumonia, bloodstream, complicated skin/skin structure, and intra-abdominal infections. Collectively, the approach of the OPTAMA Program provides a novel tool that complements susceptibility data to help in the selection of appropriate empirical antibiotic therapy at the national, regional, and institutional level.

Prevalence and antimicrobial susceptibility data for extended-spectrum β-lactamase– and AmpC-producing Enterobacteriaceae from the MYSTIC Program in Europe and the United States (1997–2004)

This article presents prevalence and susceptibility data from the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program in Europe (1997-2004) and the United States (1999-2004) for Enterobacteriaceae producing extended-spectrum beta-lactamase (ESBL) and/or AmpC beta-lactamases. For ESBL-producing isolates, the prevalence of Escherichia coli and Klebsiella spp. in Europe and Enterobacter spp. in the United States increased over time. For AmpC-producing isolates, the prevalence of Enterobacter spp. and Citrobacter spp. decreased over time in Europe and the United States, respectively. Compared with other antimicrobial agents, meropenem and imipenem had greatest activity against ESBL-producing E. coli and Klebsiella spp. in both Europe (96.9-100.0%) and the United States (100.0%). Such activity was also found for AmpC-producing Enterobacteriaceae in Europe (50.0-100.0%), and Enterobacter spp. and Citrobacter spp. from the United States (100.0% for both). The continued efficacy of carbapenems such as meropenem confirms that these remain first-line agents for treatment of nosocomial infections caused by Enterobacteriaceae-producing ESBL or AmpC beta-lactamases.