Pharmacokinetic and pharmacodynamic evaluation of two dosing regimens for piperacillin-tazobactam

Breaking Down the Breakpoints: Rationale for the 2022 Clinical and Laboratory Standards Institute Revised Piperacillin-Tazobactam Breakpoints Against Enterobacterales

Piperacillin-tazobactam (PTZ) is one of the most common antibiotics administered to hospitalized patients. Its broad activity against gram-negative, gram-positive, and anaerobic pathogens; efficacy in clinical trials across diverse infection types and patient populations; and generally favorable toxicity profile make it a particularly appealing antibiotic agent. PTZ susceptibility interpretive criteria (ie, breakpoints) for the Enterobacterales were initially established in 1992, as the drug was undergoing approval by the US Food and Drug Administration. In the ensuing 30 years, changes in the molecular epidemiology of the Enterobacterales and its impact on PTZ susceptibility testing, mounting pharmacokinetic/pharmacodynamic data generated from sophisticated techniques such as population pharmacokinetic modeling and Monte Carlo simulation, and disturbing safety signals in a large clinical trial prompted the Clinical Laboratory and Standards Institute (CLSI) to review available evidence to determine the need for revision of the PTZ breakpoints for Enterobacterales. After an extensive literature review and formal voting process, the susceptibility criteria were revised in the 2022 CLSI M100 document to the following: ≤8/4 µg/mL (susceptible), 16/4 µg/mL (susceptible dose-dependent), and ≥32/4 µg/mL (resistant). Herein, we provide a brief overview of the CLSI process of antibiotic breakpoint revisions and elaborate on the available data that ultimately led to the decision to revise the PTZ breakpoints.

Simple HPLC-UV Method for Piperacillin/Tazobactam Assay in Human Plasma

BACKGROUND

Piperacillin (Pip)/tazobactam (Taz) is a broad-spectrum antimicrobial agent that has been commonly used in the intensive care unit for severe and life-threatening infections. Recent evidence suggests that therapeutic drug monitoring (TDM) for Pip could be beneficial in clinical practice to facilitate dose optimization and increase the odds of treatment success. The aim was to develop and validate a sensitive and simple high-performance liquid chromatography (HPLC) method for the simultaneous quantification of Pip and Taz in human plasma.

METHODS

Samples (0.3 mL) were deproteinized with acetonitrile. The supernatant was evaporated and then reconstituted and injected into the HPLC. The chromatographic analysis was carried out by using the C18 column and gradient elution with the acetonitrile:water mobile phase mixture with 0.1% trifluoracetic acid at a flow rate of 0.8 mL/min using a UV detector at 218 nm.

RESULTS

The method had acceptable linearity (r² > 0.99) over the concentration ranges of 0.5-400 μg/mL and 1-100 μg/mL for Pip and Taz, respectively. The method demonstrated acceptable inter- and intra-day precision and accuracy within ±20% with adequate stability results.

CONCLUSION

The developed method is sensitive and simple and utilizes simple sample preparation and elution steps, making it suitable and practical for Pip/Taz TDM.

The primary pharmacology of ceftazidime/avibactam: in vivo translational biology and pharmacokinetics/pharmacodynamics (PK/PD)

This review describes the translational in vivo and non-clinical pharmacokinetics/pharmacodynamics (PK/PD) research that supported clinical trialling and subsequently licensing approval of ceftazidime/avibactam, a new β-lactam/β-lactamase inhibitor combination aimed at the treatment of infections by Enterobacterales and Pseudomonas aeruginosa. The review thematically follows on from the co-published article, Nichols et al. (J Antimicrob Chemother 2022; dkac171). Avibactam protected ceftazidime in animal models of infection with ceftazidime-resistant, β-lactamase-producing bacteria. For example, a single subcutaneous dose of ceftazidime at 1024 mg/kg yielded little effect on the growth of ceftazidime-resistant, blaKPC-2-carrying Klebsiella pneumoniae in the thighs of neutropenic mice (final counts of 4 × 108 to 8 × 108 cfu/thigh). In contrast, co-administration of avibactam in a 4:1 ratio (ceftazidime:avibactam) was bactericidal in the same model (final counts of 2 × 104 to 3 × 104 cfu/thigh). In a rat abdominal abscess model, therapy with ceftazidime or ceftazidime/avibactam (4:1 w/w) against blaKPC-2-positive K. pneumoniae resulted in 9.3 versus 3.3 log cfu/abscess, respectively, after 52 h. With respect to PK/PD, in Monte Carlo simulations, attainment of unbound drug exposure targets (ceftazidime fT>8 mg/L and avibactam fT>1 mg/L, each for 50% of the dosing interval) for the labelled dose of ceftazidime/avibactam (2 and 0.5 g, respectively, q8h by 2 h IV infusion), including dose adjustments for patients with impaired renal function, ranged between 94.8% and 99.6% of patients, depending on the infection modelled.

Murine Model for Measuring Effects of Humanized-Dosing of Antibiotics on the Gut Microbiome

There is a current need for enhancing our insight in the effects of antimicrobial treatment on the composition of human microbiota. Also, the spontaneous restoration of the microbiota after antimicrobial treatment requires better understanding. This is best addressed in well-defined animal models. We here present a model in which immune-competent or neutropenic mice were administered piperacillin-tazobactam (TZP) according to human treatment schedules. Before, during and after the TZP treatment, fecal specimens were longitudinally collected at established intervals over several weeks. Gut microbial taxonomic distribution and abundance were assessed through culture and molecular means during all periods. Non-targeted metabolomics analyses of stool samples using Quadrupole Time of Flight mass spectrometry (QTOF MS) were also applied to determine if a metabolic fingerprint correlated with antibiotic use, immune status, and microbial abundance. TZP treatment led to a 5–10-fold decrease in bacterial fecal viability counts which were not fully restored during post-antibiotic follow up. Two distinct, relatively uniform and reproducible restoration scenarios of microbiota changes were seen in post TZP-treatment mice. Post-antibiotic flora could consist of predominantly Firmicutes or, alternatively, a more diverse mix of taxa. In general, the pre-treatment microbial communities were not fully restored within the screening periods applied. A new species, closely related to Eubacterium siraeum, Mageeibacillus indolicus, and Saccharofermentans acetigenes, became predominant post-treatment in a significant proportion of mice, identified by 16S rRNA gene sequencing. Principal component analysis of QTOF MS of mouse feces successfully distinguished treated from non-treated mice as well as immunocompetent from neutropenic mice. We observe dynamic but distinct and reproducible responses in the mouse gut microbiota during and after TZP treatment and propose the current murine model as a useful tool for defining the more general post-antibiotic effects in the gastro-intestinal ecosystem where humanized antibiotic dosing may ultimately facilitate extrapolation to humans.

Pharmacokinetics, Tissue Distribution, and Efficacy of VIO-001 (Meropenem/Piperacillin/Tazobactam) for Treatment of Methicillin-Resistant Staphylococcus aureus Bacteremia in Immunocompetent Rabbits with Chronic Indwelling Vascular Catheters

Methicillin-resistant Staphylococcus aureus (MRSA) infections of surgically implanted subcutaneous vascular catheters (SISVCs) cause serious morbidity in patients with chronic illnesses. Previous in vitro and murine models demonstrated the synergistic interaction of equimolar concentrations of meropenem/piperacillin/tazobactam (MPT) (VIO-001) against MRSA infection. We investigated the pharmacokinetics (PK) and efficacy of VIO-001 for the treatment of MRSA bacteremia in immunocompetent rabbits with SISVCs. In PK studies, we determined that optimal dosing to achieve a time above 4× MIC (T_>4×MIC) of a duration of 3 to 3.30 h required a 1-h infusion with every-4-h (Q4h) dosing. Study groups in efficacy experiments consisted of MPT combinations of 100/150/100 mg/kg of body weight (MPT100), 200/300/200 mg/kg (MPT200), and 400/600/400 mg/kg (MPT400); vancomycin (VAN) at 15 mg/kg; and untreated controls (UC). The inoculum of MRSA isolate USA300-TCH1516 (1 × 10³ organisms) was administered via the SISCV on day 1 and locked for 24 h. The 8-day therapy started at 24 h postinoculation. There was a significant reduction of MRSA in blood cultures from the SISVCs in all treatment groups, with full clearance on day 4, versus UCs (P < 0.05). Consistent with the clearance of SISVC-related infection, full eradication of MRSA was achieved in lungs, heart, liver, spleen, and kidneys at the end of the study versus UC (P < 0.01). These results strongly correlated with time-kill data, where MPT in the range of 4/6/4 μg/ml to 32/48/32 μg/ml demonstrated a significant 6-log decrease in the bacterial burden versus UC (P < 0.01). In summary, VIO-001 demonstrated a favorable PK/pharmacodynamic (PD) profile and activity against SISCV MRSA infection, bacteremia, and disseminated infection. This rabbit model provides a new system for understanding new antimicrobial agents against MRSA SISVC-related infection, and these data provide a basis for future clinical investigation.

Impact of Intraoperative Cell Salvage on Concentrations of Antibiotics Used for Surgical Prophylaxis

Intraoperative cell salvage (IOCS) is used to administer autologous blood lost during surgery. We studied antibiotic disposition through an ex vivo IOCS system for vancomycin, piperacillin, ampicillin, and cefazolin. Only 2% ± 1% of antibiotic inoculated in whole blood was recovered in the IOCS reinfusion bag, whereas 97% ± 17% was found in the waste. These observations were confirmed for ampicillin in two patients undergoing liver transplantation. Studies measuring the impact of IOCS on perioperative antibiotic concentrations are warranted.

Role of transporters in the disposition of a novel β-lactamase inhibitor: relebactam (MK-7655)

OBJECTIVES

To identify the transporters involved in renal elimination of relebactam, and to assess the potential of relebactam as a perpetrator or victim of drug-drug interactions (DDIs) for major drug transporters.

METHODS

A series of bidirectional transport, uptake and inhibition studies were conducted in vitro using transfected cell lines and membrane vesicles. The inhibitory effects of relebactam on major drug transporters, as well as the inhibitory effects of commonly used antibiotics/antifungals on organic anion transporter (OAT) 3-mediated uptake of relebactam, were assessed.

RESULTS

Relebactam was shown to be a substrate of OAT3, OAT4, and multidrug and toxin extrusion (MATE) proteins MATE1 and MATE2K. Relebactam did not show profound inhibition across a panel of transporters, including organic anion-transporting polypeptides 1B1 and 1B3, OAT1, OAT3, organic cation transporter 2, MATE1, MATE2K, breast cancer resistance protein, multidrug resistance protein 1 and the bile salt export pump. Among the antibiotics/antifungals assessed for potential DDIs, probenecid demonstrated the most potent in vitro inhibition of relebactam uptake; however, such in vitro data did not translate into clinically relevant DDIs, suggesting that relebactam can be co-administered with OAT inhibitors, such as probenecid.

CONCLUSIONS

Overall, relebactam has low potential to be a victim or perpetrator of DDIs with major drug transporters.

Piperacillin-Tazobactam-Resistant/Third-Generation Cephalosporin-Susceptible Escherichia coli and Klebsiella pneumoniae Isolates: Resistance Mechanisms and In vitro-In vivo Discordance

We previously reported the detection of Escherichia coli and Klebsiella pneumoniae that displayed in vitro piperacillin-tazobactam (TZP) resistance but were susceptible to third-generation cephalosporins (TZP-R/Ceph3-S). In this study, we assessed the phenotypic and genotypic profiles of 12 clinical non-clonal TZP-R/Ceph3-S E. coli and K. pneumoniae isolates derived from bloodstream infections. Whole-genome sequencing revealed that most of the TZP-R/Ceph3-S E. coli and K. pneumoniae isolates examined harbored bla_TEM-1 and bla_SHV-1 genes, respectively, but none harbored extended-spectrum β-lactamase, AmpC β-lactamase or carbapenemase genes. Increasing the tazobactam concentration from 4 mg/L to 16 mg/L restored TZP in vitro susceptibility among E. coli isolates expressing TEM-1, but had minimal impact on the susceptibility of K. pneumoniae to TZP. Real-time qPCR analysis showed that bla_TEM-1 expression was amplified in TZP-R E. coli upon incubation with sub-inhibitory TZP concentrations. Using an immunocompetent murine septicemia model, the efficacy of TZP against TZP-R/Ceph3-S isolates was assessed using TZP doses that mimicked human plasma exposures following intravenous (IV) administration of TZP 4.5 g q6h over 0.5 h for 24 h. Efficacy was assessed by survival through 96 h. There was high mortality in untreated control mice for all tested isolates. Compared with controls, TZP human-simulated exposure significantly improved survival for all TZP-R/Ceph3-S E. coli and K. pneumoniae isolates examined (P < 0.05). Thus, TZP was associated with remarkable in vivo activity against TZP-R/Ceph3-S E. coli and K. pneumoniae despite the observed resistance in vitro.

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.

Is One Sample Enough? β-Lactam Target Attainment and Penetration into Epithelial Lining Fluid Based on Multiple Bronchoalveolar Lavage Sampling Time Points in a Swine Pneumonia Model

Describing the disposition of antimicrobial agents at the site of infection is crucial to guide optimal dosing for investigational agents. For antibiotics in development for the treatment of nosocomial pneumonia, concentrations in the epithelial lining fluid (ELF) of the lung are frequently determined from a bronchoscopy at a single time point. The influence of profiles constructed from a single ELF concentration point for each subject has never been reported. This study compares the pharmacokinetics of two β-lactams, ceftolozane and piperacillin, among different ELF sampling approaches using simulated human regimens in a swine pneumonia model. Plasma and ELF concentration-time profiles were characterized in two-compartment models by the use of robustly sampled ELF concentrations and by the random selection of one or two ELF concentrations from each swine. A 5,000-subject Monte Carlo simulation was performed for each model to define the ELF penetration, as described by the ratio of the area under the concentration curve (AUC) for ELF to the AUC for free drug in plasma (AUC_ELF/fAUC_plasma) and the probability of target attainment (PTA). Given the intersubject variability of the ELF penetrations observed, differences between the models developed using robust numbers of ELF samples versus one or two ELF samples per swine were minimal for both drugs (maximum dispersion < 20%). Using a threshold exposure target of 60% of the time that the free drug concentration remains above the MIC target, the ceftolozane and piperacillin regimens achieved PTAs of ≥90% at MICs of up to 4 and 1 μg/ml, respectively, among the different ELF sampling strategies. These models suggest that the ELF models constructed with concentrations from sparse ELF sampling time points result in exposure estimates similar to those constructed from robustly sampled ELF profiles.

Scaling beta-lactam antimicrobial pharmacokinetics from early life to old age

AIMS

Beta-lactam dose optimization in critical care is a current priority. We aimed to review the pharmacokinetics (PK) of three commonly used beta-lactams (amoxicillin ± clavulanate, piperacillin-tazobactam and meropenem) to compare PK parameters reported in critically and noncritically ill neonates, children and adults, and to investigate whether allometric and maturation scaling principles could be applied to describe changes in PK parameters through life.

METHODS

A systematic review of PK studies of the three drugs was undertaken using MEDLINE and EMBASE. PK parameters and summary statistics were extracted and scaled using allometric principles to 70 kg individual for comparison. Pooled data were used to model clearance maturation and decline using a sigmoidal (Hill) function.

RESULTS

A total of 130 papers were identified. Age ranged from 29 weeks to 82 years and weight from 0.9-200 kg. PK parameters from critically ill populations were reported with wider confidence intervals than those in healthy volunteers, indicating greater PK variability in critical illness. The standard allometric size and sigmoidal maturation model adequately described increasing clearance in neonates, and a sigmoidal model was also used to describe decline in older age. Adult weight-adjusted clearance was achieved at approximately 2 years postmenstrual age. Changes in volume of distribution were well described by the standard allometric model, although amoxicillin data suggested a relatively higher volume of distribution in neonates.

CONCLUSIONS

Critical illness is associated with greater PK variability than in healthy volunteers. The maturation models presented will be useful for optimizing beta-lactam dosing, although a prospective, age-inclusive study is warranted for external validation.

Safety, Tolerability, and Pharmacokinetics of 3 g of Ceftolozane/Tazobactam in Healthy Adults: A Randomized, Placebo-Controlled, Multiple-Dose Study

Ceftolozane/tazobactam is an antibacterial approved at 1.5 g (1g/0.5 g) every 8 hours (q8h); higher doses may provide additional benefits in difficult-to-treat infections. We conducted a phase I trial in healthy adults evaluating safety, tolerability, and pharmacokinetics of 3 g (2 g/1 g) ceftolozane/tazobactam administered q8h for 10 days. Sixteen participants were randomized (2:1:1) to 3 g ceftolozane/tazobactam, 1.5 g ceftolozane/tazobactam, or placebo. Participants underwent regular safety and plasma drug level assessments, with a follow-up safety visit 7 days after completion. No adverse events (AEs) were reported with placebo; 75% of participants in the 1.5-g and 50% in the 3-g arm experienced AEs. AE types were similar between the ceftolozane/tazobactam groups; all AEs were mild. No participants experienced clinically meaningful laboratory assessment or electrocardiogram abnormalities. Both ceftolozane and tazobactam exhibited dose-proportional pharmacokinetics without accumulation and without substantial differences in clearance and volume of distribution between groups. In the 3-g group, mean ceftolozane parameters were: peak concentration 104 μg/mL (day 1), 112 μg/mL (day 10); half-life 3 hours (day 10); area under the concentration-time curve (AUC_(0-t) ) 272 μg·h/mL (day 1), 300μg·h/mL (day 10). Mean tazobactam parameters were: peak concentration 28 μg/mL (day 1), 26 μg/mL (day 10); half-life 1 hour (day 10); AUC_(0-t) 47μg·h/mL (day 1), 41μg·h/mL (day 10). Administration of 3 g ceftolozane/tazobactam q8h for 10 days was safe and well tolerated in healthy volunteers.

Management of KPC-producing Klebsiella pneumoniae infections

BACKGROUND

Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae (KPC-KP) has become one of the most important contemporary pathogens, especially in endemic areas.

AIMS

To provide practical suggestion for physicians dealing with the management of KPC-KP infections in critically ill patients, based on expert opinions.

SOURCES

PubMed search for relevant publications related to the management of KPC-KP infections.

CONTENTS

A panel of experts developed a list of 12 questions to be addressed. In view of the current lack of high-level evidence, they were asked to provide answers on the bases of their knowledge and experience in the field. The panel identified several key aspects to be addressed when dealing with KPC-KP in critically ill patients (preventing colonization in the patient, preventing infection in the colonized patient and colonization of his or her contacts, reducing mortality in the infected patient by rapidly diagnosing the causative agent and promptly adopting the best therapeutic strategy) and provided related suggestions that were based on the available observational literature and the experience of panel members.

IMPLICATIONS

Diagnostic technologies could speed up the diagnosis of KPC-KP infections. Combination treatment should be preferred to monotherapy in cases of severe infections. For non-critically ill patients without severe infections, results from randomized clinical trials are needed for ultimately weighing benefits and costs of using combinations rather than monotherapy. Multifaceted infection control interventions are needed to decrease the rates of colonization and cross-transmission of KPC-KP.

Prolonged versus Intermittent Infusion of β-Lactams for the Treatment of Nosocomial Pneumonia: A Meta-Analysis

BACKGROUND

The primary objective of this meta-analysis is aimed at determining whether β-lactams prolonged infusion in patients with nosocomial pneumonia (NP) results in higher cure rate and improved mortality compared to intermittent infusion.

MATERIALS AND METHODS

Relevant studies were identified from searches of MEDLINE, EMBASE, and CENTRAL from inception to September 1st, 2015. All published articles which evaluated the outcome of extended/continuous infusion of antimicrobial therapy versus intermittent infusion therapy in the treatment of NP were reviewed.

RESULTS

A total of ten studies were included in the analysis involving 1,051 cases of NP. Prolonged infusion of β-lactams was associated with higher clinical cure rate (OR 2.45, 95% CI, 1.12, 5.37) compared to intermittent infusion. However, there was no significant difference in mortality (OR 0.85, 95% CI 0.63-1.15) between the two groups. Subgroup analysis for β-lactam subclasses and for severity of illness showed comparable outcomes.

CONCLUSION

The limited data available suggest that reduced clinical failure rates when using prolonged infusions of β-lactam antibiotics in critically ill patients with NP. More detailed studies are needed to determine the impact of such strategy on mortality in this patient population.

Development of an HPLC Method for the Determination of Ceftolozane/Tazobactam in Biological and Aqueous Matrixes

Herein, we report the development and validation of an HPLC method to analyze ceftolozane and tazobactam simultaneously in human plasma, human serum, swine serum and saline matrixes. A reversed-phase column was used with a UV detector set at 260 nm and switched to 218 nm. The mobile phase consisted of methanol and sodium phosphate buffer at a flow rate of 1.1 mL/min. Cefepime was used as the internal standard. The standard curves were linear over a range of 0.4-50 μg/mL. This methodology represents a simple, reproducible approach to the determination of drug concentrations with sufficient accuracy and precision for pharmacokinetic studies undertaken with this recently FDA-approved antimicrobial therapy.

Utilizing Monte Carlo Simulations to Optimize Institutional Empiric Antipseudomonal Therapy

Pseudomonas aeruginosa is a common pathogen implicated in nosocomial infections with increasing resistance to a limited arsenal of antibiotics. Monte Carlo simulation provides antimicrobial stewardship teams with an additional tool to guide empiric therapy. We modeled empiric therapies with antipseudomonal β-lactam antibiotic regimens to determine which were most likely to achieve probability of target attainment (PTA) of ≥90%. Microbiological data for P. aeruginosa was reviewed for 2012. Antibiotics modeled for intermittent and prolonged infusion were aztreonam, cefepime, meropenem, and piperacillin/tazobactam. Using minimum inhibitory concentrations (MICs) from institution-specific isolates, and pharmacokinetic and pharmacodynamic parameters from previously published studies, a 10,000-subject Monte Carlo simulation was performed for each regimen to determine PTA. MICs from 272 isolates were included in this analysis. No intermittent infusion regimens achieved PTA ≥90%. Prolonged infusions of cefepime 2000 mg Q8 h, meropenem 1000 mg Q8 h, and meropenem 2000 mg Q8 h demonstrated PTA of 93%, 92%, and 100%, respectively. Prolonged infusions of piperacillin/tazobactam 4.5 g Q6 h and aztreonam 2 g Q8 h failed to achieved PTA ≥90% but demonstrated PTA of 81% and 73%, respectively. Standard doses of β-lactam antibiotics as intermittent infusion did not achieve 90% PTA against P. aeruginosa isolated at our institution; however, some prolonged infusions were able to achieve these targets.

Pharmacokinetics and pharmacodynamics of extended-infusion piperacillin/tazobactam in adult patients with cystic fibrosis-related acute pulmonary exacerbations

OBJECTIVES

Given the high frequency of acute pulmonary exacerbations due to Pseudomonas aeruginosa in patients with cystic fibrosis (CF), piperacillin/tazobactam is commonly used in empirical regimens. While extended-infusion piperacillin/tazobactam has been employed as one strategy to optimize this agent's pharmacodynamics, this approach has not been well characterized in patients with CF. The objectives of this study were to characterize the pharmacokinetics and pharmacodynamics of extended-infusion piperacillin/tazobactam in adult patients with CF and derive optimized piperacillin/tazobactam dosing recommendations.

METHODS

Six serum samples were collected from nine adult patients with CF hospitalized for acute pulmonary exacerbations who received 3/0.375 g of piperacillin/tazobactam intravenously for 4 h every 8 h. Population pharmacokinetic models were fitted to the data utilizing first-order, Michaelis-Menten (MM) and parallel first-order/MM clearance. Monte Carlo simulations were performed to determine the probability of target attainment (PTA) for regimens where free piperacillin concentrations were above the MIC for at least 50% of the dosing interval.

RESULTS

The model incorporating MM clearance best described the data. Results of our simulation revealed that piperacillin/tazobactam dosed at 3-4 g for 30 min every 6-8 h led to <90% PTA against MIC values >4 mg/L. More intensive prolonged infusion regimens than are commonly used in practice, such as continuous infusions or 3 h infusions every 6 h, were needed to maximize the PTA for MICs ≥ 8 mg/L.

CONCLUSIONS

Intensive prolonged infusion regimens are the best option to ensure optimal exposures against most susceptible isolates in adult patients with CF.

Comparison of 2 blood culture media shows significant differences in bacterial recovery for patients on antimicrobial therapy

BACKGROUND

Antimicrobial removal devices in blood culture media are designed to remove antibiotics from the blood culture solution, thereby facilitating bacterial growth. How well these devices function clinically has not been established.

METHODS

All blood drawn for culture from adult inpatients and emergency department visitors in a level I trauma center was placed in paired BACTEC Plus and BacT/Alert FAN culture media and studied simultaneously, consecutively, and prospectively between 1 February and 30 September 2011. All cultures were processed per standard laboratory protocols.

RESULTS

Of 9395 total cultures collected, 1219 (13%) were positive, 831 were included, and 524 (33%) contained pathogens. BACTEC had a 4.5-hour faster detection time (P < .0001), and isolated exclusively 182 of 524 (35%; P < .001) pathogens, 136 of 345 (39%) of the gram-positive cocci (P < .001), 48 of 175 (27%; P = .02) of the gram-negative rods, 101 of 195 (52%) of Staphylococcus aureus (P < .001), and 59 of 120 (49%; P = .004) septic events. If active antibiotics had been dosed 0-4 or 4-48 hours prior to culture collection, the odds of that culture growing in BACTEC were 4.8- and 5.2-fold greater, respectively, than of growing in BacT/Alert (P < .0001). Both were equivalent in the recovery of yeast and when no antimicrobials were dosed.

CONCLUSIONS

BACTEC media has faster time to detection and increased bacterial recovery over the BacT/Alert media in the following categories: overall growth, pathogens, septic events, gram-positive cocci, gram-negative rods, Staphylococcus aureus, and cultures where antimicrobials were dosed up to 48 hours before culture collection.

Comparison of antimicrobial pharmacokinetic/pharmacodynamic breakpoints with EUCAST and CLSI clinical breakpoints for Gram-positive bacteria

This study compared the susceptibility breakpoints based on pharmacokinetic/pharmacodynamic (PK/PD) models and Monte Carlo simulation with those defined by the Clinical and Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) for antibiotics used for the treatment of infections caused by Gram-positive bacteria. A secondary objective was to evaluate the probability of achieving the PK/PD target associated with the success of antimicrobial therapy. A 10,000-subject Monte Carlo simulation was executed to evaluate 13 antimicrobials (47 intravenous dosing regimens). Susceptibility data were extracted from the British Society for Antimicrobial Chemotherapy database for bacteraemia isolates. The probability of target attainment and the cumulative fraction of response (CFR) were calculated. No antibiotic was predicted to be effective (CFR≥90%) against all microorganisms. The PK/PD susceptibility breakpoints were also estimated and were compared with CLSI and EUCAST breakpoints. The percentages of strains affected by breakpoint discrepancies were calculated. In the case of β-lactams, breakpoint discrepancies affected <15% of strains. However, higher differences were detected for low doses of vancomycin, daptomycin and linezolid, with PK/PD breakpoints being lower than those defined by the CLSI and EUCAST. If this occurs, an isolate will be considered susceptible based on CLSI and EUCAST breakpoints although the PK/PD analysis predicts failure, which may explain treatment failures reported in the literature. This study reinforces the idea of considering not only the antimicrobial activity but also the dosing regimen to increase the probability of clinical success of an antimicrobial treatment.

Population pharmacokinetics of extended-infusion piperacillin-tazobactam in hospitalized patients with nosocomial infections

While extended infusions of piperacillin-tazobactam (TZP) are increasingly used in practice, the effect of infusion on the pharmacokinetic (PK) profile of TZP has not been widely assessed. To assess its effect on the pharmacokinetic profile of TZP, seven serum samples were collected from 11 hospitalized patients who received 3.375 g TZP intravenously for 4 h every 8 h. Population pharmacokinetic models were fit to the PK data utilizing first-order, Michaelis-Menten (MM), and parallel first-order/MM clearance. A population PK model with first-order clearance was fit to the tazobactam PK data. Monte Carlo simulations (MCSs) were used to determine the most effective administration schedule to ensure that free piperacillin concentrations were above the MIC for at least 50% of the dosing interval (50% fT>MIC) and to quantify the extent of the nonlinear clearance. The model incorporating parallel linear/MM clearance best fit the piperacillin PK data. The MCSs demonstrated that approximately 50% of the administered piperacillin is cleared by the nonlinear clearance mechanism. The results of the MCSs also revealed that more intensive TZP extended infusion dosing schemes (3.375 to 4.5 g intravenously [3-h infusion] every 6 h) than those commonly used in clinical practice were needed to maximize the 50% fT>MIC for MICs of ≥8 mg/liter. This study suggests that extended infusion of TZP is the most effective method of administration for patients with nosocomial infections. Due to the hyperclearance nature of the hospitalized patient populations studied, more intensive TZP dosing regimens may be needed to maximize fT>MIC in certain hospitalized populations.

Pharmacokinetics and pharmacodynamics of piperacillin-tazobactam in 42 patients treated with concomitant CRRT

BACKGROUND AND OBJECTIVES

Current recommendations for piperacillin-tazobactam dosing in patients receiving continuous renal replacement therapy originate from studies with relatively few patients and lower continuous renal replacement therapy doses than commonly used today. This study measured the pharmacokinetic and pharmacodynamic characteristics of piperacillin-tazobactam in patients treated with continuous renal replacement therapy using contemporary equipment and prescriptions.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A multicenter prospective observational study in the intensive care units of two academic medical centers was performed, enrolling patients with AKI or ESRD receiving piperacillin-tazobactam while being treated with continuous renal replacement therapy. Pregnant women, children, and patients with end stage liver disease were excluded from enrollment. Plasma and continuous renal replacement therapy effluent samples were analyzed for piperacillin and tazobactam levels using HPLC. Pharmacokinetic and pharmacodynamic parameters were calculated using standard equations. Multivariate analyses were used to examine the association of patient and continuous renal replacement therapy characteristics with piperacillin pharmacokinetic parameters.

RESULTS

Forty-two of fifty-five subjects enrolled had complete sampling. Volume of distribution (median=0.38 L/kg, intraquartile range=0.20 L/kg) and elimination rate constants (median=0.104 h(-1), intraquartile range=0.052 h(-1)) were highly variable, and clinical parameters could explain only a small fraction of the large variability in pharmacokinetic parameters. Probability of target attainment for piperacillin was 83% for total drug but only 77% when the unbound fraction was considered.

CONCLUSIONS

There is significant patient to patient variability in pharmacokinetic/pharmacodynamic parameters in patients receiving continuous renal replacement therapy. Many patients did not achieve pharmacodynamic targets, suggesting that therapeutic drug monitoring might optimize therapy.

In vivo comparison of CXA-101 (FR264205) with and without tazobactam versus piperacillin-tazobactam using human simulated exposures against phenotypically diverse gram-negative organisms

CXA-101 is a novel antipseudomonal cephalosporin with enhanced activity against Gram-negative organisms displaying various resistance mechanisms. This study evaluates the efficacy of exposures approximating human percent free time above the MIC (%fT > MIC) of CXA-101 with or without tazobactam and piperacillin-tazobactam (TZP) against target Gram-negative organisms, including those expressing extended-spectrum β-lactamases (ESBLs). Sixteen clinical Gram-negative isolates (6 Pseudomonas aeruginosa isolates [piperacillin-tazobactam MIC range, 8 to 64 μg/ml], 4 Escherichia coli isolates (2 ESBL and 2 non-ESBL expressing), and 4 Klebsiella pneumoniae isolates (3 ESBL and 1 non-ESBL expressing) were used in an immunocompetent murine thigh infection model. After infection, groups of mice were administered doses of CXA-101 with or without tazobactam (2:1) designed to approximate the %fT > MIC observed in humans given 1 g of CXA-101 with or without tazobactam every 8 h as a 1-h infusion. As a comparison, groups of mice were administered piperacillin-tazobactam doses designed to approximate the %fT > MIC observed in humans given 4.5 g piperacillin-tazobactam every 6 h as a 30-min infusion. Predicted piperacillin-tazobactam %fT > MIC exposures of greater than 40% resulted in static to >1 log decreases in CFU in non-ESBL-expressing organisms with MICs of ≤32 μg/ml after 24 h of therapy. Predicted CXA-101 with or without tazobactam %fT > MIC exposures of ≥37.5% resulted in 1- to 3-log-unit decreases in CFU in non-ESBL-expressing organisms, with MICs of ≤16 μg/ml after 24 h of therapy. With regard to the ESBL-expressing organisms, the inhibitor combinations showed enhanced CFU decreases versus CXA-101 alone. Due to enhanced in vitro potency and resultant increased in vivo exposure, CXA-101 produced statistically significant reductions in CFU in 9 isolates compared with piperacillin-tazobactam. The addition of tazobactam to CXA-101 produced significant reductions in CFU for 7 isolates compared with piperacillin-tazobactam. Overall, human simulated exposures of CXA-101 with or without tazobactam demonstrated improved efficacy versus piperacillin-tazobactam.

Use of empiric antimicrobial therapy in neutropenic fever. Australian Consensus Guidelines 2011 Steering Committee

Administration of empiric antimicrobial therapy is standard practice in the management of neutropenic fever, but there remains considerable debate about the selection of an optimal regimen. In view of emerging evidence regarding efficacy and toxicity differences between empiric treatment regimens, and strong evidence of heterogeneity in clinical practice, the current guidelines were developed to provide Australian clinicians with comprehensive guidance for selecting an appropriate empiric strategy in the setting of neutropenic fever. Beta-lactam monotherapy is presented as the treatment of choice for all clinically stable patients while early treatment with combination antibiotic therapy is considered for patients at higher risk. Due consideration is given to the appropriate use of glycopeptides in this setting. Several clinical caveats, accounting for institution- and patient-specific risk factors, are provided to help guide the judicious use of the agents described. Detailed recommendations are also provided regarding time to first dose, timing of blood cultures, selection of a first-line antibiotic regimen, subsequent modification of antibiotic choice and cessation of therapy.

Tazobactam/piperacillin for moderate-to-severe pneumonia in patients with risk for aspiration: comparison with imipenem/cilastatin

BACKGROUND

Treatment of aspiration pneumonia is becoming an important issue due to aging of populations worldwide. Effectiveness of tazobactam/piperacillin (TAZ/PIPC) in aspiration pneumonia is not clear.

PURPOSE

To compare clinical efficacy between TAZ/PIPC (1:4 compound) and imipenem/cilastatin (IPM/CS) in patients with moderate-to-severe aspiration pneumonia.

PATIENTS AND METHODS

In this open-label, randomized study either TAZ/PIPC 5 g or IPM/CS 1 g was intravenously administered every 12 h to patients with moderate-to-severe community-acquired aspiration pneumonia or nursing home-acquired pneumonia with risk for aspiration pneumonia for average 11 days. The primary outcome was clinical response rate at the end of treatment (EOT) in validated per-protocol (VPP) population. Secondary outcomes were clinical response during treatment (days 4 and 7) and at the end of study (EOS) in VPP population, and survival at day 30 in modified intention-to-treat (MITT) population.

RESULTS

There was no difference between the groups in primary or secondary outcome. However, significantly faster improvement as measured by axillary temperature (p < 0.05) and WBC count (p = 0.01) was observed under TAZ/PIPC treatment. In patients with gram-positive bacterial infection, TAZ/PIPC was more effective at EOT in VPP population (p = 0.03).

CONCLUSION

TAZ/PIPC is as effective and safe as IPM/CS in the treatment of moderate- to-severe aspiration pneumonia.

Pharmacokinetics of penicillin antibiotics: intravenous-to-oral switch therapy

Penicilinski antibiotiki delujejo baktericidno in spadajo med časovno odvisne antibiotike. Za večino penicilinov je značilna kratka razpolovna doba eliminacije. Benzilpenicilini se po peroralni aplikaciji ne absorbirajo, ampicilin in kloksacilin se sicer absorbirata, vendar slabo, medtem ko se amoksicilin skoraj v celoti absorbira. Pri slednjem je smotrno z intravenske terapije preklopiti na peroralno, če lahko s peroralno aplikacijo dosežemo plazemske koncentracije penicilina, primerljive s tistimi po intravenski aplikaciji, t. j. enako povprečno plazemsko koncentracijo penicilina v stacionarnem stanju. Posledično lahko pričakujemo enako učinkovitost obeh aplikacij. Smiselnost preklopne terapije je treba proučiti predvsem s stališča bolnika, saj ni primerna za bolnike, ki so v kritičnem stanju in imajo močno zvišano telesno temperaturo ali malabsorbcijski sindrom. Prednost preklopne terapije pa je v tem, da zmanjša pojavnost flebitisa in seps. V članku sta obravnavana dva primera preklopne terapije. Na osnovi farmakokinetičnih simulacij in indeksov učinkovitosti protibakterijskega zdravljenja je pokazana primerljivost intravenske terapije z ampicilinom in peroralne terapije z amoksicilinom, medtem ko preklopna terapija pri zdravljenju osteomielitisa s kloksacilinom ostaja nedorečena. Na podlagi predstavljenih primerov članek ilustrativno prikazuje, da ustrezna razlaga farmakokinetičnih parametrov bistveno pripomore k pravočasnemu preklopu z intravenske na peroralno terapijo s penicilinom. Takšna terapija je bolniku bolj prijazna, poleg tega pa prispeva k zniževanju stroškov za zdravljenje z zdravili v bolnišnicah ob še vedno varni in učinkoviti farmakoterapiji bakterijskih okužb.

Identification of optimal renal dosage adjustments for traditional and extended-infusion piperacillin-tazobactam dosing regimens in hospitalized patients

This study examined the effect of various levels of renal impairment on the probability of achieving free drug concentrations that exceed the MIC for 50% of the dosing interval (50% fT > MIC) for traditional and extended-infusion piperacillin-tazobactam (TZP) dosing strategies. It also identified optimal renal dosage adjustments for traditional and extended-infusion dosing schemes that yielded probability of target attainment (PTA) and exposure profiles that were isometric to those of the parent regimens. Data from 105 patients were analyzed using the population pharmacokinetic modeling program BigNPAG. To assess the effect of creatinine clearance (CL(CR)) on overall clearance, TZP clearance was made proportional to the estimated CL(CR). A Monte Carlo simulation (9,999 subjects) was performed for the traditional dosing scheme (4.5 g infused during 30 min every 6 h) and the extended-infusion TZP dosing scheme (3.375 g infused during 4 h every 8 h). The fraction of simulated subjects who achieved 50% fT > MIC was calculated for the range of piperacillin MICs from 0.25 to 32 mg/liter and stratified by CL(CR). The traditional TZP regimen displayed the greatest variability in PTA across MIC values, especially for MIC values exceeding 4 mg/liter, when stratified by CL(CR). In contrast, the PTA for the extended-infusion TZP regimen exceeded >or=80% for MIC values of or=32 mg/liter irrespective of the CL(CR). The CL(CR) adjustments for traditional and extended-infusion TZP dosing regimens should be considered at a CL(CR) of Collapse

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MESH Headings

• Area Under Curve
• Bayes Theorem
• Cross Infection/drug therapy
• Cross Infection/microbiology
• Drug Combinations
• Female
• Hospitalization
• Humans
• Infusions, Intravenous
• Kidney/metabolism
• Kidney Function Tests
• Male
• Microbial Sensitivity Tests
• Middle Aged
• Models, Statistical
• Monte Carlo Method
• Penicillanic Acid/administration & dosage
• Penicillanic Acid/analogs & derivatives
• Penicillanic Acid/pharmacokinetics
• Piperacillin/administration & dosage
• Piperacillin/pharmacokinetics
• Piperacillin, Tazobactam Drug Combination
• Pneumonia, Pneumococcal/drug therapy
• Pneumonia, Pneumococcal/microbiology
• Reproducibility of Results
• Tazobactam
• United States
• United States Food and Drug Administration

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Grants Collapse

Affiliation(s)

N. Patel Albany College of Pharmacy and Health Sciences, Albany, New York, Midwestern College of Pharmacy, Department of Pharmacy Practice, Downers Grove, Illinois, Northwestern Memorial Hospital, Department of Pharmacy, Chicago, Illinois, Ordway Research Institute, Albany, New York
M. H. Scheetz Albany College of Pharmacy and Health Sciences, Albany, New York, Midwestern College of Pharmacy, Department of Pharmacy Practice, Downers Grove, Illinois, Northwestern Memorial Hospital, Department of Pharmacy, Chicago, Illinois, Ordway Research Institute, Albany, New York
G. L. Drusano Albany College of Pharmacy and Health Sciences, Albany, New York, Midwestern College of Pharmacy, Department of Pharmacy Practice, Downers Grove, Illinois, Northwestern Memorial Hospital, Department of Pharmacy, Chicago, Illinois, Ordway Research Institute, Albany, New York
T. P. Lodise Albany College of Pharmacy and Health Sciences, Albany, New York, Midwestern College of Pharmacy, Department of Pharmacy Practice, Downers Grove, Illinois, Northwestern Memorial Hospital, Department of Pharmacy, Chicago, Illinois, Ordway Research Institute, Albany, New York

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Steady-state pharmacokinetics and pharmacodynamics of piperacillin/tazobactam administered by prolonged infusion in hospitalised patients

The objective of this study was to evaluate the steady-state pharmacokinetics and pharmacodynamics of piperacillin/tazobactam, administered by prolonged infusion, in hospitalised patients requiring antimicrobial therapy. Thirteen patients received 4.5 g every 8 h (q8h), infused over 4 h, and pharmacokinetic parameters were determined by non-compartmental methods. Monte Carlo simulations (10,000 patients) were performed to calculate the cumulative fraction of response (CFR) for seven gram-negative pathogens using minimum inhibitory concentration (MIC) data from the Meropenem Yearly Susceptibility Test Information Collection (2004-2007, USA) as well as the probability of target attainment (PTA) at MICs ranging from 1 microg/mL to 64 microg/mL. The pharmacodynamic target was free piperacillin concentration remaining above the MIC for 50% of the dosing interval. Mean+/-standard deviation maximum and minimum serum concentrations, half-life, volume of distribution at steady-state and systemic clearance of piperacillin were 108.2+/-31.7 microg/mL, 27.6+/-26.3 microg/mL, 2.1+/-1.2 h, 22.1+/-4.0 L and 8.6+/-3.0 L/h, respectively. The CFR was > 90% for Escherichia coli, Serratia marcescens and Citrobacter spp., 88.6% for Enterobacter spp., 87% for Klebsiella pneumoniae, 85.5% for Pseudomonas aeruginosa and 52.8% for Acinetobacter spp. The PTA was 100%, 81.1% and 12.3% at MICs of < or = 16 microg/mL, 32 microg/mL and 64 microg/mL, respectively. Piperacillin/tazobactam 4.5 g q8h infused over 4 h provides excellent target attainment for bacterial pathogens with MICs < or = 16 microg/mL. However, the CFR was < 90% for four of the seven gram-negative pathogens evaluated.

Comparison of the Pharmacokinetics of Piperacillin and Sulbactam during Intermittent and Continuous Intravenous Infusion

BACKGROUND

The antibacterial effect of piperacillin/sulbactam depends on the time of drug concentration above the minimal inhibitory concentration (MIC). Therefore, continuous infusion (CI) may be a more rational approach than standard intermittent short-term infusion (SI). The study investigated whether CI achieves effective drug concentrations comparable with SI.

METHODS

Seven intensive care unit patients received either piperacillin/sulbactam as 4/1 g intravenous infusion over 15-20 min every 8 h or as 4/1 g intravenous loading dose (15-20 min) followed by 8/2 g intravenous CI per 24 h. After 2 days, regimes were crossed over.

RESULTS

Pharmacokinetic parameters (mean +/- SD) for SI piperacillin/sulbactam were: (1) peak serum concentration: piperacillin 231 +/- 66 mg/l, sulbactam 53.1 +/- 15.0 mg/l; (2) minimum serum concentration: piperacillin 11.5 +/- 14.8 mg/l, sulbactam 4.2 +/- 3.5 mg/l; (3) clearance: piperacillin 197 +/- 72 ml/min (CI 269 +/- 123 ml/min), sulbactam 167 +/- 61 ml/min (CI 212 +/- 109 ml/min); (4) half-life: piperacillin 2.4 +/- 1.2 h, sulbactam 3.1 +/- 1.6 h. Steady-state concentrations during CI were 25.5 +/- 14.5 mg/l for piperacillin and 8.0 +/- 3.7 mg/l for sulbactam. Average serum concentrations were comparable in both regimens.

CONCLUSION

A large German survey demonstrated that approximately 89% of Pseudomonas aerugionsa have an MIC < or =16 mg/l and approximately 82% have an MIC < or =8 mg/l. According to this threshold, appropriate anti-bacterial concentrations of piperacillin/sulbactam were achievable with CI. CI dosing has the additional advantage that less drug is necessary. Further prospective studies are warranted to compare the clinical efficacy of CI and SI regimens in bacterial infections.

Pharmacodynamic profiling of piperacillin in the presence of tazobactam in patients through the use of population pharmacokinetic models and Monte Carlo simulation

The primary objectives of this analysis were to determine which pharmacokinetic model most accurately describes the elimination pathways for piperacillin in the presence of tazobactam through population pharmacokinetic modeling and to characterize its pharmacodynamic profile. Once the optimal pharmacokinetic model was identified, Monte Carlo simulation of 10,000 subjects with ADAPT II was performed to estimate the probability of attaining a target free-piperacillin concentration greater than the MIC for 50% of the dosing interval for 3.375 g every 6 h or every 4 h given as a 0.5-h infusion at each MIC between 0.25 and 32 microg/ml. In the population pharmacokinetic analysis, measurements of bias and precision, observed-predicted plots, and r2 values were highly acceptable for all three models and all three models were appropriate candidates for the Monte Carlo simulation evaluation. Visual comparison of the distribution of the piperacillin concentrations at the pharmacodynamic endpoint--h 3 concentrations of a 6-h dosing interval--between the simulated populations and raw data revealed that the linear model was most reflective of the raw data at the pharmacodynamic endpoint, and the linear model was therefore selected for the target attainment analysis. In the target attainment analysis, administration of 3 g of piperacillin every 6 h resulted in a robust target attainment rate that exceeded 95% for MICs of < or =8 mg/liter. The 4-h piperacillin administration interval had a superior pharmacodynamic profile and provided target attainment rates exceeding 95% for MICs of < or =16 mg/liter. This study indicates that piperacillin-tazobactam should have utility for empirical therapy of hospital-onset infections.

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

The OPTAMA Program is intended to examine typical antimicrobial regimens used in the treatment of common nosocomial pathogens and the likelihood of these regimens attaining appropriate pharmacodynamic exposure in different parts of the world. A 5,000-subject Monte Carlo simulation was used to estimate pharmacodynamic target attainment for meropenem, imipenem, ceftazidime, cefepime, piperacillin-tazobactam, and ciprofloxacin against Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa. Standard dosing regimens from North America were used. Pharmacokinetic parameter variability was derived from existing healthy volunteer data, and MIC data came from the 2002 MYSTIC Program. Ciprofloxacin displayed the lowest target attainment against all bacterial species (41 to 46% for A. baumannii, 53 to 59% for P. aeruginosa, and 80 to 85% for the Enterobacteriaceae). Increasing the dose to 400 mg every 8 h did not significantly increase target attainment against nonfermenters. Piperacillin-tazobactam target attainments were similar to that of ceftazidime against all pathogens. Higher doses of both compounds were needed to achieve better target attainments against P. aeruginosa. Overall, meropenem, imipenem, and cefepime attained the highest probabilities of attainment against the Enterobacteriaceae (99 to 100%). The carbapenems appear to be the most useful agents against A. baumannii (88 to 92%), and these agents, along with higher doses of any of the beta-lactams, would be the most appropriate choices for empirical therapy for P. aeruginosa infection. Given the lack of agreement between percent susceptibility and probability of target attainment for certain antimicrobial regimens, a methodology employing stochastic pharmacodynamic analyses may be a more useful tool for differentiating the most-optimal compounds and dosing regimens in the clinical setting of initial empirical therapy.

Pharmacodynamics of Meropenem and Imipenem Against Enterobacteriaceae,Acinetobacter baumannii, andPseudomonas aeruginosa

STUDY OBJECTIVE

To compare the pharmacodynamics of meropenem and imipenem, both administered as 500 mg every 6 hours, against populations of Enterobacteriaceae, Acinetobacter baumannii, and Pseudomonas aeruginosa.

DESIGN

Ten thousand-subject Monte Carlo simulation.

INTERVENTION

Variability in total body clearance (ClT), volume of distribution as calculated by the terminal elimination rate (Vdbeta), and minimum inhibitory concentration (MIC) distributions (Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Serratia marcescens, A. baumannii, P. aeruginosa) were derived from the literature for both meropenem and imipenem. For the free drug concentrations, the percentage of the dosing interval that the drug concentrations remain above the MIC (%T>MIC) for each carbapenem-bacteria combination was calculated for 10,000 iterations, substituting a different ClT, Vdbeta, fraction of unbound drug, and MIC into the equation each time based on the probability distribution for each parameter. Probabilities of attaining targets of 30%, 50%, and 100% T>MIC were calculated.

MEASUREMENTS AND MAIN RESULTS

Meropenem free drug %T>MIC exposure was significantly greater than that of imipenem against Enterobacteriaceae and P. aeruginosa, whereas imipenem exposure was greater for A. baumannii. For both agents, free drug %T>MIC exposure was greatest against Enterobacteriaceae and less for A. baumannii and P. aeruginosa. Probabilities of target attainment for 30% and 50% T>MIC were similar between drugs for most bacteria. At 100% T>MIC, meropenem target attainments were greater than those of imipenem against Enterobacteriaceae and P. aeruginosa, and imipenem attainment was higher for A. baumannii.

CONCLUSION

The probability of attaining lower pharmacodynamic targets for most gram-negative bacteria is similar for these carbapenems; however, differences become apparent as the pharmacodynamic requirement increases. Further study of the benefits of achieving this pharmacodynamic breakpoint with a higher probability of attaining targets is necessary.