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

Clinical Pharmacokinetics and Pharmacodynamics of Cefepime

Cefepime is a broad-spectrum fourth-generation cephalosporin with activity against Gram-positive and Gram-negative pathogens. It is generally administered as an infusion over 30-60 min or as a prolonged infusion with infusion times from 3 h to continuous administration. Cefepime is widely distributed in biological fluids and tissues with an average volume of distribution of ~ 0.2 L/kg in healthy adults with normal renal function. Protein binding is relatively low (20%), and elimination is mainly renal. About 85% of the dose is excreted unchanged in the urine, with an elimination half-life of 2-2.3 h. The pharmacokinetics of cefepime is altered under certain pathophysiological conditions, resulting in high inter-individual variability in cefepime volume of distribution and clearance, which poses challenges for population dosing approaches. Consequently, therapeutic drug monitoring of cefepime may be beneficial in certain patients including those who are critically ill, have life-threatening infections, or are infected with more resistant pathogens. Cefepime is generally safe and efficacious, with a goal exposure target of 70% time of the free drug concentration over the minimum inhibitory concentration for clinical efficacy. In recent years, reports of neurotoxicity have increased, specifically in patients with impaired renal function. This review summarizes the pharmacokinetics, pharmacodynamics, and toxicodynamics of cefepime contemporarily in the setting of increasing cefepime exposures. We explore the potential benefits of extended or continuous infusions and therapeutic drug monitoring in special populations.

β-lactam dosing strategies: Think before you push

OBJECTIVES

There has been interest in administering cefepime, a β-lactam antibiotic, via intravenous push (IVP) as a means to improve time to first-dose antibiotic and reduce cost; however, the downstream impacts on antibiotic exposure and pharmacodynamic efficacy need to be further evaluated.

METHODS

This study used a population pharmacokinetic model for cefepime and simulated exposures to predict the pharmacodynamic (PD) effect for cefepime regimens administered via IVP or 30-minute intermittent infusion in adults with different renal functions. FDA-approved adult dosages of 1-2 g every 8 or 12 hours were compared. This study aimed to compare the absolute difference in pharmacodynamic probability of target attainment (PTA) between IVP and intermittent infusion, defined as free cefepime concentrations above organism MIC for ≥ 70% of the time.

RESULTS

At MICs of 0.25-0.5 mg/L, absolute differences in PTA were observed, with a reduction as great as 2.3% (89% to 86.7% for 30-minute intermittent infusion and IVP, respectively). At MICs of 1-4 mg/L, 30-minute intermittent infusion and IVP exhibited PTA differences as great as 5.4%, from 89.4% to 84%, respectively. At MICs of ≥8 mg/L, similar absolute differences existed; however, no regimen achieved a PTA >70%. Across renal function strata of 60, 100 and 140 mL/minute (within the same dosing group and MICs), better renal function lowered PTAs.

CONCLUSIONS

Simulations demonstrated that IVP cefepime resulted in lower PTAs than traditional intermittent infusion among a subset of elevated MICs. Clinicians should exercise caution in IVP strategy, as unintended clinical consequences are possible.

Fluoroquinolone Versus Nonfluoroquinolone Treatment of Bloodstream Infections Caused by Chromosomally Mediated AmpC-Producing Enterobacteriaceae

Objectives: Chromosomally mediated AmpC-producing Enterobacteriaceae (CAE) display high susceptibility to fluoroquinolones; minimal clinical data exist supporting comparative clinical outcomes. The objective of this study was to compare treatment outcomes between fluoroquinolone and nonfluoroquinolone definitive therapy of bloodstream infections caused by CAE. Methods: This retrospective cohort assessed adult patients with positive blood cultures for CAE that received inpatient treatment for ≥48 h. The primary outcome was difference in clinical failure between patients who received fluoroquinolone (FQ) versus non-FQ treatment. Secondary endpoints included microbiological cure, infection-related length of stay, 90-day readmission, and all-cause inpatient mortality. Results: 56 patients were included in the study (31 (55%) received a FQ as definitive therapy; 25 (45%) received non-FQ). All non-FQ patients received a beta-lactam (BL). Clinical failure occurred in 10 (18%) patients, with 4 (13%) in the FQ group and 6 (24%) in the BL group (p = 0.315). Microbiological cure occurred in 55 (98%) patients. Median infection-related length of stay was 10 (6–20) days, with a significantly longer stay occurring in the BL group (p = 0.002). There was no statistical difference in 90-day readmissions between groups (7% FQ vs. 17% BL; p = 0.387); one patient expired. Conclusion: These results suggest that fluoroquinolones do not adversely impact clinical outcomes in patients with CAE. When alternatives to beta-lactam therapy are needed, fluoroquinolones may provide an effective option.

Evaluation of Dose-Fractionated Polymyxin B on Acute Kidney Injury Using a Translational In Vivo Rat Model

We investigated dose-fractionated polymyxin B (PB) on acute kidney injury (AKI). PB at 12 mg of drug/kg of body weight per day (once, twice, and thrice daily) was administered in rats over 72 h. The thrice-daily group demonstrated the highest KIM-1 increase (P = 0.018) versus that of the controls (P = 0.99) and histopathological damage (P = 0.013). A three-compartment model best described the data (bias, 0.129 mg/liter; imprecision, 0.729 mg2/liter2; R2, 0.652,). Area under the concentration-time curve at 24 h (AUC24) values were similar (P = 0.87). The thrice-daily dosing scheme resulted in the most PB-associated AKI in a rat model.

Development of Population and Bayesian Models for Applied Use in Patients Receiving Cefepime

BACKGROUND AND OBJECTIVE

Understanding pharmacokinetic disposition of cefepime, a β-lactam antibiotic, is crucial for developing regimens to achieve optimal exposure and improved clinical outcomes. This study sought to develop and evaluate a unified population pharmacokinetic model in both pediatric and adult patients receiving cefepime treatment.

METHODS

Multiple physiologically relevant models were fit to pediatric and adult subject data. To evaluate the final model performance, a withheld group of 12 pediatric patients and two separate adult populations were assessed.

RESULTS

Seventy subjects with a total of 604 cefepime concentrations were included in this study. All adults (n = 34) on average weighed 82.7 kg and displayed a mean creatinine clearance of 106.7 mL/min. All pediatric subjects (n = 36) had mean weight and creatinine clearance of 16.0 kg and 195.6 mL/min, respectively. A covariate-adjusted two-compartment model described the observed concentrations well (population model R², 87.0%; Bayesian model R², 96.5%). In the evaluation subsets, the model performed similarly well (population R², 84.0%; Bayesian R², 90.2%).

CONCLUSION

The identified model serves well for population dosing and as a Bayesian prior for precision dosing.

Clinical Impact of Revised Cefepime Breakpoint in Patients With Enterobacteriaceae Bacteremia

The impact of the revised Clinical and Laboratory Standards Institute interpretative criteria for cefepime in Enterobacteriaceae remains unclear. We applied the new breakpoint on 644 previously defined cefepime-susceptible Enterobacteriaceae isolates. We found no differences in mortality or microbiological failure, regardless of isolates being susceptible or cefepime-susceptible dose-dependent by current criteria.

A Translational Pharmacokinetic Rat Model of Cerebral Spinal Fluid and Plasma Concentrations of Cefepime

This study defines the transit of cefepime between plasma and cerebral spinal fluid (CSF) in a rat model. Male Sprague-Dawley rats received cefepime intravenously. Plasma samples were obtained via a second dedicated intravenous catheter. CSF sampling occurred via an intracisternal catheter. Drug exposures and transfer from the plasma to the CSF during the first 24 h were calculated. The median CSF/blood percentage of penetration was 19%. Cefepime transit to the CSF is rapid and predictable in the rat model. This model will be highly useful for understanding the therapeutic window for cefepime and neurotoxicity.

This study sought to define the transit of cefepime between plasma and cerebral spinal fluid (CSF) in a rat model. Male Sprague-Dawley rats received cefepime intravenously. A total daily dose of 150 mg/kg of body weight/day was administered as a single injection every 24 h for 4 days. Plasma samples were obtained via a second dedicated intravenous catheter. CSF sampling occurred via an intracisternal catheter. Cefepime levels in plasma and CSF were quantified via liquid chromatography-tandem mass spectrometry (LC-MS/MS). Pharmacokinetic (PK) analyses were conducted using Pmetrics for R. PK parameters and exposures during the first 24 h (i.e., area under the concentration-time curve from 0 to 24 h [AUC_0–24] and maximum concentration of drug in serum from 0 to 24 h [C_{max 0–24}]) were calculated from Bayesian posteriors. CSF penetration was estimated by comparing the exposure profiles between plasma and the CSF. Eleven rats contributed PK data. A four-compartmental model with a lag compartment for CSF fit the data well for both plasma (Bayesian [R² = 0.956]) and CSF (Bayesian [R² = 0.565]). Median parameter values (with the coefficient of variation percentage [CV%] in parentheses) for the rate constants to CSF from the lag compartment (K₃₄), to the central compartment from the CSF compartment (K₄₁), and to the lag compartment from the central compartment (K₁₃) were 2.96 h⁻¹ (116.27%), 0.47 h⁻¹ (54.86%), and 0.13 h⁻¹ (23.42%), respectively. The elimination rate constant (k_el) was 3.15 h⁻¹ (7.5%). Exposure estimation revealed a plasma median (with interquartile range [IQR] in parentheses) half-life, AUC_0–24, and C_{max 0–24}, of 1.7 (1.5 to 1.9) h, 111.3 (95.7 to 136.5) mg · 24 h/liter, and 177.8 (169.7 to 236.4) μg/ml, from the first dose, respectively. Exposure estimation of CSF demonstrated a median (with IQR in parentheses) AUC_0–24 and C_{max 0–24} of 26.3 (16.6 to 43.1) mg · 24 h/liter and 6.8 (5.2 to 9.4) μg/ml, respectively. The median CSF/blood percentage of penetration was 19%. Cefepime transit to the CSF is rapid and predictable in the rat model. This model will be highly useful for understanding the therapeutic window for cefepime and neurotoxicity.

IMPORTANCE This study defines the transit of cefepime between plasma and cerebral spinal fluid (CSF) in a rat model. Male Sprague-Dawley rats received cefepime intravenously. Plasma samples were obtained via a second dedicated intravenous catheter. CSF sampling occurred via an intracisternal catheter. Drug exposures and transfer from the plasma to the CSF during the first 24 h were calculated. The median CSF/blood percentage of penetration was 19%. Cefepime transit to the CSF is rapid and predictable in the rat model. This model will be highly useful for understanding the therapeutic window for cefepime and neurotoxicity.

Time for Precision: A World Without Susceptibility Breakpoints

Interpretive criteria for in vitro susceptibility testing criteria, "susceptibility breakpoints," underpin the evaluation and selection of antimicrobial regimens. However, despite their strengths, susceptibility breakpoints are a relatively blunt instrument employed to address an extremely complex question-what is the likelihood of treatment success for individual patients? With regard to evaluating patients on a case-by-case basis, breakpoints merely allow us to account for pathogen susceptibility. This approach precludes consideration of drug exposures achieved in patients, thus overlooking half of the equation for predicting treatment success. Herein, we propose the framework for considering both pathogen- and patient-specific information to provide clinicians a means of evaluating antimicrobial regimens for individual patients through tools automating pharmacokinetic-pharmacodynamic target attainment analyses. Implementing these tools along with their acceptance by professional organizations will allow for a shift in the paradigm for how antimicrobials are selected and dosed-toward patient-centered care through precision medicine.

Quantifying the importance of active antimicrobial therapy among patients with Gram-negative bloodstream infections: Cefepime as a representative agent

The quantitative importance of active antimicrobial treatment relative to other modifiable and non-modifiable risk factors for mortality has not been well defined in the literature. Here we quantify the impact of active antimicrobial treatment on mortality relative to other disease modifiers in patients with Gram-negative bloodstream infection (GNBSI). Patients with at least one positive blood culture who were treated with ≥24 h of cefepime for GNBSI were included in the study. To examine in-hospital survival, a full primary model and a base model with the least significant covariate from the primary model were established. Relative importance of covariates was calculated using percentages of difference in log-likelihood values when each covariate was iteratively added to the base model. A total of 154 unique patients with GNBSI were included. The primary model included active cefepime therapy (P = 0.004), normalised days to positive culture (P = 0.091), intensive care unit (ICU) at time of treatment (P = 0.001), modified Acute Physiology and Chronic Health Evaluation (APACHE) II score on day zero (P = 0.025), history of leukaemia (P = 0.008) and prior immunosuppressive therapy (P = 0.088). Active antimicrobial therapy displayed a relative importance of 32.2%, which was second to ICU residence at the time of culture. Amongst all covariates in the model, active antimicrobial therapy was the only modifiable variable and contributed significantly to in-hospital survival in acutely ill patients with GNBSI.

The Inoculum Effect in the Era of Multidrug Resistance: Minor Differences in Inoculum Have Dramatic Effect on MIC Determination

The observed MIC may depend on the number of bacteria initially inoculated into the assay. This phenomenon is termed the inoculum effect (IE) and is often most pronounced for β-lactams in strains expressing β-lactamase enzymes. The Clinical and Laboratory Standards Institute (CLSI)-recommended inoculum is 5 × 10⁵ CFU ml^-1 with an acceptable range of 2 × 10⁵ to 8 × 10⁵ CFU ml^-1 IE testing is typically performed using an inoculum 100-fold greater than the CLSI-recommended inoculum. Therefore, it remains unknown whether the IE influences MICs during testing performed according to CLSI guidelines. Here, we utilized inkjet printing technology to test the IE on cefepime, meropenem, and ceftazidime-avibactam. First, we determined that the inkjet dispense volume correlated well with the number of bacteria delivered to microwells in 2-fold (R² = 0.99) or 1.1-fold (R² = 0.98) serial dilutions. We then quantified the IE by dispensing orthogonal titrations of bacterial cells and antibiotics. For cefepime-resistant and susceptible dose-dependent strains, a 2-fold increase in inoculum resulted in a 1.6 log₂-fold increase in MIC. For carbapenemase-producing strains, each 2-fold reduction in inoculum resulted in a 1.26 log₂-fold reduction in meropenem MIC. At the lower end of the CLSI-allowable inoculum range, minor error rates of 34.8% were observed for meropenem when testing a resistant-strain set. Ceftazidime-avibactam was not subject to an appreciable IE. Our results suggest that IE is sufficiently pronounced for meropenem and cefepime in multidrug-resistant Gram-negative pathogens to affect categorical interpretations during standard laboratory testing.

Defining the impact of severity of illness on time above the MIC threshold for cefepime in Gram-negative bacteraemia: a 'Goldilocks' window

The quantitative impact of severity of illness on pharmacodynamic thresholds is poorly defined. We used a robust cefepime outcomes cohort and previously identified pharmacodynamic breakpoints of 68% [pharmacokinetic (PK) model 1] and 74% (PK model 2) to probe interactions and relationships with modified Acute Physiology and Chronic Health Evaluation (mAPACHE) II scores. When the time that serum concentration remains above the minimum inhibitory concentration during the dosing interval (fT_>MIC) was optimised, mortality was improved between mAPACHE II scores of 9-23 and 9-22 in models 1 and 2, respectively. No significant interactions were identified. These results suggest that mAPACHE II scores of 9-22 may fall within a 'Goldilocks' window in which hospital survival is improved among patients achieving goal fT_>MIC thresholds.

A propensity score-matched analysis of the impact of minimum inhibitory concentration on mortality in patients with Pseudomonas aeruginosa bacteremia treated with cefepime or ceftazidime

The United States Clinical and Laboratory Standards Institute recently elected not to revise ceftazidime and cefepime Pseudomonas aeruginosa minimum inhibitory concentration (MIC) susceptibility breakpoints but rather recommended specific dosage regimens to correspond to breakpoints. This study's objective was to examine mortality of low and high MIC P. aeruginosa isolates in bacteremic patients treated with cefepime or ceftazidime. Data were gathered through a Veterans Health Administration national administrative database for veterans with P. aeruginosa blood cultures who received cefepime or ceftazidime. Seventy-four patients in the low MIC (≤2 μg/mL) group and 29 patients in the high (4-8 μg/mL) MIC group were included. Independent baseline variables associated with 30-day all-cause mortality were determined through multivariate analysis to calculate propensity scores and perform matching. All-cause 30-day mortality was not statistically significant between the 2 resultant propensity score-matched groups (17.2% mortality in the low MIC group versus 27.6% in the high MIC group; P=0.34). Data suggested that P. aeruginosa bacteremia episodes where the cephalosporin MIC = 8 μg/mL may have higher mortality, however this may be reflective of higher propensity scores. Our study suggests that it is reasonable to designate a cefepime or ceftazidime MIC ≤8 μg/mL as susceptible for P. aeruginosa bacteremia infections, but potential suboptimal outcomes in episodes for which the P. aeruginosa MIC is 8 μg/mL may need further investigation.

Updates in the Management of Cephalosporin-Resistant Gram-Negative Bacteria

Resistance to cephalosporins is now common among Gram-negative bacterial infections, including those caused by the Enterobacteriaceae and Pseudomonas aeruginosa, posing a major threat to public health. As resistance to the traditional drugs of choice for these infections, carbapenems, has also become increasingly common, interest in cefepime and piperacillin-tazobactam as carbapenem-sparing alternatives has increased. Additionally, the availability of the novel β-lactam-β-lactamase inhibitor combinations ceftolozane-tazobactam and ceftazidime-avibactam has added to the antimicrobial armamentarium available to treat these multidrug-resistant infections. Here, we review the recent literature on the use of carbapenem-sparing alternatives and highlight the potential utility of novel antimicrobials.

Pediatric extended spectrum β-lactamase infection: Community-acquired infection and treatment options

BACKGROUND

Infection caused by extended spectrum β-lactamase (ESBL)-producing Enterobacteriaceae in pediatric patients has been increasing and spreading to the community, compromising the options for effective antibiotics. This retrospective study was conducted to identify which antibiotics ESBL-producing Enterobacteriaceae remain susceptible to. In addition, the prevalence of community-acquired infection caused by these organisms, and the possibility of association between these organisms and septic shock, were explored.

METHODS

Antibiotic susceptibility of ESBL-producing and non-ESBL-producing Escherichia coli and Klebsiella pneumoniae strains isolated from pediatric patients were reviewed to determine the rates of susceptibility to various antibiotics. A chart review was performed to clarify the prevalence of community-acquired infection and the severity.

RESULTS

Of 849 strains analyzed, 40% were ESBL positive. Apart from cephalosporins, ESBL-producing strains were also less likely to be susceptible to other antibiotics, such as quinolones, gentamicin, netilmicin, and cotrimoxazole, more than 90% of which were still susceptible to amikacin, carbapenems, colistin, and tigecycline. Around 20% of community-acquired infections in the present study were caused by ESBL-producing strains. ESBL-producing strains found in the community were more likely to be susceptible to gentamicin, netilmicin, and cefepime than those found in hospital. Infection caused by ESBL-producing strains was not significantly associated with septic shock.

CONCLUSION

The increase in infection caused by ESBL-producing Enterobacteriaceae limits the availability of effective antibiotics. Given that carbapenems are necessary for treating serious infections, amikacin, cefepime, and piperacillin/tazobactam are possible options for consolidative therapy or for non-serious infection.

Impact of CLSI Breakpoint Changes on Microbiology Laboratories and Antimicrobial Stewardship Programs

In 2010, the Clinical and Laboratory Standards Institute (CLSI) lowered the MIC breakpoints for many beta-lactam antibiotics to enhance detection of known resistance amongEnterobacteriaceae The decision to implement these new breakpoints, including the changes announced in both 2010 and 2014, can have a significant impact on both microbiology laboratories and antimicrobial stewardship programs. In this commentary, we discuss the changes and how implementation of these updated CLSI breakpoints requires partnership between antimicrobial stewardship programs and the microbiology laboratory, including data on the impact that the changes had on antibiotic usage at our own institution.

Defining Clinical Exposures of Cefepime for Gram-Negative Bloodstream Infections That Are Associated with Improved Survival

The percentage of time that free drug concentrations remain above the MIC (fT>MIC) that is necessary to prevent mortality among cefepime-treated patients with Gram-negative bloodstream infections (GNBSI) is poorly defined. We conducted a retrospective study of adult patients with GNBSI. Eligible cases were frequency matched to ensure categorical representation from all MICs. Organism, MIC, infection source, gender, age, serum creatinine, weight, antibiotic history, and modified APACHE II score were collected from hospital records. Two population pharmacokinetic models (models 1 and 2) were used to impute exposures over the first 24 h in each patient from mean model parameters, covariates, and dosing history. From the imputed exposures, survival thresholds for fT>MIC were identified using classification and regression tree (CART) analysis and analyzed as nominal variables for univariate and multivariate regressions. A total of 180 patients were included in the analysis, of whom 13.9% died and 86.1% survived. Many patients (46.7% [n = 84/180]) received combination therapy with cefepime. Survivors had higher mean (standard deviation [SD]) fT>MIC than those who died (model 1, 74.2% [29.6%] versus 52.1% [33.8%], P < 0.001; model 2, 85.9% [24.0%] versus 64.4% [31.4%], P < 0.001). CART identified fT>MIC threshold values for greater survival according to models 1 and 2 at >68% and >74%, respectively. Survival was improved for those with fT>MIC of >68% (model 1 adjusted odds ratio [aOR], 7.12; 95% confidence interval [CI], 1.90 to 26.7; P = 0.004) and >74% (model 2 aOR, 6.48; 95% CI, 1.90 to 22.1) after controlling for clinical covariates. Similarly, each 1% increase in cefepime fT>MIC resulted in a 2% improvement in multivariate survival probability (P = 0.015). Achieving a cefepime fT>MIC of 68 to 74% was associated with a higher odds of survival for patients with GNBSI. Regimens targeting this exposure should be aggressively pursued.

Tree-Based Models for Predicting Mortality in Gram-Negative Bacteremia: Avoid Putting the CART before the Horse

Increasingly, infectious disease studies employ tree-based approaches, e.g., classification and regression tree modeling, to identify clinical thresholds. We present tree-based-model-derived thresholds along with their measures of uncertainty. We explored individual and pooled clinical cohorts of bacteremic patients to identify modified acute physiology and chronic health evaluation (II) (m-APACHE-II) score mortality thresholds using a tree-based approach. Predictive performance measures for each candidate threshold were calculated. Candidate thresholds were examined according to binary logistic regression probabilities of the primary outcome, correct classification predictive matrices, and receiver operating characteristic curves. Three individual cohorts comprising a total of 235 patients were studied. Within the pooled cohort, the mean (± standard deviation) m-APACHE-II score was 13.6 ± 5.3, with an in-hospital mortality of 16.6%. The probability of death was greater at higher m-APACHE II scores in only one of three cohorts (odds ratio for cohort 1 [OR1] = 1.15, 95% confidence interval [CI] = 0.99 to 1.34; OR2 = 1.04, 95% CI = 0.94 to 1.16; OR3 = 1.18, 95% CI = 1.02 to 1.38) and was greater at higher scores within the pooled cohort (OR4 = 1.11, 95% CI = 1.04 to 1.19). In contrast, tree-based models overcame power constraints and identified m-APACHE-II thresholds for mortality in two of three cohorts (P = 0.02, 0.1, and 0.008) and the pooled cohort (P = 0.001). Predictive performance at each threshold was highly variable among cohorts. The selection of any one predictive threshold value resulted in fixed sensitivity and specificity. Tree-based models increased power and identified threshold values from continuous predictor variables; however, sample size and data distributions influenced the identified thresholds. The provision of predictive matrices or graphical displays of predicted probabilities within infectious disease studies can improve the interpretation of tree-based model-derived thresholds.