Does the piperacillin minimum inhibitory concentration for Pseudomonas aeruginosa influence clinical outcomes of children with pseudomonal bacteremia?

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.

Clinical characteristics and risk factors for mortality in children with Pseudomonas aeruginosa bacteraemia: A retrospective review at a paediatric tertiary centre

AIM

The objective of this study was to describe clinical features and to assess the risk factors associated with mortality in Pseudomonas aeruginosa bacteraemia in a tertiary Japanese paediatric care hospital.

METHODS

Patients diagnosed with P. aeruginosa bacteraemia at our hospital between 2007 and 2018 were analysed in a retrospective case series. Inadequate initial therapy for P. aeruginosa bacteraemia was defined as initial treatment without antipseudomonal antibiotics or an administration of antipseudomonal agent to which the causative strain was resistant. Bacteraemia-related death was defined as all deaths occurring within 7 days after the onset of bacteraemia.

RESULTS

Overall, 41 patients with 42 P. aeruginosa bacteraemia episodes were identified. The most common underlying condition was malignancy (27%), followed by congenital heart disease (20%) and preterm birth (17%). Among the 42 P. aeruginosa clinical isolates, 24% were resistant to at least one of the antipseudomonal agents and 10% were resistant to more than one agent. The susceptibility levels for piperacillin, fourth-generation cephalosporins and ciprofloxacin were higher than that for carbapenems. Bacteraemia-related death was observed in 43% of episodes. The 30-day all-cause mortality was 50% (standard error 8%). Neonates, intensive care, mechanical ventilation, afebrile episodes, septic shock, hypoxia, renal injury and inadequate initial therapy were associated with bacteraemia-related death episodes.

CONCLUSIONS

We found that childhood P. aeruginosa bacteraemia is still a high mortality disease. Our results imply the importance of the identification of high-risk patients and the establishment of adequate empirical antibiotic therapy.

Pharmacokinetics of Antibiotics in Pediatric Intensive Care: Fostering Variability to Attain Precision Medicine

Children show important developmental and maturational changes, which may contribute greatly to pharmacokinetic (PK) variability observed in pediatric patients. These PK alterations are further enhanced by disease-related, non-maturational factors. Specific to the intensive care setting, such factors include critical illness, inflammatory status, augmented renal clearance (ARC), as well as therapeutic interventions (e.g., extracorporeal organ support systems or whole-body hypothermia [WBH]). This narrative review illustrates the relevance of both maturational and non-maturational changes in absorption, distribution, metabolism, and excretion (ADME) applied to antibiotics. It hereby provides a focused assessment of the available literature on the impact of critical illness—in general, and in specific subpopulations (ARC, extracorporeal organ support systems, WBH)—on PK and potential underexposure in children and neonates. Overall, literature discussing antibiotic PK alterations in pediatric intensive care is scarce. Most studies describe antibiotics commonly monitored in clinical practice such as vancomycin and aminoglycosides. Because of the large PK variability, therapeutic drug monitoring, further extended to other antibiotics, and integration of model-informed precision dosing in clinical practice are suggested to optimise antibiotic dose and exposure in each newborn, infant, or child during intensive care.

Comparison of piperacillin plasma concentrations in a prospective randomised trial of extended infusion versus intermittent bolus of piperacillin/tazobactam in paediatric patients

OBJECTIVES

To be effective, piperacillin/tazobactam (PTZ) unbound plasma levels need to be above the minimum inhibitory concentration (MIC) at least 50% of the time between dosing intervals (50% fT_>MIC). This study aimed to compare the plasma piperacillin concentrations at the mid-dosing intervals (C_mid, 50% fT) and the proportion of patients achieving 50% fT_>MIC between extended infusion (EI) and intermittent bolus (IB) methods in children.

METHODS

A prospective, randomised trial of EI versus IB of PTZ was conducted in children aged 1 month to 18 years. The PTZ dose was 100 mg/kg intravenously every 8 h. Patients were randomly assigned to receive EI (4-h infusion) or IB (30-min infusion). The primary outcome that was measured was plasma piperacillin C_mid.

RESULTS

Ninety patients with a median age (IQR) of 48 months (16-127) were enrolled. The most common indication for PTZ use was pneumonia (32.2%). Geometric mean (95% CI) plasma piperacillin C_mid of EI versus IB was 51.9 mg/L (40.6-66.6) versus 6.0 mg/L (4.2-8.6) (P < 0.01). The EI group had a trend of higher proportion of patients who achieved 50% fT_>4xMIC (72.7% versus 30.0%; P = 0.06).

CONCLUSIONS

PTZ administration with EI resulted in a higher C_mid compared with IB. In settings with increased piperacillin MICs, this approach should be implemented, particularly during the empirical treatment period.

Microbial findings, sensitivity and outcome in patients with postoperative peritonitis a retrospective cohort study

BACKGROUND

Acute postoperative peritonitis resulting from previous abdominal surgery is still a severe and potentially fatal disease, which is associated with high morbidity and mortality. The aim of the present study was to evaluate patients' outcome after postoperative peritonitis and identify the most effective empiric antibiotic regimes.

METHODS

422 patients with acute postoperative peritonitis as a result to earlier abdominal operation (e.g. anastomotic leakage) were analyzed retrospectively focusing on the origin of the peritonitis, microbial flora and resistance patterns. Furthermore, mortality was estimated according to sensitivity results of the tested antibiotics.

RESULTS

In 50% of the patients, anastomotic leakage was located in the colon. The predominantly cultured microorganisms were Escherichia coli and Enterobacteriaceae. The combination of meropenem and vancomycin was effective in 96% of these microbes. The frequently used combinations of piperacillin/sulbactam and cefotaxime/metronidazole were effective in only 67% and 43%, respectively.

CONCLUSIONS

We were able to show that the currently used antibiotic regimes with piperacillin/sulbactam and cefotaxime/metronidazole are ineffective in a relevant number of patients with anastomotic leakage. Only meropenem or meropenem/vancomycin cover most of the microbes predominant in postoperative peritonitis.

Pronounced activity of aromatic selenocyanates against multidrug resistant ESKAPE bacteria

Selenocyanates demonstrate pronounced activity against bacteria of the ESKAPE family, yeast and nematodes with limited cytotoxicity against human cells.

Anti-infective Acquisition Costs for a Stewardship Program: Getting to the Bottom Line

Background

Though antimicrobial stewardship programs (ASPs) are in place for patient safety, financial justification is often required. In 2016, the Infectious Diseases Society of America (IDSA) recommended that anti-infective costs be measured by patient-level administration data normalized for patient census. Few publications use this methodology. Here, we aim to compare 3 methods of drug cost analysis during 3 phases of an ASP as an example of this recommendation's implementation.

Methods

At a freestanding pediatric hospital, we retrospectively assessed anti-infective cost using pharmacy purchasing data, patient-level administration data from the electronic medical record (EMR), and patient-level administration data from the Pediatric Hospital Information Systems (PHIS) database, all normalized to patient census. Costs pre-ASP, while planning the ASP, and post-ASP were then compared for each method.

Results

Significant differences in costs between the methods were observed. Pharmacy purchasing endorsed minimal financial benefit (decrease planning to post-ASP of $590 dollars per 1000 patient-days), while the EMR and PHIS data endorsed a decrease of $12785 and $21380 per 1000 patient-days, respectively, for a total yearly cost savings of $54656 for pharmacy purchasing data, $1184336 for EMR data, and $2117522 for PHIS data.

Conclusions

Pharmacy purchasing data underestimated cost savings compared with EMR and PHIS data, while EMR and PHIS data were comparable in magnitude of savings. At Children's Hospital Colorado, savings justified the full cost of the ASP. EMR patient-level administration data, normalized to patient census, offers a readily available and standardized measure of anti-infective costs over time.

Ceftaroline for Suspected or Confirmed Invasive Methicillin-Resistant Staphylococcus aureus: A Pharmacokinetic Case Series

OBJECTIVES

To describe the ceftaroline pharmacokinetics in critically ill children treated for suspected or confirmed methicillin-resistant Staphylococcus aureus infections, including blood stream infection and describe the microbiological and clinical outcomes.

DESIGN

Retrospective electronic medical record review.

SETTINGS

Free-standing tertiary/quaternary pediatric children's hospital.

PATIENTS

Critically ill children receiving ceftaroline monotherapy or combination therapy for suspected or confirmed methicillin-resistant S. aureus infections in the PICU.

INTERVENTION

None.

MEASUREMENTS AND MAIN RESULTS

Seven patients, three females (43%), and four males (57%), accounted for 33 ceftaroline samples for therapeutic drug management. A median of four samples for therapeutic drug management was collected per patient (range, 2-9 samples). The median age was 7 years (range, 1-13 yr) with a median weight of 25.5 kg (range, 12.6-40.1 kg). Six of seven patients (86%) demonstrated an increase in volume of distribution, five of seven patients (71%) demonstrated an increase in clearance, and 100% of patients demonstrated a shorter half-life estimate as compared with the package insert estimate. Six of seven patients (85.7%) had documented methicillin-resistant S. aureus growth from a normally sterile site with five of six (83.3%) having documented BSI, allowing six total patients to be evaluated for the secondary objective of microbiological and clinical response. All six patients achieved a positive microbiological and clinical response for a response rate of 100%.

CONCLUSIONS

These data suggest the pharmacokinetics of ceftaroline in PICU patients is different than healthy pediatric and adult patients, most notably a faster clearance and larger volume of distribution. A higher mg/kg dose and a more frequent dosing interval for ceftaroline may be needed in PICU patients to provide appropriate pharmacodynamic exposures. Larger pharmacokinetic, pharmacodynamic, and interventional treatment trials in the PICU population are warranted.

Influence of borderline cefepime MIC on the outcome of cefepime-susceptible Pseudomonas aeruginosa bacteremia treated with a maximal cefepime dose: a hospital-based retrospective study

BACKGROUND

We assessed the influence of current cefepime minimal inhibitory concentration (MIC) breakpoints and the maximal cefepime dose on treatment outcomes in patients with bacteremia caused by cefepime-susceptible Pseudomonas aeruginosa.

METHODS

Adult patients hospitalized between July 2010 and June 2014 with a positive blood culture for cefepime-susceptible P. aeruginosa and receipt of cefepime as the primary therapy throughout the course were reviewed. Cefepime Etest^® MICs and clinical outcomes for P. aeruginosa bacteremia were reviewed to identify the MIC breakpoint influencing treatment outcomes.

RESULTS

Of the 90 patients enrolled, 49 (54.4%) were male (mean age = 66.8 years). The mean Acute Physiology and Chronic Health Evaluation II score was 22.01. Sixty patients (66.7%) received a maximal cefepime dose, and the 30-day crude mortality rate was 36.7%. MIC₉₀ of cefepime for P. aeruginosa was 8 mg/L. The cumulative survival rate at 30 days revealed that a lower cefepime MIC (<4 mg/L) for P. aeruginosa was associated with a higher survival rate than a higher MIC (≥4 mg/L) (72.6% vs. 23.5%, p < 0.0001). A cefepime MIC of ≥4 mg/L and age were independent risk factors for mortality, whereas the maximal cefepime dose was the independent protective factor. The use of a maximal cefepime dose did not improve the outcomes of patients with P. aeruginosa bacteremia at a MIC of ≥4 mg/L.

CONCLUSIONS

A cefepime MIC of 4 mg/L may predict an unfavorable outcome among patients with serious infections caused by P. aeruginosa, even the MICs still within the CLSI susceptibility breakpoint.

Continuous and Prolonged Intravenous β-Lactam Dosing: Implications for the Clinical Laboratory

Beta-lactam antibiotics serve as a cornerstone in the management of bacterial infections because of their wide spectrum of activity and low toxicity. Since resistance rates among bacteria are continuously on the rise and the pipeline for new antibiotics does not meet this trend, an optimization of current beta-lactam treatment is needed. This review provides an overview of optimization through use of prolonged- and continuous-infusion dosing strategies compared with more traditional intermittent infusions. Included is an overview of the scientific basis for using these nontraditional prolonged- and continuous-infusion-based regimens, with a focus on major areas in which the clinical laboratory can support the clinical use of these regimens.

A propensity score-matched analysis of the impact of minimum inhibitory concentration on mortality in patients with Pseudomonas aeruginosa bacteraemia treated with piperacillin/tazobactam

The Clinical and Laboratory Standards Institute (CLSI) recently re-examined Pseudomonas aeruginosa minimum inhibitory concentration (MIC) susceptibility breakpoints for piperacillin/tazobactam (TZP). The objectives of this study were to analyse the impact of elevated TZP MICs (32-64 mg/L) versus lower respective MICs on P. aeruginosa bacteraemia patient outcomes. Data were gathered from a Veterans Health Administration national clinical database on P. aeruginosa bacteraemia episodes from 2007 to 2013. Patients treated with TZP were identified, comprising 53 elevated MIC episodes and 301 low MIC episodes. Propensity score matching (1:2 ratio) utilising independent variables associated with 30-day all-cause mortality was conducted to compare the outcomes of 53 elevated MIC episodes with 106 matched low MIC episodes. Independent baseline variables associated with 30-day all-cause mortality for all 354 episodes were hyperkalaemia, elevated blood urea nitrogen, elevated temperature, hypoglycaemia, lack of urinary source and thrombocytopenia. Similar 30-day all-cause mortality was found between the two propensity-matched TZP groups (elevated MIC 24.5% vs. low MIC 22.6%; P = 0.79).

Population Pharmacokinetic Analysis of Piperacillin/Tazobactam in Korean Patients with Acute Infections

Background

For more effective and safer usage of antibiotics, the dosing strategy should be individualized based on the patients’ characteristics, including race. The aim of this study was to investigate the population pharmacokinetic (PK) profiles of piperacillin and tazobactam in Korean patients with acute infections.

Materials and Methods

At least four consecutive 2/0.25 g or 4/0.5 g doses of piperacillin/tazobactam (TZP) were intravenously infused over 1 h every 8 h for patients with creatinine clearance (CL_cr) ≤50 ml/min or CL_cr >50 mL/min, respectively. Blood samples from 33 patients at a steady-state were taken pre-dose and at 0 min, 30 min, and 4-6 h after the fourth infusion. The population PK analysis was conducted using a non-linear mixed-effects method. A likelihood ratio test was used to select significant covariates, with significance levels of P <0.05 for selection and P <0.01 for elimination.

Results

Both piperacillin PK and tazobactam PK were well described by a two-compartment model with first-order elimination. Creatinine clearance and body weight, as covariates on clearance (CL) and volume of central compartment (V1), were selected among the covariates possibly affecting PK parameters of both drugs. CL was defined as CL = 2.9 + 4.03 × CL_cr /47 for piperacillin and CL = 1.76 + 4.81 × CL_cr /47 for tazobactam. V1 was defined as V1 = 19.5 × weight/60 for piperacillin and V1 = 22.6 × weight/60 for tazobactam.

Conclusion

The PK profiles of TZP at a steady-state in Korean patients with acute infections were well described by a two-compartment model with first-order elimination. Both piperacillin and tazobactam clearances were significantly influenced by creatinine clearance.

Targeted benefits of prolonged-infusion piperacillin-tazobactam in an in vitro infection model of Pseudomonas aeruginosa

Given the inconsistent clinical findings, our goal was to characterize the pharmacodynamics (PDs) of prolonged-infusion piperacillin-tazobactam (TZP) in an in vitro pharmacodynamic model of Pseudomonas aeruginosa. Specifically, the study was designed to investigate the influence of MIC on the activity of prolonged-infusion TZP using pharmacokinetics (PKs) consistent with a non-critically ill patient population. There was no benefit with prolonged- compared with standard-infusion TZP against isolates with susceptible MICs of 8 or 16 mg/L. However, prolonged-infusion TZP produced more than two times the final bacterial kill against less susceptible isolates with an intermediate MIC of 32 mg/L. The PDs of TZP were well described by a sigmoid Emax model (r(2) = 0.84) where %ƒT>MIC thresholds of 27 and 75% were associated with bacteriostatic and bactericidal effects, respectively. However, the well-established PD relationship with %ƒT>MIC was not observed with prolonged-infusion TZP. In conclusion, this study characterizes the targeted benefits of prolong-infusion TZP based on pathogen MIC, and supports the assertion that the benefits are selective and most likely observed in patients with less susceptible pathogens or altered PKs.

Population Pharmacokinetics and Pharmacodynamics of Extended-Infusion Piperacillin and Tazobactam in Critically Ill Children

The study objective was to evaluate the population pharmacokinetics and pharmacodynamics of extended-infusion piperacillin-tazobactam in children hospitalized in an intensive care unit. Seventy-two serum samples were collected at steady state from 12 patients who received piperacillin-tazobactam at 100/12.5 mg/kg of body weight every 8 h infused over 4 h. Population pharmacokinetic analyses were performed using NONMEM, and Monte Carlo simulations were performed to estimate the piperacillin pharmacokinetic profiles for dosing regimens of 80 to 100 mg/kg of the piperacillin component given every 6 to 8 h and infused over 0.5, 3, or 4 h. The probability of target attainment (PTA) for a cumulative percentage of the dosing interval that the drug concentration exceeds the MIC under steady-state pharmacokinetic conditions (TMIC) of ≥50% was calculated at MICs ranging from 0.25 to 64 mg/liter. The mean ± standard deviation (SD) age, weight, and estimated glomerular filtration rate were 5 ± 3 years, 17 ± 6.2 kg, and 118 ± 41 ml/min/1.73 m(2), respectively. A one-compartment model with zero-order input and first-order elimination best fit the pharmacokinetic data for both drugs. Weight was significantly associated with piperacillin clearance, and weight and sex were significantly associated with tazobactam clearance. Pharmacokinetic parameters (mean ± SD) for piperacillin and tazobactam were as follows: clearance, 0.22 ± 0.07 and 0.19 ± 0.07 liter/h/kg, respectively; volume of distribution, 0.43 ± 0.16 and 0.37 ± 0.14 liter/kg, respectively. All extended-infusion regimens achieved PTAs of >90% at MICs of ≤16 mg/liter. Only the 3-h infusion regimens given every 6 h achieved PTAs of >90% at an MIC of 32 mg/liter. For susceptible bacterial pathogens, piperacillin-tazobactam doses of ≥80/10 mg/kg given every 8 h and infused over 4 h achieve adequate pharmacodynamic exposures in critically ill children.

Impact of the MIC of piperacillin/tazobactam on the outcome for patients with bacteraemia due to Enterobacteriaceae: the Bacteraemia-MIC project

OBJECTIVE

Our objective was to evaluate the impact of low versus borderline MIC of piperacillin/tazobactam on the clinical outcomes of patients with bacteraemia caused by Enterobacteriaceae who were treated with that antimicrobial.

PATIENTS AND METHODS

A prospective observational multicentre cohort study was conducted in 13 Spanish university hospitals. Patients >17 years old with bacteraemia due to Enterobacteriaceae who received empirical piperacillin/tazobactam treatment for at least 48 h were included. Outcome variables were clinical response at day 21, clinical response at end of treatment with piperacillin/tazobactam and all-cause 30 day mortality. Univariate and multivariate logistic regression analyses were performed.

RESULTS

Overall, 275 patients were included in the analysis; 248 (90.2%) in the low MIC group (≤ 4 mg/L) and 27 (9.8%) in the borderline MIC group (8-16 mg/L). The biliary tract was the most common source of infection (48.4%) and Escherichia coli was the most frequent pathogen (63.3%). Crude 30 day mortality rates were 10.5% and 11.1% for the low MIC group and the borderline MIC group, respectively (relative risk = 1.06, 95% CI = 0.34-3.27, P = 1). Multivariate analysis of failure at day 21 and at end of treatment with piperacillin/tazobactam and 30 day mortality showed no trend towards increased clinical failure or mortality with borderline MICs (OR = 0.96, 95% CI = 0.18-4.88, P = 0.96; OR = 0.47, 95% CI = 0.10-2.26, P = 0.35; OR = 1.48, 95% CI = 0.33-6.68, P = 0.6).

CONCLUSIONS

We did not find that higher piperacillin/tazobactam MIC within the susceptible or intermediate susceptibility range had a significant influence on the outcome for patients with bacteraemia due to Enterobacteriaceae.

Optimized antimicrobial dosing strategies: a survey of pediatric hospitals

BACKGROUND

Extended-interval aminoglycoside (EIAG) and extended- and continuous-infusion β-lactam (EIBL and CIBL) dosing strategies are increasingly used in adults, but pediatric literature is limited.

OBJECTIVE

The objective of this study was to describe the use of EIAG, EIBL, and CIBL dosing in pediatric hospitals in the USA.

STUDY DESIGN, SETTING, AND PARTICIPANTS

A national survey of children's hospitals was conducted. A single practitioner from each target hospital was identified through the Children's Hospital Association. Practice-based survey questions identified whether hospitals utilize EIAG, EIBL, and CIBL dosing.

MAIN OUTCOME MEASURE

The main outcome measure was the percentage utilization of the dosing strategies, with secondary outcomes being the reasons for not using these dosing strategies.

RESULTS

Seventy-seven of 215 identified practitioners (36 %) participated in the survey. EIAG, EIBL, and CIBL dosing were utilized in 63 %, 24 %, and 13 % of responding hospitals, respectively. The most common reasons for not using EIAG were concern regarding lack of efficacy data (56 %) and concern regarding the duration of the drug-free period (41 %). Respondents who did not utilize EIBL cited concern due to lack of pediatric EIBL efficacy data (54 %), the need for more intravenous access (54 %), intravenous medication compatibility issues (39 %), and the time during which the patient is attached to an intravenous infusion (31 %).

CONCLUSION

This survey of children's hospitals indicates that EIAG is used in over 50 % of hospitals, but there is some lag in adoption of EIBL and CIBL dosing, both of which are used in fewer than 25 % of hospitals. Additional studies may provide much-needed evidence to increase the utilization of these strategies.

Pharmacokinetic/pharmacodynamic modelling approaches in paediatric infectious diseases and immunology

Pharmacokinetic/pharmacodynamic (PKPD) modelling is used to describe and quantify dose-concentration-effect relationships. Within paediatric studies in infectious diseases and immunology these methods are often applied to developing guidance on appropriate dosing. In this paper, an introduction to the field of PKPD modelling is given, followed by a review of the PKPD studies that have been undertaken in paediatric infectious diseases and immunology. The main focus is on identifying the methodological approaches used to define the PKPD relationship in these studies. The major findings were that most studies of infectious diseases have developed a PK model and then used simulations to define a dose recommendation based on a pre-defined PD target, which may have been defined in adults or in vitro. For immunological studies much of the modelling has focused on either PK or PD, and since multiple drugs are usually used, delineating the relative contributions of each is challenging. The use of dynamical modelling of in vitro antibacterial studies, and paediatric HIV mechanistic PD models linked with the PK of all drugs, are emerging methods that should enhance PKPD-based recommendations in the future.

Developmental pharmacokinetics of piperacillin and tazobactam using plasma and dried blood spots from infants

Piperacillin-tazobactam is often given to infants with severe infection in spite of limited pharmacokinetics (PK) data. We evaluated piperacillin-tazobactam PK in premature and term infants of ages <61 days with suspected systemic infection. Infants received intravenous piperacillin-tazobactam (80 to 100 mg/kg of body weight every 8 h [q 8 h]) based on gestational and postnatal age. Sparse plasma samples were obtained after first and multiple doses. Drug concentrations were measured by tandem mass spectrometry. PK data were analyzed using population nonlinear mixed-effect modeling. Target attainment rates for the time unbound piperacillin concentrations remained above the MIC for 50% and 75% of the dosing interval at steady state were evaluated. Bias in population PK parameter estimates was assessed for dried blood spot (DBS) samples, and a comparability analysis was performed for DBS and plasma drug concentrations using linear regression. We obtained 128 plasma samples from 32 infants, median gestational age of 30 weeks (range, 23 to 40 weeks) and postnatal age of 8 days (range, 1 to 60). Piperacillin and tazobactam PK models included body weight (WT) and postmenstrual age (PMA) as covariates for clearance and WT for volume of distribution and were used to optimize dosing in infants. DBS drug concentrations were 50 to 60% lower than those in plasma, but when combined with plasma concentrations and a matrix effect, the data generated PK model parameters similar to those for plasma alone. With PMA-based dosing (100 mg/kg q 8 h, 80 mg/kg q 6 h, and 80 mg/kg q 4 h for PMA of ≤30, 30 to 35, and 35 to 49 weeks, respectively), 90% of simulated infants achieved the surrogate therapeutic target of time above the MIC (≤32 mg/liter) for 75% of the dosing interval.

Efficacy and safety of low-dose colistin in the treatment for infections caused by multidrug-resistant gram-negative bacteria

WHAT IS KNOWN AND OBJECTIVE

Infections due to multidrug-resistant gram-negative bacteria (MDR-GNB) are a significant burden to the healthcare system globally. Colistin is the drug of choice for MDR-GNB and recent studies recommend high doses. This study investigated the safety of low-dose colistin and the relationship of minimum inhibitory concentration (MIC) of colistin with bacterial cure in the treatment for MDR-GNB infections.

METHODS

Computerized dispensing records identified all patients who received colistin during January 2010 and December 2011. Patients who were aged < 12 years old, who received colistin for < 72 h or had moderate to severe renal impairment were excluded. Medical records of the remaining patients were reviewed for the necessary data to determine the bacterial cure and nephrotoxicity of colistin. Multivariate logistic regression analysis was used to determine the predictors of bacterial cure.

RESULTS

A total of 125 evaluable patients received colistin during the study period. Ninety-four of 125 (75·2%) patients achieved bacterial cure. No statistically significant differences were observed between patients who achieved and failed to achieve bacterial cure with regards to age, gender, site of infection, mg/kg dose or duration of colistin use. The average MIC in the bacterial cure group was significantly lower than the MIC in the bacterial failure group (P = 0·002). Similarly, 30-day mortality from the last dose of colistin was significantly lower in the bacterial cure group (P = 0·002). Nephrotoxicity occurred in 12·8% of patients and was not associated with the dose of colistin or concomitant use of nephrotoxic medications. MIC of <1 μg/mL was the only significant independent predictor of bacterial cure in the multivariate logistic regression analysis (P = 0·015), whereas infection caused by MDR Klebsiella pneumonia was an independent risk factor for bacterial failure (P = 0·049).

WHAT IS NEW AND CONCLUSION

Low-dose colistin is an effective option in the treatment for infections caused by MDR-GNB with a low incidence of nephrotoxicity. Patients who achieved bacterial cure had significantly lower MIC values of colistin against MDR-GNB than those who failed to achieve it. Colistin dose should be based on the MIC data of a given patient or local antimicrobial sensitivity data to maximize its efficacy.

Less is more: combination antibiotic therapy for the treatment of gram-negative bacteremia in pediatric patients

IMPORTANCE

Definitive combination antibiotic therapy with a β-lactam and an aminoglycoside for the treatment of gram-negative bacteremia is commonly prescribed in pediatric patients; however, its efficacy and toxicity relative to β-lactam monotherapy are unknown.

OBJECTIVE

To determine whether definitive combination antibiotic therapy affects mortality and nephrotoxicity in pediatric patients with gram-negative bacteremia.

DESIGN, SETTING, AND PARTICIPANTS

Retrospective cohort study including pediatric patients (aged ≤18 years) with gram-negative bacteremia hospitalized at the Johns Hopkins Children's Center between 2002 and 2011.

MAIN OUTCOMES AND MEASURES

Outcomes included 30-day mortality and nephrotoxicity classified according to the pediatric RIFLE (risk for renal dysfunction, injury to the kidney, failure of kidney function, loss of kidney function, and end-stage renal disease) criteria. To account for nonrandom assignment of combination therapy, propensity score weighting was combined with multivariable logistic regression to estimate the effect of combination therapy on mortality and nephrotoxicity.

RESULTS

Of the 879 eligible pediatric patients with bacteremia, 537 (61.1%) received combination therapy. After propensity score adjustment, baseline demographic and clinical characteristics between the groups were well balanced. There was no association between combination therapy and 30-day mortality (odds ratio, 0.98; 95% CI, 0.93-1.02; P = .27). There were 170 patients (19.3%) with evidence of acute kidney injury, including 135 (25.1%) and 35 (10.2%) in the combination therapy and monotherapy arms, respectively. Patients receiving combination therapy had approximately twice the odds of nephrotoxicity compared with those receiving monotherapy (odds ratio, 2.15; 95% CI, 2.09-2.21).

CONCLUSIONS AND RELEVANCE

The use of β-lactam monotherapy for gram-negative bacteremia in pediatric patients reduces subsequent nephrotoxicity without compromising survival.