Comparative pharmacokinetics, pharmacodynamics, and tolerability of ertapenem 1 gram/day administered as a rapid 5-minute infusion versus the standard 30-minute infusion in healthy adult volunteers

Outcomes of Intravenous Push versus Intermittent Infusion Administration of Cefepime in Critically Ill Patients

The equivalence of intravenous push (IVP) and piggyback (IVPB) administration has not been evaluated in the critically ill population for most medications, but it is especially relevant for antibiotics, such as cefepime, that exhibit time-dependent bactericidal activity. A single center, retrospective, observational pre/post-protocol change study included critically ill adults who received cefepime as empiric therapy between August 2015 and 2021. The primary outcome was treatment failure, which was defined as a composite of escalation of antibiotic regimen or all-cause mortality. Secondary outcomes included adverse drug events, days of cefepime therapy, total days of antibiotic therapy, and ICU and hospital length of stay. Outcomes were compared using Chi-squared, Mann Whitney U, and binary logistic regression as appropriate. A total of 285 patients were included: 87 IVPB and 198 IVP. Treatment failure occurred in 18% (n = 16) of the IVPB group and 27% (n = 54) of the IVP group (p = 0.109). There were no significant differences in secondary outcomes. Longer duration of antibiotics (odds ratio [OR] 1.057, 95% confidence interval [CI] 1.013-1.103), SOFA score (OR 1.269, 95% CI 1.154-1.397) and IVP administration of cefepime (OR 2.370, 95% CI 1.143-4.914) were independently associated with treatment failure. Critically ill patients who received IVP cefepime were more likely to experience treatment failure in an adjusted analysis. The current practice of IVP cefepime should be reevaluated, as it may not provide similar clinical outcomes in the critically ill population.

Pushing the agenda for intravenous push administration in outpatient parenteral antimicrobial therapy

Intravenous push (IVP) antimicrobial administration refers to rapid bolus infusion of medication. This drug delivery method offers improved patient convenience, superior patient and nursing satisfaction, and cost savings when used in outpatient parenteral antimicrobial therapy (OPAT). Antimicrobial agents must demonstrate optimal physiochemical and pharmacologic characteristics, as well as sufficient syringe stability, to be administered in this manner. Additionally, impacts on medication tolerability, patient safety, and effectiveness must be considered. This narrative review summarizes the available data and practical implications of IVP administration of antimicrobials in the OPAT setting.

Ertapenem Concentrations in Obese Patients Undergoing Surgery

Background: Antimicrobial prophylaxis is a cornerstone to preventing surgical site infections (SSIs). Ertapenem, a carbapenem antibiotic, is commonly used for surgical prophylaxis for many different procedures, including patients undergoing colorectal and other gastrointestinal surgeries. Obesity complicates surgical intervention and increases the risk for SSIs. This study aims to describe the pharmacokinetics of ertapenem for surgical prophylaxis using a population pharmacokinetic model. Patients and Methods: Ten patients were recruited and given a single dose of ertapenem 1 g intravenous over 30 minutes. Plasma samples were obtained at multiple time points over 24 hours and assayed via validated high-performance liquid chromatography (HPLC). Pharmacokinetic analyses were conducted using a population pharmacokinetic analysis to generate pharmacokinetic parameters used in the subsequent 5,000 patient Monte Carlo simulation. The probability of target attainment (PTA) for free drug concentrations remaining above the minimum inhibitory concentration (MIC) for ≥40% was used. Results: The mean maximum plasma concentration and area under the concentration time curve (AUC_0-∞) was 40.7 ± 16.5 and 148.8 ± 28.0, respectively, with a half-life of the terminal portion to be 4.3 ± 0.8 hours. Monte Carlo simulations observed PTAs above 90% for MICs ≤0.25 and ≤0.125 mcg/mL in surgeries up to three and four hours, respectively. Sufficiently high PTAs were not attainable for MICs of ≥0.5 mcg/mL. Conclusions: Ertapenem given as 1 g single dose may be an appropriate candidate for surgical prophylaxis in obese patients undergoing surgeries of four hours or less.

Is the Success of Cefazolin plus Ertapenem in Methicillin-Susceptible Staphylococcus aureus Bacteremia Based on Release of Interleukin 1-beta?

Cefazolin and ertapenem has been shown to be an effective salvage regimen for refractory methicillin-susceptible Staphylococcus aureus bacteremia. Our findings suggest cefazolin plus ertapenem in vitro stimulates interleukin-1β release from peripheral blood monocytes both with and without S. aureus presence. This IL-1β augmentation was primarily driven by ertapenem. These findings support further exploration of cefazolin plus ertapenem in MSSA bacteremia and may partially explain its marked potency in vivo despite modest synergy in vitro .

Safety of Intravenous Push Ertapenem Compared to Intravenous Piggyback at a Tertiary Academic Medical Center

Background: Recent shortages of intravenous (IV) fluids have resulted in healthcare systems converting administration of many medications from IV piggyback (IVPB) to IV push (IVP). Administering medications via IVP presents numerous advantages; however, IV site reactions such as phlebitis and infiltration may occur. Objective: The objective of this analysis is to evaluate the infusion site safety of ertapenem given as peripheral IVP compared to IVPB in adult patients. Methods: This was an institutional review board-approved, single-center, retrospective study. Patients, ages 18 or older, receiving IV ertapenem were identified. The major endpoints analyzed were IV site reactions including phlebitis and infiltration. The Naranjo Nomogram was utilized to assess the causality of the reactions to determine the likelihood of whether the event was caused by the medication itself or other factors. Results: To date, 283 administrations (92 patients) in the IVP group and 319 administrations (82 patients) in the IVPB group were analyzed. There were 13 IV site reactions compared to 8 in the IVP vs IVPB group, respectively (P-value = 0.16). Ten of the events in the IVP group were deemed "possible" and 2 deemed "doubtful," while the remaining event was considered "probable" per the Naranjo Nomogram. Of the events in the IVPB group, all 8 were found to be "possible." Conclusion: The administration of IVP ertapenem showed comparable rates of infusion site reactions compared to IVPB. Implementation of IVP ertapenem appears to be associated with infusion site safety similar to IVPB and should be considered safe to administer.

Evaluation of First-Dose, Intravenous Push Penicillins and Carbapenems in the Emergency Department

BACKGROUND

Early appropriate antibiotic administration is associated with improved outcomes in infectious illnesses. During drug shortages in 2017, the American Society of Health-System Pharmacists recommended intravenous push (IVP) administration of medications when possible to conserve small-volume parenteral solutions. Data supporting IVP penicillins and carbapenems was limited.

OBJECTIVE

The primary objective of this study compared time from patient emergency department (ED) arrival to antibiotic administration between IVP and intravenous piggy-back (IVPB) administration.

METHODS

This single-center pre-post protocol study assessed changes in administration timing and safety of ampicillin/sulbactam, piperacillin/tazobactam, and ertapenem from 2015-2018. Medication administration by IVPB (pre) or IVP (post), ED arrival, antibiotic order and administration times, potential effectors of administration time, and safety events were assessed. Acquisition costs were estimated.

RESULTS

A total of 696 administrations were included, with 351 and 345 subjects in the IVPB and IVP cohorts, respectively. The median time from ED arrival to initiation of antibiotic administration was 140 (IQR 87-221) minutes and 110 (IQR 68-181) minutes in the IVPB and IVP cohorts, respectively, (P < 0.01). IVP administration increased the proportion of indexed antibiotics administered within 60 minutes of ED arrival compared to IVPB (20% vs. 12%, respectively, P < 0.01). There was no difference in adverse events between both cohorts. Supply acquisition cost savings totaled an more than $5,000 with the IVP protocol.

CONCLUSION

IVP administration of ampicillin/sulbactam, piperacillin/tazobactam, and ertapenem improved times to initiation of empiric, first-dose antibiotics in the ED without an increase in adverse events, saving over $5,000 annually.

Intravenous push versus intravenous piggyback beta-lactams for the empiric management of gram-negative bacteremia

WHAT IS KNOWN AND OBJECTIVE

Nationwide shortages of small-volume parenteral solutions (SVPS) compelled hospitals to develop strategies including the use of intravenous push (IVP) administration of antibiotics to reserve SVPS for absolute necessities. It is unknown if administration of beta-lactam antibiotics (BL) via IVP results in worse clinical outcomes compared to intravenous piggyback (IVPB) due to the potential inability to achieve pharmacodynamic targets.

METHODS

Our health-system implemented a mandatory IVP action plan for BL from October 2017 to September 2018. This was a retrospective study of adult patients with GNB who received empiric therapy with IVPB (30 minutes) or IVP (5 minutes) cefepime (FEP) or meropenem (MEM) for at least 2 days. Endpoints included clinical response, microbiological clearance and mortality. All data are presented as n (%) or median (interquartile range).

RESULTS

The final cohort included 213 patients (IVPB n = 105, IVP n = 108). The primary source of bacteremia was urinary, with Escherichia coli being the primary pathogen. Escalation of therapy was similar between groups (15 [14%] vs 11 [10%], P = .36) at a median of 3 days (P = .68). No significant differences were observed in any secondary endpoints including microbiological clearance, bacteremia recurrence, time to defervescence, WBC normalization, vasopressor duration or in-hospital mortality.

WHAT IS NEW AND CONCLUSION

Our findings suggest no differences in clinical response with the use of IVP compared to IVPB FEP and MEM for treatment of GNB. This form of administration may be considered as a fluid conservation strategy in times of shortage.

Safety and tolerability of i.v. push piperacillin/tazobactam within an emergency department

PURPOSE

Piperacillin/tazobactam is a broad-spectrum antibiotic that is widely used and commonly administered via the intravenous (i.v.) piggyback route over 0.5 to 4.0 hours. Recommendations for i.v. push (IVP) administration of piperacillin/tazobactam are lacking due to the high osmolality of the solution. The primary objective of this study was to retrospectively assess the safety and tolerability of piperacillin/tazobactam administered peripherally by IVP. Methods. A retrospective chart review was conducted to evaluate adverse drug reactions after administration of a single dose of IVP piperacillin/tazobactam through a peripheral line in an emergency department from August 2016 through November 2017.

RESULTS

A total of 1,813 patients received 1 dose of IVP piperacillin/tazobactam during the study timeframe. Three hundred patients were randomly selected for assessment of safety and tolerability. Two hundred ninety-nine patients (99.7%) tolerated IVP piperacillin/tazobactam. One patient had an allergic reaction that included itching and hives. No infusion-related reactions were documented.

CONCLUSION

IVP administration of piperacillin/tazobactam through a peripheral site is safe and tolerable for adult patients.

Safety of intravenous push administration of beta-lactams within a healthcare system

PURPOSE

A critical shortage of small-volume parenteral solutions in late 2017 led hospitals to develop strategies to ensure availability for critical patients, including administration of antibiotics as intravenous push (IVP). Minimal literature has been published to date that assesses the safety of administration of beta-lactams via this route. Therefore, the purpose of this study was to evaluate the safety of IVP administration of select beta-lactam antibiotics.

METHODS

We performed a retrospective review of IVP administrations of aztreonam, ceftriaxone, cefepime, and meropenem at two campuses of the New York University Langone Health system after October 2017. Patients receiving surgical prophylaxis or more than one IVP antibiotic simultaneously were excluded. The primary endpoint was adverse events (ADE) following IVP administration of antibiotics.

RESULTS

We evaluated 1000 patients who received IVP aztreonam (n = 43), ceftriaxone (n = 544), cefepime (n = 368) or meropenem (n = 45). There were 10 (1%) ADE observed, 5 of which were allergic reactions. Four ADE were neurotoxicity related to IVP cefepime. Based on the Naranjo score, 1 adverse event was "probably" and 3 were "possibly" related to cefepime IVP administration. Lastly, only 1 report of phlebitis was observed with the use of IVP ceftriaxone.

CONCLUSIONS

The use of IVP as an alternative to intravenous piggyback (IVPB) during times of drug shortage for select beta-lactam antibiotics appears to be safe, and ADE are similar to those previously described for IVPB administration. Future studies evaluating clinical outcomes between IVP and IVPB administration may be of benefit.

Pharmacokinetics of Ertapenem in Sheep (Ovis aries) with Experimentally Induced Urinary Tract Infection

Sheep are commonly used as animal models for human biomedical research, but descriptions of their use for studying the pharmacokinetics of carbapenem antimicrobials, such as ertapenem, are unavailable. Ertapenem is a critical antimicrobial for human infections, and the description of the pharmacokinetics of this drug is of value for research using ovine as models for human diseases, such as urinary tract infections (UTI). There are currently no ovine models for comparative biomedical research of UTI. The objective of this study was to report the pharmacokinetics of ertapenem in sheep after single and multiple dosing. In addition, we explored the effects of an immunomodulatory drug (Zelnate) on the pharmacokinetics of ertapenem in sheep. Eight healthy ewes (weight, 64.4 ± 7.7 kg) were used in an ovine bacterial cystitis model of human cystitis with Pseudomonas aeruginosa. After disease confirmation, each ewe received 1 g of ertapenem intravenously once every 24 h for 5 administrations. Blood was collected intensively (14 samples) during 24 h after the first and last administration. After multiple-dose administration, the volume of distribution was 84.5 mL/kg, clearance was 116.3 mL/h/kg, T1/2₍λ_z) was 1.1 h, and the extraction ratio was 0.02. No significant differences in pharmacokinetic parameters or time points were found between groups treated with the immunostimulant and controls or after the 1st or 5th administration of ertapenem. No accumulation was noted from previous administration. Our ovine pharmacokinetic findings can be used to evaluate therapeutic strategies for ertapenem use (varying drug dosing schedules and combinations with other antimicrobials or immune modulators) in the context of UTI.

Effects of i.v. push administration on β-lactam pharmacodynamics

PURPOSE

The effects of i.v. push administration on the pharmacodynamic exposures of meropenem, cefepime, and aztreonam were evaluated.

METHODS

Pharmacokinetic and pharmacodynamic analyses were conducted using previously published pharmacokinetic data for meropenem, cefepime, and aztreonam. The probability of target attainment (PTA) was assessed using Monte Carlo simulations for 30-minute and 5-minute infusions of approved dosing regimens and alternative dosing schemes often used in clinical practice, including 500 mg every 6 hours and 1 g every 8 hours for meropenem, 1 g every 6 hours and 2 g every 8 hours for cefepime, and 2 g every 8 hours for aztreonam. For each regimen examined, means and standard deviations for the percentage of the dosing interval that the free drug concentration remained above the minimum inhibitory concentration (MIC) were calculated and reported.

RESULTS

No or only minor differences were noted between 30-minute and 5-minute infusions. The largest differences were observed at an MIC of 4 mg/L for meropenem and an MIC of 16 mg/L for aztreonam. At an MIC of 4 mg/L, meropenem 500 mg every 6 hours as a 30-minute infusion had an 8% greater PTA compared with the 5-minute infusion. At an MIC of 16 mg/L, a 30-minute infusion of aztreonam 2 g every 8 hours had a 12% greater PTA compared with the 5-minute infusion.

CONCLUSION

Simulations of meropenem, cefepime, and aztreonam by i.v. push over 5 minutes indicated that there would be minimal or no effect on pharmacodynamic exposures compared with the effect when administered by 30-minute infusions.

Pharmacokinetic-Pharmacodynamic Evaluation of Ertapenem for Patients with Hospital-Acquired or Ventilator-Associated Bacterial Pneumonia

Ertapenem provides activity against many pathogens commonly associated with hospital-acquired and ventilator-associated bacterial pneumoniae (HABP and VABP, respectively), including methicillin-susceptible Staphylococcus aureus and numerous Gram-negative pathogens with one major gap in coverage, Pseudomonas aeruginosa Pharmacokinetic-pharmacodynamic (PK-PD) target attainment analyses were conducted to evaluate ertapenem against the most prevalent Enterobacteriaceae causing HABP/VABP. The objective of these analyses was to provide dose selection support for and demonstrate the appropriateness of ertapenem to empirically treat patients with HABP/VABP when administered with murepavadin, a novel targeted antimicrobial exhibiting a highly specific spectrum of activity against P. aeruginosa A previously developed population pharmacokinetic model, a total-drug epithelial lining fluid (ELF) to free-drug serum penetration ratio, contemporary in vitro surveillance data for ertapenem against Enterobacteriaceae, and percentage of the dosing interval for which drug concentrations exceed the MIC value (%T>MIC) targets associated with efficacy were used to conduct Monte Carlo simulations for five ertapenem regimens administered over short or prolonged durations of infusion. Overall total-drug ELF percent probabilities of PK-PD target attainment based on a %T>MIC target of 35% among simulated patients with HABP/VABP arising from Enterobacteriaceae based on pathogen prevalence data for nosocomial pneumonia ranged from 89.1 to 92.7% for all five ertapenem regimens evaluated. Total-drug ELF percent probabilities of PK-PD target attainment ranged from 99.8 to 100%, 97.9 to 100%, 10.6 to 74.1%, and 0 to 1.50% at MIC values of 0.06, 0.12, 1, and 4 μg/ml, respectively (MIC₉₀ values for Escherichia coli, Serratia marcescens, Enterobacter species, and Klebsiella pneumoniae, respectively). Results of these analyses provide support for the evaluation of ertapenem in combination with murepavadin for the treatment of patients with HABP/VABP.

Optimal infusion rate in antimicrobial therapy explosion of evidence in the last five years

Background

Sporadic studies in antimicrobial therapy have evaluated the effects of infusion rates on therapeutic and economic outcomes, and new findings may challenge the regular infusion regimen.

Methods

Focusing on studies comparing the outcomes of different infusion regimens, the relevant literature was identified by searching PubMed, Web of Science, and Scopus from January 1, 2013 to March 1, 2018. Papers were finally chosen using a PRISMA flowchart.

Results

Antimicrobials with the superiority of prolonged infusion to standard infusion in terms of efficacy and safety include meropenem, doripenem, imipenem, cefepime, ceftazidime, piperacillin/tazobactam, linezolid, and vancomycin. The strategy of concomitantly reducing total daily dose and prolonging infusion time may cause treatment failure (eg, imipenem). Extended infusion of piperacillin/tazobactam has pharmacoeconomic advantage over standard infusion. Prolonged infusion of voriconazole is inferior to standard infusion because of lower efficacy caused by pharmacokinetic changes. Comparable outcomes following standard infusion and continuous infusion were observed with norvancomycin and nafcillin. Factors determining whether prolonged infusion has a benefit over standard infusion include MIC of bacterial pathogens, bacterial density, diagnosis, disease severity, total daily dose, and renal function.

Conclusion

To maximally preserve the effectiveness of current antimicrobials, effective interventions should be implemented to enhance the application of optimal infusion strategies. For reducing nephrotoxicity, prolonged infusion of meropenem is better than conventional infusion in neonates with Gram-negative late-onset sepsis, and continuous infusion of vancomycin is superior to intermittent infusion. For increasing efficacy, prolonged or continuous infusion of time-dependent antimicrobials (eg, meropenem, doripenem, imipenem, cefepime, ceftazidime, piperacillin/tazobactam, linezolid, and vancomycin) is an optimal choice. Nevertheless, such advantages may only be demonstrated in special clinical circumstances and special populations (eg, patients with a sequential organ failure assessment (SOFA) score≥9, respiratory tract infections, urinary or intra-abdominal infections, or infections caused by less susceptible pathogens would benefit from prolonged infusion of piperacillin/tazobactam).

Intravenous Push Administration of Antibiotics: Literature and Considerations

Intravenous (IV) push administration can provide clinical and practical advantages over longer IV infusions in multiple clinical scenarios, including in the emergency department, in fluid-restricted patients, and when supplies of diluents are limited. In these settings, conversion to IV push administration may provide a solution. This review compiles available data on IV push administration of antibiotics in adults, including preparation, stability, and administration instructions. Prescribing information, multiple tertiary drug resources, and primary literature were consulted to compile relevant data. Several antibiotics are Food and Drug Administration-approved for IV push administration, including many beta-lactams. In addition, cefepime, ceftriaxone, ertapenem, gentamicin, and tobramycin have primary literature data to support IV push administration. While amikacin, ciprofloxacin, imipenem/cilastatin, and metronidazole have limited primary literature data on IV push administration, available data do not support that route. In addition, a discussion on practical considerations, such as IV push best practices and pharmacodynamic considerations, is provided.

Field Wound Care: Prophylactic Antibiotics

Adequate management of wounds requires numerous interventions, one of which is the appropriate use of antimicrobials to attempt to minimize the risk of excess morbidity or mortality without increasing toxicity or multidrug resistant bacterial acquisition. There are numerous recommendations and opinions for not only the use of systemic prophylactic antimicrobials, but also the agent, dose, route, and duration. To best address the implementation of systemic antimicrobials in a field scenario, one must weigh the factors that go into that decision and then determine the best agents possible. The epidemiologic triangle (ie, the host, the agent, and the environment) forms the basis for selecting the correct prophylactic antibiotic for field wound care. Extreme conditions can be encountered in both military and nonmilitary systems, requiring a unique selection process to make the right antibiotic choice. A modifiable weighted matrix, recommended previously for point of injury combat casualty care, assists in selecting the best oral and intravenous/intramuscular agent based on the epidemiologic risk determination.

Sterilizing Effect of Ertapenem-Clavulanate in a Hollow-Fiber Model of Tuberculosis and Implications on Clinical Dosing

Carbapenems are now being explored for treatment of multidrug-resistant tuberculosis (MDR-TB), especially in conjunction with clavulanate. Clinical use is constrained by the need for multiple parenteral doses per day and the lack of knowledge of the optimal dose for sterilizing effect. Our objective was to identify the ertapenem exposure associated with optimal sterilizing effect and then design a once-a-day dose for clinical use. We utilized the hollow-fiber system model of tuberculosis in a 28-day exposure-response study of 8 different ertapenem doses in combination with clavulanate. The systems were sampled at predetermined time points to verify the concentration-time profile and identify the total bacterial burden. Inhibitory sigmoid maximum-effect (E_max) modeling was used to identify the relationship between total bacterial burden and the drug exposure and to identify optimal exposures. Contrary to the literature, ertapenem-clavulanate combination demonstrated good microbial kill and sterilizing effect. In a dose fractionation hollow-fiber study, efficacy was linked to percentage of the 24-h dosing interval of ertapenem concentration persisting above MIC (%T_MIC). We performed 10,000 MDR-TB patient computer-aided clinical trial simulations, based on Monte Carlo methods, to identify the doses and schedule that would achieve or exceed a %T_MIC of ≥40%. We identified an intravenous dosage of 2 g once per day as achieving the target in 96% of patients. An ertapenem susceptibility breakpoint MIC of 2 mg/liter was identified for that dose. An ertapenem dosage of 2 g once daily is the most suitable to be tested in a phase II study of sterilizing effect in MDR-TB patients.

In vitro antibacterial activity of fosfomycin combined with other antimicrobials against KPC-producing Klebsiella pneumoniae

The increasing prevalence of KPC-producing Klebsiella pneumoniae (KPC-Kp) strains poses a serious threat to patients. Therapeutic options are limited to colistin, fosfomycin, tigecycline and selected aminoglycosides. Although the combination of fosfomycin with other antimicrobials is recommended, data regarding possible synergistic activity in vitro and in vivo appear inconsistent. Here we report that five drug combinations (fosfomycin combined with imipenem, ertapenem, tigecycline, colistin or amikacin) had a significant additive effect against 136 KPC-Kp strains in an in vitro chequerboard assay. In addition, time-kill assays revealed that fosfomycin enhanced the bactericidal activity of the five other antimicrobial agents. Moreover, owing to its persistent bactericidal effect, the combination of fosfomycin plus amikacin is an effective therapeutic candidate for infections by KPC-producing organisms.

A pharmacokinetic-pharmacodynamic model characterizing the emergence of resistant Escherichia coli subpopulations during ertapenem exposure

OBJECTIVES

Resistant subpopulations with reduced expression of outer membrane porins have been observed in ESBL-producing Escherichia coli during exposure to ertapenem. The aim of this work was to develop a pharmacokinetic-pharmacodynamic (PKPD) model to characterize the emergence of resistant E. coli during exposure to ertapenem and to predict bacterial killing following different dosing regimens of ertapenem.

METHODS

Data from in vitro time-kill experiments were used to develop a mechanism-based PKPD model for three E. coli strains: a native strain, an ESBL-producing strain, and an ESBL-producing strain with reduced expression of porins OmpF and OmpC. Each strain was exposed to static ertapenem concentrations (1-512 × MIC) for 24 h using starting inocula of ∼10(6) and 10(8) cfu/mL.

RESULTS

The developed PKPD model consisted of three bacterial states: susceptible growing, less susceptible non-growing, and non-susceptible non-growing bacteria. A pre-existing bacterial subpopulation was used to describe the emergence of resistance. The PKPD model adequately characterized the data of the three E. coli strains investigated. Results from predictions suggest that the conventional dosage (1 g intravenously once daily) might result in regrowth of resistant subpopulations when used to treat infection caused by ESBL-producing strains.

CONCLUSIONS

Resistant subpopulations frequently emerged in E. coli when exposed to ertapenem, supporting that the time course of emergence of resistance should be taken into consideration when selecting dosing regimens.

Stability of ertapenem 100 mg/mL in polypropylene syringes stored at 25, 4, and -20 °C

PURPOSE

The stability of ertapenem solution in syringes at room, refrigerator, and freezer temperatures was determined to establish options for extended storage.

METHODS

Six replicate solutions of ertapenem (100 mg/mL) in 0.9% sodium chloride injection were prepared in 20-mL polypropylene syringes and stored at 25, 4, or -20 °C. Syringe samples were collected immediately after preparation and at preselected time points and assayed by a validated high-performance liquid chromatography (HPLC) method. The ertapenem solution was considered stable if at least 90% of the mean initial concentration remained at the time of HPLC analysis.

RESULTS

The mean±S.D. baseline ertapenem concentration across all stability studies was 109.9±9.2 mg/mL. One hour after preparation, the mean±S.D. ertapenem concentration of samples kept at room temperature was 87.8±4.6% of the initial concentration. After 24 and 48 hours of refrigeration, mean±S.D. drug concentrations had declined to 93.6±5.9% and 86.2±4.3% of the respective baseline concentrations. Frozen syringes required 1 hour to thaw at room temperature; after 14 and 28 days of frozen storage, the mean±S.D. ertapenem concentrations of these samples 4 hours after thawing were 93.4±3.5% and 86.4±2.6% of the respective baseline values.

CONCLUSION

Ertapenem 100 mg/mL prepared in 20-mL polypropylene syringes was stable at room temperature for approximately 30 minutes. Room-temperature stability was extended to 4 hours after 24 hours of refrigeration. After being frozen for 14 or 28 days, ertapenem was stable for 3-5 hours after removal from the freezer.

β-Lactams enhance daptomycin activity against vancomycin-resistant Enterococcus faecalis and Enterococcus faecium in in vitro pharmacokinetic/pharmacodynamic models

Enterococcus faecalis and Enterococcus faecium are frequently resistant to vancomycin and β-lactams. In enterococcal infections with reduced glycopeptide susceptibility, combination therapy is often administered. Our objective was to conduct pharmacokinetic/pharmacodynamic (PK/PD) models to evaluate β-lactam synergy with daptomycin (DAP) against resistant enterococci. One E. faecalis strain (R6981) and two E. faecium strains (R6370 and 8019) were evaluated. DAP MICs were obtained. All strains were evaluated for response to LL37, an antimicrobial peptide, in the presence and absence of ceftaroline (CPT), ertapenem (ERT), and ampicillin (AMP). After 96 h, in vitro models were run simulating 10 mg DAP/kg body weight/day, 600 mg CPT every 8 h (q8h), 2 g AMP q4h, and 1 g ERT q24h, both alone and in combination against all strains. DAP MICs were 2, 4, and 4 μg/ml for strains R6981, R6370, and 8019, respectively. PK/PD models demonstrated bactericidal activity with DAP-CPT, DAP-AMP, and DAP-ERT combinations against strain 8019 (P < 0.001 and log10 CFU/ml reduction of >2 compared to any single agent). Against strains R6981 and R6370, the DAP-AMP combination demonstrated enhancement against R6370 but not R6981, while the combinations of DAP-CPT and DAP-ERT were bactericidal, demonstrated enhancement, and were statistically superior to all other regimens at 96 h (P < 0.001) against both strains. CPT, ERT, and AMP similarly augmented LL37 killing against strain 8019. In strains R6981 and R6370, CPT and ERT aided LL37 more than AMP (P < 0.001). Compared to DAP alone, combination regimens provide better killing and prevent resistance. Clinical research involving DAP combinations is warranted.

Unbound fraction of ertapenem in intensive care unit patients

OBJECTIVES

To determine unbound ertapenem concentrations in plasma and to describe the pharmacokinetics of unbound ertapenem in intensive care unit (ICU) patients.

PATIENTS AND METHODS

For assessing the influence of experimental conditions and for development of the ultrafiltration protocol, plasma from healthy volunteers was used. Concentrations of total and unbound ertapenem were determined by HPLC in 29 plasma samples from six ICU patients treated with 1 g of ertapenem once daily. The concentration-time courses were described by a one-compartment model. Ertapenem binding to albumin was assessed by Michaelis-Menten kinetics in solutions of human serum albumin, in plasma from healthy volunteers and in plasma from ICU patients.

RESULTS

The unbound fraction (fu) of ertapenem was highly susceptible to pH and temperature during ultrafiltration and was ∼20% in plasma from healthy volunteers at clinically relevant concentrations. In ICU patients, fu was substantially higher (range 30.9%-53.6%). The unbound concentrations of ertapenem exceeded 2 mg/L for 72% (median; range 39%-100%) of the 24 h dosing interval and 0.25 mg/L for 100% (range 79%-100%). The number of binding sites per albumin molecule was 1.22 (95% CI 1.07-1.38) in plasma from healthy volunteers and 0.404 (95% CI 0.158-0.650) in samples from ICU patients.

CONCLUSIONS

Determination of unbound ertapenem by ultrafiltration is susceptible to experimental conditions. When determined at physiological pH and temperature, fu of ertapenem is 2- to 4-fold higher than previously reported and even higher in ICU patients. Binding studies indicate that hypoalbuminaemia alone does not explain these differences. This issue should be further investigated for its clinical relevance.

Quantification and validation of ertapenem using a liquid chromatography-tandem mass spectrometry method

Ertapenem, a carbapenem, relies on time-dependent killing. Therapeutic drug monitoring (TDM) should be considered, when ertapenem is used in specific populations, to achieve optimal bactericidal activity and optimize drug-dosing regimens. No validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been reported using deuterated ertapenem as the internal standard. A new simple and robust LC-MS/MS method using a quadrupole mass spectrometer was developed for analysis of ertapenem in human plasma, using deuterated ertapenem as the internal standard. The calibration curve was linear over a range of 0.1 (lower limit of quantification [LLOQ]) to 125 mg/liter. The calculated accuracy ranged from -2.4% to 10.3%. Within-run coefficients of variation (CV) ranged from 2.7% to 11.8%, and between-run CV ranged from 0% to 8.4%. Freeze-thaw stability had a bias of -3.3% and 0.1%. Storage of QC samples for 96 h at 4°C had a bias of -4.3 to 5.6%, storage at room temperature for 24 h had a bias of -10.7% to -14.8%, and storage in the autosampler had a bias between -2.9% and -10.0%. A simple LC-MS/MS method to quantify ertapenem in human plasma using deuterated ertapenem as the internal standard has been validated. This method can be used in pharmacokinetic studies and in clinical studies by performing TDM.

Pharmacodynamic profiling of commonly prescribed antimicrobial drugs against Escherichia coli isolates from urinary tract

Since antimicrobial resistance among uropathogens against current first line agents has affected the management of severe urinary tract infection, we determined the likelihood that antibiotic regimens achieve bactericidal pharmacodynamic exposures using Monte Carlo simulation for five antimicrobials (ciprofloxacin, ceftriaxone, piperacillin/tazobactam, ertapenem, and meropenem) commonly prescribed as initial empirical treatment of inpatients with severe community acquired urinary tract infections. Minimum inhibitory concentration determination by Etest was performed for 205 Brazilian community urinary tract infection Escherichia coli strains from 2008 to 2012 and 74 E. coli bloodstream strains recovered from a surveillance study. Pharmacodynamic exposure was modeled via a 5000 subject Monte Carlo simulation. All isolates were susceptible to ertapenem and meropenem. Piperacillin/tazobactam, ceftriaxone and ciprofloxacin showed 100%, 97.5% and 83.3% susceptibility among outpatient isolates and 98.6%, 75.7% and 64.3% among inpatient isolates, respectively. Against outpatient isolates, all drugs except ciprofloxacin (82.7% in aggressive and 77.6% in conservative scenarios) achieved high cumulative fraction of response: carbapenems and piperacillin/tazobactam cumulative fraction of responses were close to 100%, and ceftriaxone cumulative fraction of response was 97.5%. Similar results were observed against inpatients isolates for carbapenems (100%) and piperacillin/tazobactam (98.4%), whereas ceftriaxone achieved only 76.9% bactericidal cumulative fraction of response and ciprofloxacin 61.9% (aggressive scenario) and 56.7% (conservative scenario) respectively. Based on this model, standard doses of beta-lactams were predicted to deliver sufficient pharmacodynamic exposure for outpatients. However, ceftriaxone should be avoided for inpatients and ciprofloxacin empirical prescription should be avoided in both inpatients and outpatients with complicated urinary tract infection.