Simultaneous Determination of Ceftazidime in Three Different Pharmaceutical Preparations Combined with Either Tazobactam, Tobramycin or Sulbactam by HPTLC-Spectrodensitometric Method

A new, simple hight performance thin layer chromatography (HPTLC)-Spectrodensitometric strategy was created and approved for the synchronous estimation of four antibacterial specialists: ceftazidime (CEF), tazobactam (TAZ), tobramycin (TOB) and sulbactam (SUL). The four compounds were separated on TLC aluminum plates covered with silica gel 60 F254, using chloroform-acetonitrile-methanol-ammonia (4:1:0.5:0.15, v/v/v/v) as a mobile phase at 254 nm. Linear correlation was obeyed over the concentration ranges of 12.0-72.0, 2.0-12.0, 3.0-18.0 and 10.0-50.0 μg mL-1 for CEF, TAZ, TOB and SUL, respectively. The proposed approach is efficient, repeatable and convenient as a flexible method for the quality control of diverse combinations of these pharmaceuticals in various pharmaceutical preparations, with high percent recoveries that are highly consistent with labeled data. When the findings of the proposed technique were compared to those of the comparison methods, there were no critical contrasts in terms of precision and accuracy.

In vitro and in vivo evaluation of two combined β-lactamase inhibitors against carbapenem-resistant Acinetobacter baumannii

The objective of this study was to evaluate the in vitro and in vivo efficacy of clavulanic acid (C/A) in combination with tazobactam against clinical strains of carbapenem-resistant Acinetobacter baumannii. The MIC of 24 clinical strains of A. baumannii was determined, and a checkerboard assay and time-kill curve analysis were performed in selected strains to determine the synergy between C/A and tazobactam. The efficacy of C/A in monotherapy and in combination with tazobactam was evaluated in vitro in cell culture experiments and in a murine peritoneal sepsis model. The C/A and C/A plus tazobactam MIC50 were 128 and <1 mg/L, respectively. The checkerboard assay showed that tazobactam (4 and 8 mg/L) demonstrated synergy with C/A against A. baumannii Ab40, an OXA-24 producer strain, and Ab293, a lacking OXA β-lactamase strain. The time-kill curve assay showed both bactericidal and synergistic effects against Ab40 and Ab293, with C/A 1xMIC and tazobactam (4 and 8 mg/L) at 24 h. In the murine peritoneal sepsis model with Ab293 strain, the combination of C/A and tazobactam reduced bacterial loads in tissues and blood by 2 and 4 log10 CFU/g or mL compared with C/A alone. Combining C/A with tazobactam could be considered as a potential alternative strategy to treat A. baumannii in some cases, and future work with more strains is needed to confirm this possibility.

Ceftolozane-Tazobactam Pharmacokinetics in the Abdominal Tissue of Patients Undergoing Lower Gastrointestinal Surgery: Dosing Considerations Based on Site-Specific Pharmacodynamic Target Attainment

INTRODUCTION

Recently, complicated intra-abdominal infections (cIAI) have been caused not only by Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, and Pseudomonas aeruginosa, but also by extended-spectrum β-lactamase-producing Enterobacterales members. Ceftolozane-tazobactam (CTLZ-TAZ) is considered to exhibit therapeutic effects against cIAI. Studies on the concentrations of antibiotics in abdominal tissues directly affected by cIAI are limited. Therefore, in this study, we investigated the pharmacokinetics of CTLZ-TAZ in abdominal tissue and simulated the administration regimen required to achieve the pharmacodynamic target for cIAI-causing bacteria.

METHODS

Patients scheduled for elective lower gastrointestinal surgery were intravenously administered preoperative CTLZ-TAZ (1 g CTLZ and 0.5 g TAZ). Plasma, peritoneal fluid, peritoneum, and subcutaneous adipose tissue samples were collected during the surgery, and CTLZ as well as TAZ concentrations were measured. The noncompartmental and compartmental pharmacokinetic parameters were then estimated. Site-specific pharmacodynamic target attainment analysis using 1.5 g of CTLZ-TAZ was performed.

RESULTS

CTLZ-TAZ was administered to nine patients (once to five patients and twice to four patients). The mean peritoneal fluid-to-plasma ratio (one dose/two doses) for CTLZ was 0.74/1.15, which was slightly higher than the mean peritoneal fluid-to-plasma ratio for TAZ (0.95/1.13). The ratio for subcutaneous adipose was lower than those for peritoneal fluid and peritoneum tissues. We also discovered that the average ratio of CTLZ and TAZ concentrations in all tissues was maintained at or above 2:1. In our investigation of pharmacodynamic target attainment in each tissue, the desired bactericidal effect was attained with all CTLZ-TAZ (1.5 g) administration regimens [q12h (3 g/day), q8h (4.5 g/day), and q6h (6 g/day)].

CONCLUSION

To the best of our knowledge, this is the first study investigating the optimal pharmacodynamic level of CTLZ-TAZ in the abdominal tissue against cIAI-causing bacteria. This study also serves as a guideline for designing an optimal administration regimen based on pharmacodynamic target attainment for cIAI-causing bacteria.

DETAILS OF THE TRIAL REGISTRATION

The institutional review board of Hiroshima University Hospital, CRB6180006. The Japan Registry of Clinical Trials, jRCTs061190025.

In vitro study of elution kinetics and biological activity of piperacillin/tazobactam and gentamicin in acrylic bone cement

BACKGROUND

Antibiotics differ in their elution characteristics from bone cement. But no such data is available on piperacillin and tazobactam. Therefore, we performed an in vitro observational study to examine (1) in vitro elution characteristics of piperacillin and tazobactam from bone cement, (2) their biological activity using minimum inhibitory concentration and (3) elution characteristics and biological activity when combined with gentamicin in bone cement.

HYPOTHESIS

The null hypothesis was that piperacillin and tazobactam after elution from bone cement can achieve concentrations higher than minimum inhibitory concentration.

MATERIAL AND METHODS

Forty milligrams bone cement was mixed with the following combination of antibiotics: without any antibiotic (sample A, control), 4g/0.50g piperacillin/tazobactam (sample B), 6g/0.75g piperacillin/tazobactam (sample C), 8g/1.0g piperacillin/tazobactam (sample D) and 4g/0.50g piperacillin/tazobactam and 400mg gentamicin (sample E). Samples were analysed on reverse-phase ultra-high-performance liquid chromatography. Antibacterial activity in the elute were tested against standard American Type Culture Collection (ATCC) strains.

RESULTS

Detectable drug elution for piperacillin and tazobactam was seen till 21days. Peak drug levels for all formulations were seen at 48hours (140.8 & 297.5μg/mL for samples B of piperacillin and tazobactam respectively). About 0.83-1.24% of piperacillin and 23.17-29.17% of tazobactam were released from the samples. Gentamicin improved elution of piperacillin and tazobactam: 140.8 vs. 919.9μg/mL (p=0.000) for samples B & E of piperacillin respectively and 297.5 & 1138.4μg/mL (p=0.001) for samples B & E of tazobactam respectively at 2days. Sample E showed complete inhibition of tested microorganisms, while B sample was microbiologically less active compared to E on day 5.

CONCLUSIONS

Piperacillin and tazobactam eluted successfully from bone cement and also retained antimicrobial activity after elution. Maximum elution was seen up to day 2 after which it reduced drastically. Antimicrobial action was seen up to 7days.

LEVEL OF EVIDENCE

III; comparative study.

Population pharmacokinetics of piperacillin in critically ill children including those undergoing continuous kidney replacement therapy

OBJECTIVES

Despite that piperacillin-tazobactam combination is commonly used in critically ill children, increasing evidence suggests that the current dosing schedules are not optimal for these patients. The aim of this work is to develop a population pharmacokinetic (PK) model for piperacillin to evaluate the efficacy of standard dosing in children with and without kidney replacement therapy (CKRT), and to propose alternative dosing schemes maximizing target attainment.

METHODS

429 piperacillin concentrations measured in different matrices, obtained from 32 critically ill children (19 without CKRT, 13 with CKRT) receiving 100 mg/kg of piperacillin/tazobactam every 8 hours (increased to 12h after the 4th dose) were modelled simultaneously using the population approach with NONMEM 7.4. The percentage of patients with 90% fT>MIC and target attainment (percentage of dosing interval above MIC) were estimated for different intermittent and continuous infusions in the studied population.

RESULTS

Piperacillin PK was best described with a two-compartment model. Renal (CL_R), nonrenal (CL_M), and hemofilter (CL_CKRT) clearances were found to be influenced by the glomerular filtration rate, height (CL_R), weight (CL_M) and filter surface (CL_CKRT). Only 7 (37%) children without CKRT and 7 (54%) with CKRT achieved 90% fT >MIC with the current dosing schedule. Of the alternative regimens evaluated, a 24h continuous infusion of 200 mg/kg (CKRT) and 300 mg/kg (no CKRT) provided 100% fT >MIC(≤16mg/L) and target attainments ≥90% across all evaluated MICs.

CONCLUSIONS

In children with and without CKRT, standard dosing failed to provide an adequate systemic exposure, while prolonged and continuous infusions showed an improved efficacy.

Estimation of cefepime, piperacillin, and tazobactam clearance with iohexol-based glomerular filtration rate in paediatric patients

PURPOSE

Estimated glomerular filtration rate (eGFR) equations reflect kidney function imprecisely. We aimed to describe whether iohexol-based GFR or eGFRs predict clearance of cefepime, piperacillin, and tazobactam in pharmacokinetic (PK) models in this population and its clinical significance.

METHODS

Hospitalized patients (0.5-25 years) with haemato-oncological disease and infection receiving cefepime or piperacillin/tazobactam were included. PK samples were collected at a steady state concomitantly with samples for iohexol-based GFR. PK models were developed in NONMEM. Weight, postmenstrual age, iohexol-based GFR, different eGFR equations (Schwartz updated, Lund-Malmö revised, CKD-EPI, Bouvet, Schwartz cystatin C-based) were tested as covariates. Probabilities of neurotoxic/therapeutic concentrations were assessed by simulations.

RESULTS

Fifteen patients receiving cefepime and 17 piperacillin/tazobactam were included (median (range) age 16.2 (1.9-26.0) and 10.5 (0.8-25.6) years, iohexol-based GFR 102 (68-140) and 116 (74-137) mL/min/1.73 m², respectively). Two-compartment model provided the best fit for all drugs. Weight was covariate for central and peripheral compartment, clearance and intercompartmental clearance (only tazobactam), and postmenstrual age for clearance (excluding cefepime). Iohexol-based GFR was the best predictor of clearance. The model of cefepime without vs with iohexol-based GFR underestimated the probability of neurotoxic concentrations (28.3-28.6% vs 52.1-69.3%) and overestimated the probability of therapeutic concentrations (> 90% vs 81.9-87.1%) in the case of iohexol-based GFR 70-80 and 130-140 mL/min/1.73 m², respectively.

CONCLUSION

Iohexol-based GFR can predict better than eGFRs the clearance of cefepime, piperacillin, and tazobactam in children and young adults with haemato-oncological disease and infection, warranting further investigation as an indicator of renal function to improve targeting of therapeutic window.

TRIAL REGISTRATION NUMBER AND DATE OF REGISTRATION

EudraCT 2015-000,631-32, EudraCT 2016-003,374-40 (24.10.2016).

Ceftolozane/tazobactam for refractory P. aeruginosa endocarditis: A case report and pharmacokinetic analysis

We describe a case of a 48 years old male with left sided endocarditis and septic emboli secondary to a Pseudomonas aeruginosa strain that developed resistance to other β-lactam antibiotics during therapy resulting in prolonged bacteremia. Blood cultures sterilized within 1 day of initiating ceftolozane/tazobactam 3 g every 8 hours in combination with ciprofloxacin. Steady state free ceftolozane plasma Cmax and Cmin concentrations were calculated to be 122.2μg/mL and 24.3μg/mL, respectively. The multidrug-resistant strain harbored chromosomal β-lactamases OXA-486 and PDC-3, mutations in ampD and dacB predicted to lead to ampC over-expression, and mutations in OprD predicted to decrease outer membrane permeability. Following completion of a 42 day course and aortic valve replacement, the patient was deemed clinically cured without recurrence of infection at follow up 2 years later. To our knowledge, this is the first reported case to measure ceftolozane concentrations during the treatment of endocarditis which supports dose optimization approaches of severe endovascular disease due to multidrug resistant pathogens.

Systematic Literature Review of Real-world Evidence of Ceftolozane/Tazobactam for the Treatment of Respiratory Infections

Introduction

Gram-negative nosocomial pneumonia (NP), including hospital-acquired bacterial pneumonia (HABP), ventilated HABP (vHABP), and ventilator-associated bacterial pneumonia (VABP), is a significant cause of morbidity and mortality. Common pathogens, including Enterobacterales and Pseudomonas aeruginosa, are prevalent in healthcare settings and have few effective treatment options due to high rates of antibacterial resistance. Resistant pathogens are associated with significantly worse outcomes, relative to patients with susceptible infections. Ceftolozane/tazobactam (C/T) has established efficacy in clinical trials of patients with NP. This review aims to collate data on C/T use for HABP/vHABP/VABP infections in real-world clinical practice.

Methods

This systematic literature review searched online biomedical databases for real-world studies of C/T used to treat Gram-negative respiratory tract infections (RTIs) between January 2009 and June 2020.

Results

Thirty-three studies comprising 658 patients were identified. Pneumonia was the most common infection treated with C/T (85%), with a smaller number of unspecified RTIs (9%) and tracheobronchitis (5%) reported. The majority of patients had respiratory infections caused by P. aeruginosa (92.8%), of which 88.1% were multidrug-resistant. Examination of these studies demonstrated an increase in the percentage of patients receiving the recommended dose of C/T for respiratory infections (3 g q8h or renal impairment-adjusted) over time (36.8% of patients in 2017 to 71.5% in 2020). Clinical success rates ranged from 51.4 to 100%, with 10 studies (55.6% of studies reporting clinical success) reporting clinical success rates of > 70%; microbiological success rates ranged from 57.0 to 100.0%, with three studies (60.0% of studies reporting microbiological success) reporting microbiological success rates of > 70%. Thirty-day mortality ranged from 0.0 to 33.0%, with nine studies (90% of studies reporting mortality) reporting 30-day mortality of < 30%.

Conclusions

The studies identified in this review demonstrate that C/T shows similar outcomes as those seen in clinical trials, despite the higher frequency of multidrug-resistant pathogens, and comorbidities that may have been excluded from the trials.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40121-021-00491-x.

Third-generation cephalosporin resistance in clinical isolates of Enterobacterales collected between 2016-2018 from USA and Europe: genotypic analysis of β-lactamases and comparative in vitro activity of cefepime/enmetazobactam

OBJECTIVES

This study aimed to investigate third-generation cephalosporin (3GC) resistance determinants [extended-spectrum β-lactamases (ESBLs), AmpC β-lactamases and OXA-type β-lactamases] in contemporary clinical Enterobacterales isolates and to determine the in vitro activity of β-lactams and β-lactam/β-lactamase inhibitor combinations, including the investigational combination of cefepime and the novel β-lactamase inhibitor enmetazobactam.

METHODS

Antibacterial susceptibility of 7168 clinical Enterobacterales isolates obtained between 2016-2018 from North America and Europe was determined according to CLSI guidelines. Phenotypic resistance to the 3GC ceftazidime (MIC ≥ 16 µg/mL) and/or ceftriaxone (MIC ≥ 4 µg/mL) but retaining susceptibility to meropenem (MIC ≤ 1 µg/mL) was determined. β-Lactamase genotyping was performed on clinical isolates with ceftazidime, ceftriaxone, cefepime or meropenem MIC ≥ 1 µg/mL.

RESULTS

Phenotypic resistance to 3GCs occurred in 17.5% of tested isolates, whereas 2.1% of isolates were resistant to the carbapenem meropenem. Within the 3GC-resistant subgroup, 60.1% (n = 752) of isolates encoded an ESBL, 25.6% (n = 321) encoded an AmpC-type β-lactamase and 0.9% (n = 11) encoded an OXA-type β-lactamase. Susceptibility of the subgroup to piperacillin/tazobactam (57.5%) and ceftolozane/tazobactam (71.3%) was <90% based on breakpoints established by the CLSI. Projected susceptibility to cefepime/enmetazobactam was 99.6% when applying the cefepime susceptible, dose-dependent breakpoint of 8 µg/mL. Against ESBL-producing isolates (n = 801) confirmed by genotyping, only susceptibility to meropenem (96.0%) and cefepime/enmetazobactam (99.9%) exceeded 90%.

CONCLUSION

This study describes the antibacterial activity of important therapies against contemporary 3GC-resistant clinical Enterobacterales isolates and supports the development of cefepime/enmetazobactam as a carbapenem-sparing option for ESBL-producing pathogens.

Piperacillin-Tazobactam Hypersensitivity: A Large, Multicenter Analysis

BACKGROUND

Piperacillin/tazobactam is a broad-spectrum penicillin. Hypersensitivity reactions are less commonly reported than with other penicillins except in patients with cystic fibrosis.

OBJECTIVE

Detailed clinical characterization of a patient cohort referred with suspected piperacillin-tazobactam hypersensitivity.

METHODS

Retrospective analysis of the demographic characteristics, clinical presentation, investigation, and management of 87 patients presenting to 5 European allergy centers. Patients underwent skin prick and intradermal testing with piperacillin/tazobactam, major (penicilloyl-polylysine) and minor (sodium penilloate) determinants, amoxicillin, benzylpenicillin, flucloxacillin, co-amoxiclav, clavulanic acid, and meropenem with immediate and, where appropriate, delayed reading of tests. Skin test-negative patients underwent drug provocation to piperacillin/tazobactam and/or other penicillins. A multistep protocol was used, depending on risk assessment.

RESULTS

Forty-eight of 87 (55%) patients were diagnosed with hypersensitivity to piperacillin/tazobactam with either positive skin or drug provocation test results, of whom 10 (21%) had a diagnosis of cystic fibrosis. Twenty-six (54%) patients presented with immediate and 22 (45%) with nonimmediate hypersensitivity. Patients with cystic fibrosis predominantly presented with nonimmediate hypersensitivity (70%). Reactions were severe in 52% of immediate reactors (Brown's anaphylaxis grade 3) and moderately severe (systemic involvement) in 75% of nonimmediate reactors. The number of patients with negative skin test results tolerating reintroduction was comparable in immediate (80%) and nonimmediate (88%) hypersensitivity. One-third of patients were cross-sensitized to other penicillins. The cross-sensitization pattern raised the possibility of tazobactam allergy in 3 patients. In 21 patients selectively sensitized to piperacillin/tazobactam (12 immediate, 9 nonimmediate), tolerance to other beta-lactams was demonstrated by drug provocation testing.

CONCLUSIONS

Piperacillin-tazobactam caused immediate and nonimmediate hypersensitivity with similar frequency. Most patients were selectively sensitized and tolerated other penicillins. Some patients may be allergic to the beta-lactamase inhibitor only.

Development and validation of a quantitative LC-MS/MS method for the simultaneous determination of ceftolozane and tazobactam in human plasma and urine

The purpose of this work was to develop and validate a single sensitive, selective and rapid bioanalytical method to determine ceftolozane and tazobactam concentrations in human plasma and urine and to use this method to analyze samples from a human clinical study. Human plasma and urine samples were prepared by protein precipitation using a solution of acetonitrile, water and formic acid. Following protein precipitation, samples were analyzed by liquid chromatography tandem mass spectrometry. Chromatographic resolution was achieved on a Kinetex PFP column using a gradient elution, a flow rate of 0.4 mL/min, and a total run time of 5 min. Positive electrospray ionization was employed and analytes were quantitated using multi-reaction monitoring mode. Method validation was conducted in accordance with Unites States Food and Drug Administration's regulatory guidelines for bioanalytical method validation. Calibration curves were determined to linear over the range of 0.1 to 40 µg/mL for ceftolozane and 0.05 to 20 µg/mL for tazobactam. The method was determined to be accurate (-6.24 to 12.53 percent relative error), precise (less than 13.28 percent standard deviation) and sensitive in both human plasma and urine. Ceftolozane and tazobactam were determined to be stable across a battery of stability studies including autosampler, benchtop, freeze/thaw and long-term stability. This validated method successfully applied to human clinical samples to determine the concentration versus time profiles of the intravenously administered combination of Zerbaxa (ceftolozane-tazobactam) in burn patients.

Epidermoid cyst abscess of the neck masquerading as a thyroid abscess

SUMMARY

In this case report, we describe a 37-year-old male who presented with fever and tender neck mass. Neck ultrasonography revealed a mixed echogenic multiloculated solid-cystic lesion containing turbid fluid and occupying the right thyroid region. Thyroid function tests showed subclinical hyperthyroidism. The patient was initially diagnosed with thyroid abscess and he was subsequently treated with percutaneous aspiration and i.v. antibiotics; however, his clinical symptoms did not improve. Surgical treatment was then performed and a pathological examination revealed a ruptured epidermoid cyst with abscess formation. No thyroid tissue was identified in the specimen. The patient was discharged uneventfully. However, at the 3-month and 1-year follow-ups, the patient was discovered to have developed subclinical hypothyroidism. Neck ultrasonography revealed a normal thyroid gland. This report demonstrates a rare case of epidermoid cyst abscess in the cervical region, of which initial imaging and abnormal thyroid function tests led to the erroneous diagnosis of thyroid abscess.

LEARNING POINTS

Epidermoid cyst abscess at the cervical region can mimic thyroid abscess. Neck ultrasonography cannot distinguish thyroid abscess from epidermoid cyst abscess. Thyroid function may be altered due to the adjacent soft tissue inflammation.

Influence of extracorporeal membrane oxygenation on the pharmacokinetics of ceftolozane/tazobactam: an ex vivo and in vivo study

Background

Extracorporeal membrane oxygenation (ECMO) is increasingly used in intensive care units and can modify drug pharmacokinetics and lead to under-exposure associated with treatment failure. Ceftolozane/tazobactam is an antibiotic combination used for complicated infections in critically ill patients. Launched in 2015, sparse data are available on the influence of ECMO on the pharmacokinetics of ceftolozane/tazobactam. The aim of the present study was to determine the influence of ECMO on the pharmacokinetics of ceftolozane-tazobactam.

Methods

An ex vivo model (closed-loop ECMO circuits primed with human whole blood) was used to study adsorption during 8-h inter-dose intervals over a 24-h period (for all three ceftolozane/tazobactam injections) with eight samples per inter-dose interval. Two different dosages of ceftolozane/tazobactam injection were studied and a control (whole blood spiked with ceftolozane/tazobactam in a glass tube) was performed. An in vivo porcine model was developed with a 1-h infusion of ceftolozane–tazobactam and concentration monitoring for 11 h. Pigs undergoing ECMO were compared with a control group. Pharmacokinetic analysis of in vivo data (non-compartmental analysis and non-linear mixed effects modelling) was performed to determine the influence of ECMO.

Results

With the ex vivo model, variations in concentration ranged from − 5.73 to 1.26% and from − 12.95 to − 2.89% respectively for ceftolozane (concentrations ranging from 20 to 180 mg/l) and tazobactam (concentrations ranging from 10 to 75 mg/l) after 8 h. In vivo pharmacokinetic exploration showed that ECMO induces a significant decrease of 37% for tazobactam clearance without significant modification in the pharmacokinetics of ceftolozane, probably due to a small cohort size.

Conclusions

Considering that the influence of ECMO on the pharmacokinetics of ceftolozane/tazobactam is not clinically significant, normal ceftolozane and tazobactam dosing in critically ill patients should be effective for patients undergoing ECMO.

Validation and clinical application of a multiplex high performance liquid chromatography - tandem mass spectrometry assay for the monitoring of plasma concentrations of 12 antibiotics in patients with severe bacterial infections

OBJECTIVE

Unpredictable pharmacokinetics of antibiotics in patients with life-threatening bacterial infections is associated with drug under- or overdosing. Therapeutic drug monitoring (TDM) may guide dosing adjustment aimed at maximizing antibacterial efficacy and minimizing toxicity. Rapid and accurate analytical methods are key for real-time TDM. Our objective was to develop a robust high-performance liquid chromatography-tandem mass spectrometry method (HPLC-MS/MS) for multiplex quantification of plasma concentrations of 12 antibiotics: imipenem/cilastatin, meropenem, ertapenem, cefepime, ceftazidime, ceftriaxone, piperacillin/tazobactam, amoxicillin, flucloxacillin, rifampicin, daptomycin.

METHODS

A single extraction procedure consisting in methanol plasma protein precipitation and H₂O dilution was used for all analytes. After chromatographic separation on an Acquity UPLC HSS-T3 2.1 × 50 mm, 1.8 µm (Waters®) column, quantification was performed by electro-spray ionisation-triple quadrupole mass spectrometry with selected reaction monitoring detection. Antibiotics were divided in two pools of calibration according to the frequency of analyses requests in the hospital routine antibiotic TDM program. Stable isotopically-labelled analogues were used as internal standards. A single analytical run lasted less than 9 min.

RESULTS

The method was validated based on FDA recommendations, including assessment of extraction yield (96-113.8%), matrix effects, and analytical recovery (86.3-99.6%). The method was sensitive (lower limits of quantification 0.02-0.5 µg/mL), accurate (intra/inter-assay bias -11.3 to +12.7%) and precise (intra/inter-assay CVs 2.1-11.5%) over the clinically relevant plasma concentration ranges (upper limits of quantification 20-160 µg/mL). The application of the TDM assay was illustrated with clinical cases that highlight the impact on patients' management of an analytical assay providing information with short turn-around time on antibiotic plasma concentration.

CONCLUSION

This simple, robust high-throughput multiplex HPLC-MS/MS assay for simultaneous quantification of plasma concentrations of 12 daily used antibiotics is optimally suited for clinically efficient real-time TDM.

Piperacillin enhances the inhibitory effect of tazobactam on β-lactamase through inhibition of organic anion transporter 1/3 in rats

To assess the mechanism of the pharmacokinetic interaction between piperacillin and tazobactam, renal excretion and pharmacokinetic studies of piperacillin/tazobactam were investigated in normal and bacteremia rats. A bacteremia model was established to investigate the pharmacokinetic properties of piperacillin and tazobactam under different conditions. Renal slices were taken to examine the uptake of piperacillin and tazobactam. Pharmacokinetic studies of β-lactamase in rats were performed to study the contribution of rOat1/3 to the inhibition of tazobactam on β-lactamase. The AUC (from 2.93 ± 0.58 to 6.52 ± 1.44 mg·min/ml) and the plasma clearance (CL_P ) (from 2.41 ± 1.20 to 0.961 ± 0.212 ml/min/kg) of tazobactam were both altered after the intravenous coadministration of piperacillin and tazobactam in the bacteremia rats. The renal clearance (CL_R ) of tazobactam decreased from 1.30 ± 0.50 to 0.361 ± 0.043 ml/min/kg. In summary, there was a beneficial interaction between piperacillin and tazobactam mediated by rOat1 and rOat3. Piperacillin enhances the inhibitory effect of tazobactam on β-lactamase through the inhibition of rOat1 and rOat3 in rats. The contribution rate of rOat1/3 for the synergistic effect was 20% when the two drugs were coadministered.

[Piperacillin/tazobactam plus amikacin vs. piperacilin/tazobactam: treatment for children with febrile neutropenia]

BACKGROUND

Pediatric patients with febrile neutropenia usually receive a combination of broad spectrum antimicrobials. Treatment without aminoglycoside seems to have advantages.

OBJECTIVE

To compare the efficacy of piperacillin/tazobactam plus amikacin versus piperacillin/tazobactam.

METHODS

Randomized, open label, controlled clinical trial. Sample size for an efficacy of 55%, and delta of 25%; 80 episodes were required for each group. Selection criteria were patients with febrile neutropenia, candidates to receive parenteral antimicrobial treatment; they were randomized to one of two groups, piperacillin/tazobactam plus amikacin (Group A), or piperacillin/tazobactam (Group B). The outcomes were failure, adverse events and death. Mantel-Haenszel chi squaretest and exact Fisher test were used. Reduction of relative and absolute risk (RRR and ARR), 95% confidence intervals (CI 95%) and number needed to treat (NNT) were calculated.

RESULTS

88 Episodes were analyzed in group A and 76 in group B. There was no statistical difference in general characteristics of patients or type of infections. There was not significant statistical difference in: failure 31.8% group A, 30.2% group B (RR 1.05, CI 95% 0.66-1.66, p = 0.86), or adverse events (one in each group). The RRR was 1.5%, and ARR 2%, with a NNT of 67.

CONCLUSION

Piperacillin/tazobactam without amikacin was as effective as combination therapy in pediatric patients with febrile neutropenia.

Urinary piperacillin/tazobactam pharmacokinetics in vitro to determine the pharmacodynamic breakpoint for resistant Enterobacteriaceae

Urinary tract infections caused by multidrug-resistant Enterobacteriaceae are a growing burden worldwide. Recent studies of urinary pharmacokinetics described high piperacillin/tazobactam (TZP) concentrations in urine, but it is unknown whether this results in treatment efficacy. This study investigated the pharmacodynamics of TZP in a static in vitro model for Enterobacteriaceae to determine the concentration-effect relationship and ultimately the required free (unbound) time above the minimum inhibitory concentration (fT_>MIC) required for bacterial killing. The static simulation model investigated TZP fT_>MIC between 0% and 100%. Resistant Escherichia coli and Klebsiella pneumoniae isolates with piperacillin/tazobactam MICs of 4096/512, 1024/128 and 128/16 mg/L were investigated; two of the three organisms were carbapenemase-producers. Clinical efficacy was determined as a 3-log reduction over the dosing interval by comparing interval growth with controls. TZP was observed to exhibit time dependence for all organisms. The fT_>MIC was determined to be 37.5%, 37.5% and 50% for MICs of 4096/512, 1024/128 and 128/16 mg/L, respectively. Linear regression identified the overall target to be 49.85 ± 16.9% fT_>MIC. In conclusion, bactericidal activity against TZP-resistant Enterobacteriaceae occurred at 49.85 ± 16.9% fT_>MIC. This suggests that highly resistant urinary organisms, including carbapenemase-producers, with MICs up to 4096/512 mg/L could be treated with TZP. Further investigations are required to elucidate urinary breakpoints and to explore the impact of different resistance mechanisms.

Measurement of ceftolozane and tazobactam concentrations in plasma by UHPLC-MS/MS. Clinical application in the management of difficult-to-treat osteoarticular infections

BACKGROUND

Ceftolozane, in combination with the β-lactamase inhibitor tazobactam, is a new option in the pipeline against multidrug-resistant Gram-negative bacilli. As for other β-lactam antibiotics, optimizing the use of ceftolozane-tazobactam is advisable, especially in difficult-to-treat infections. In this regard, therapeutic drug monitoring would be required to guide the treatment of ceftolozane-tazobactam. Thus, we aimed to develop and validate procedures based on UHPLC-MS/MS for measurement of ceftolozane and tazobactam plasma concentrations in clinical practice.

MATERIAL AND METHODS

Analyses were conducted using an Acquity® UPLC® integrated system coupled to an Acquity® TQD® tandem-quadrupole mass spectrometer. Ceftolozane, tazobactam and their internal standards (ceftazidime-D₅ and sulbactam) were detected by electrospray ionization mass spectrometry in positive and negative ion multiple reaction monitoring modes, using transitions of 667.2 → 199.3/139.0 and 551.9 → 467.9 for ceftolozane and ceftazidime-D₅, and 299.0 → 138/254.9 and 232.0 → 140.0 for tazobactam and sulbactam. Measurement procedures developed were used for guiding the treatment and adjusting daily dose of ceftolozane-tazobactam in patients with osteoarticular infections.

RESULTS

Coefficients of variation and absolute relative biases were <7.9% and 6.5% in all cases. The lower limit of quantification, linearity, normalized-recoveries, normalized-matrix effects and measurement uncertainties for ceftolozane were: 0.97 mg/L, (0.97-125) mg/L, ≤113.6%, ≤108.7%, and ≤ 18.7%, respectively; and for tazobactam: 1.04 mg/L, (1.04-125) mg/L, ≤103.6%, ≤101.9%, and ≤ 20.0%. No interferences and carry-over were observed. Patients plasma concentrations were higher than the recommended 3-4 times the minimal inhibitory concentrations.

CONCLUSIONS

Our measurement procedures are suitable for therapeutic drug monitoring of ceftolozane-tazobactam in patients with osteoarticular infections.

Therapeutic drug monitoring of piperacillin and tazobactam by RP-HPLC of residual blood specimens

BACKGROUND

Sepsis is a common diagnosis in critical care with inpatient mortality rates up to 50%. Sepsis care is organized around source control, antibiotics, and supportive care. Drug disposition is deranged by changes in volume of distribution and regional blood flow, as well as multiple organ failure. Thus, assuring that each patient with sepsis attains pharmacokinetic targets is challenging. There is currently no commercially available FDA-approved assay to measure piperacillin-tazobactam, very commonly used as a beta-lactam/beta-lactamase inhibitor combination antibiotic in the intensive care unit (ICU).

METHODS

Samples were prepared by ultrafiltration of plasma collected in lithium heparin Vacutainers. Separation was achieved by gradient elution on a C-18 column followed by UV detection at 214 nm. The method is validated in residual blood samples allowing investigators to exploit a waste product to develop insight into beta-lactam pharmacokinetics in the ICU.

RESULTS

Accuracy and precision were within the 25% CLIA error standard for other antibiotic assays. Free piperacillin concentrations were also in good agreement with total piperacillin concentrations measured in the same plasma by an assay in clinical use outside the United States.

CONCLUSION

We describe a method for measuring piperacillin and tazobactam that meets clinical validation standards. Quick turnaround time and excellent accuracy on a low-cost platform make this method more than adequate for use as a routine therapeutic drug monitoring tool.

Humanized Exposures of a β-Lactam-β-Lactamase Inhibitor, Tazobactam, versus Non-β-Lactam-β-Lactamase Inhibitor, Avibactam, with or without Colistin, against Acinetobacter baumannii in Murine Thigh and Lung Infection Models

β-lactam-β-lactamase inhibitors (BLIs) have previously demonstrated antimicrobial activity against Acinetobacter baumannii (AB). Colistin retains the highest susceptibility rate against A. baumannii, and has demonstrated synergy with other antimicrobials, including β-lactam-BLIs. Therefore, we assessed the potential individual activity and synergistic combinations in vivo against carbapenem-susceptible (CS) and multidrug-resistant (MDR) A. baumannii isolates in neutropenic thigh and lung infection models. In vitro, colistin and tazobactam MICs were 1 and 16 µg/mL against AB 25-49 (CS) and 1 and 128 µg/mL against AB 5075 (MDR) respectively. In the lung model, tazobactam alone and in combination with colistin achieved a 1-log reduction in CFU, while colistin alone was not active against AB 25-49. No activity was observed against AB 5075. In the thigh model, tazobactam with and without colistin was bacteriostatic against AB 25-49 but did not demonstrate any activity against AB 5075. Avibactam and colistin alone and in combination were not active against either isolate. No synergy was observed; however, we found tazobactam activity against A. baumannii. This activity was not observed for the non-β-lactam-BLI, avibactam. This suggests that binding to penicillin-binding proteins of the β-lactam molecule is required for tazobactam activity against A. baumannii. These data point to an added role of β-lactam-BLIs beyond their primary purpose of β-lactamase inhibition in the treatment of MDR A. baumannii infections by enhancing the activity of peptide antibiotics, a property that is not shared by the novel non-β-lactam-BLIs. Future studies are needed to define tazobactam and colistin activity in an A. baumannii infection model.

Improvement of Bolton broth by supplementation with tazobactam for the isolation of Campylobacter from chicken rinses

Overgrowth of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli (E. coli) on Campylobacter media prevents the latter's selective isolation, thereby making the improvement of Campylobacter-selective media necessary. We evaluated tazobactam (an ESBL inhibitor) to supplement Bolton enrichment broth (Tz-Bolton broth) for the selective isolation of Campylobacter in chicken carcass rinses. First, using 20 strains of ESBL-producing E. coli and 13 Campylobacter strains, we found 4 μg/mL of tazobactam to be optimal for inhibiting the ESBL-producing E. coli while allowing the growth of all tested Campylobacter strains. Next, 80 whole chicken carcasses were rinsed with buffered peptone water (BPW), and 25 mL of BPW rinse was mixed with 2 × blood-free Bolton broth (25 mL) with or without tazobactam followed by incubation at 42°C for 48 h under microaerobic conditions. A loopful of the incubated broth was inoculated on modified charcoal-cefoperazone-deoxycholate agar (mCCDA) and microaerobically incubated at 42°C for 48 h. The tazobactam supplemented Bolton broth showed a higher Campylobacter isolation rate (38.8%, p < 0.05) than normal Bolton broth (15%). Moreover, the number of mCCDA plates with non-Campylobacter was much lower (p < 0.05) after enrichment in Tz-Bolton broth (0%) than in the normal Bolton broth (80%), suggesting that selectivity of the modified broth was superior to normal Bolton broth.

Use of ceftolozane-tazobactam in a cystic fibrosis patient with multidrug-resistant pseudomonas infection and renal insufficiency

We report the successful use of ceftolozane/tazobactam (C/T) to treat a pulmonary exacerbation in a 35 year old female, post lung transplant, with cystic fibrosis (CF), malnutrition, chronic kidney disease, and multi-drug resistant Pseudomonas aeruginosa infection (MDR PSA). Given the complexity of the clinical profile, we measured drug levels of C/T during treatment of her current exacerbation to determine pharmacokinetics. The patient achieved an estimated ceftolozane peak of 174.1 μg/mL and trough of 9.2 μg/mL. Serum half-life was found to be slightly shorter than previously reported in normal subjects, (2.3 hr. vs. 2.6 hr.) despite the presence of renal insufficiency. Treatment resulted in improvement in serum inflammatory markers and symptoms and was well-tolerated.

Cost-effectiveness of ceftolozane/tazobactam plus metronidazole versus piperacillin/tazobactam as initial empiric therapy for the treatment of complicated intra-abdominal infections based on pathogen distributions drawn from national surveillance data in the United States

BACKGROUND

The prevalence of antimicrobial resistance among gram-negative pathogens in complicated intra-abdominal infections (cIAIs) has increased. In the absence of timely information on the infecting pathogens and their susceptibilities, local or regional epidemiology may guide initial empirical therapy and reduce treatment failure, length of stay and mortality. The objective of this study was to assess the cost-effectiveness of ceftolozane/tazobactam + metronidazole compared with piperacillin/tazobactam in the treatment of hospitalized US patients with cIAI at risk of infection with resistant pathogens.

METHODS

We used a decision-analytic Monte Carlo simulation model to compare the costs and quality-adjusted life years (QALYs) of persons infected with nosocomial gram-negative cIAI treated empirically with either ceftolozane/tazobactam + metronidazole or piperacillin/tazobactam. Pathogen isolates were randomly drawn from the Program to Assess Ceftolozane/Tazobactam Susceptibility (PACTS) database, a surveillance database of non-duplicate bacterial isolates collected from patients with cIAIs in medical centers in the USA from 2011 to 2013. Susceptibility to initial therapy was based on the measured susceptibilities reported in the PACTS database determined using standard broth micro-dilution methods as described by the Clinical and Laboratory Standards Institute (CLSI).

RESULTS

Our model results, with baseline resistance levels from the PACTS database, indicated that ceftolozane/tazobactam + metronidazole dominated piperacillin/tazobactam, with lower costs ($44,226/patient vs. $44,811/patient respectively) and higher QALYs (12.85/patient vs. 12.70/patient, respectively). Ceftolozane/tazobactam + metronidazole remained the dominant choice in one-way and probabilistic sensitivity analyses.

CONCLUSIONS

Based on surveillance data, ceftolozane/tazobactam is more likely to be an appropriate empiric therapy for cIAI in the US. Results from a decision-analytic simulation model indicate that use of ceftolozane/tazobactam + metronidazole would result in cost savings and improves QALYs, compared with piperacillin/tazobactam.

Pharmacokinetics of piperacillin-tazobactam in plasma, peritoneal fluid and peritoneum of surgery patients, and dosing considerations based on site-specific pharmacodynamic target attainment

Piperacillin-tazobactam (PIP-TAZ) is commonly used to treat intraabdominal infections; however, its penetration into abdominal sites is unclear. A pharmacokinetic analysis of plasma, peritoneal fluid, and peritoneum drug concentrations was conducted to simulate dosing regimens needed to attain the pharmacodynamic target in abdominal sites. PIP-TAZ (4 g-0.5 g) was intravenously administered to 10 patients before abdominal surgery for inflammatory bowel disease. Blood, peritoneal fluid, and peritoneum samples were obtained at the end of infusion (0.5 h) and up to 4 h thereafter. PIP and TAZ concentrations were measured, both noncompartmental and compartmental pharmacokinetic parameters were estimated, and a simulation was conducted to evaluate site-specific pharmacodynamic target attainment. The mean peritoneal fluid:plasma ratios in the area under the drug concentration-time curve (AUC) were 0.75 for PIP and 0.79 for TAZ, and the mean peritoneal fluid:plasma ratios in the AUC were 0.49 for PIP and 0.53 for TAZ. The mean PIP:TAZ ratio was 8.1 at both peritoneal sites. The regimens that achieved a bactericidal effect with PIP (time above minimum inhibitory concentration [MIC] >50%) at both peritoneal sites were PIP-TAZ 4.5 g twice daily for an MIC of 8 mg/L, as well as 4.5 g three times daily, and 3.375 g four times daily for an MIC of 16 mg/L. These findings clarify the peritoneal pharmacokinetics of PIP-TAZ, and help consider the dosing regimens for intraabdominal infections based on site-specific pharmacodynamic target attainment.

Cost-effectiveness of ceftolozane/tazobactam compared with piperacillin/tazobactam as empiric therapy based on the in-vitro surveillance of bacterial isolates in the United States for the treatment of complicated urinary tract infections

Background

A challenge in the empiric treatment of complicated urinary tract infection (cUTI) is identifying the initial appropriate antibiotic therapy (IAAT), which is associated with reduced length of stay and mortality compared with initial inappropriate antibiotic therapy (IIAT). We evaluated the cost-effectiveness of ceftolozane/tazobactam compared with piperacillin/tazobactam (one of the standard of care antibiotics), for the treatment of hospitalized patients with cUTI.

Methods

A decision-analytic Monte Carlo simulation model was developed to compare the costs and effectiveness of empiric treatment with either ceftolozane/tazobactam or piperacillin/tazobactam in hospitalized adult patients with cUTI infected with Gram-negative pathogens in the US. The model applies the baseline prevalence of resistance as reported by national in-vitro surveillance data.

Results

In a cohort of 1000 patients, treatment with ceftolozane/tazobactam resulted in higher total costs compared with piperacillin/tazobactam ($36,413 /patient vs. $36,028/patient, respectively), greater quality-adjusted life years (QALYs) (9.19/patient vs. 9.13/patient, respectively) and an incremental cost-effectiveness ratio (ICER) of $6128/QALY. Ceftolozane/tazobactam remained cost-effective at a willingness to pay of $100,000 per QALY compared to piperacillin/tazobactam over a range of input parameter values during one-way and probabilistic sensitivity analysis.

Conclusions

Model results show that ceftolozane/tazobactam is likely to be cost-effective compared with piperacillin/tazobactam for the empiric treatment of hospitalized cUTI patients in the United States.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-017-2408-7) contains supplementary material, which is available to authorized users.

Improvement of Karmali Agar by Supplementation with Tazobactam for Detecting Campylobacter in Raw Poultry

In this study, Karmali agar was modified by adding tazobactam (T-Karmali agar) to suppress the growth of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli , which frequently contaminates raw poultry meat. By inoculating 30 Campylobacter spp. strains and 25 ESBL-producing E. coli strains onto Karmali agar and T-Karmali agar containing various concentrations of the antibacterial agent, we determined the optimum concentration of tazobactam to be 4 mg/liter. The Campylobacter spp. isolation rate on T-Karmali agar (13.3%) was higher than that on Karmali agar (8.3%), although the difference was not significant (P > 0.05). However, T-Karmali agar showed a significantly greater selectivity than Karmali agar, as evaluated by comparing the numbers of contaminated agar plates (20.8 versus 82.5%; P < 0.05) and the growth indexes (1.36 versus 2.83) of competing flora. The predominant competing flora on Karmali and T-Karmali agar were identified as ESBL-producing E. coli . Thus, T-Karmali agar might be effective for determining the real prevalence of Campylobacter in raw poultry and, especially, contamination with ESBL-producing E. coli .

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.

In vitro activity of ceftolozane/tazobactam against clinical isolates of Pseudomonas aeruginosa in the planktonic and biofilm states

Pseudomonas aeruginosa causes a variety of life-threatening infections, some of which are associated with planktonic and others with biofilm states. Herein, we tested the combination of the novel cephalosporin, ceftolozane, with the β-lactamase inhibitor, tazobactam, against planktonic and biofilm forms of 54 clinical isolates of P. aeruginosa, using cefepime as a comparator. MIC values were determined following Clinical and Laboratory Standards Institute (CLSI) guidelines. Minimum biofilm inhibitory concentration (MBIC) values were determined using biofilm-laden pegged lids incubated in antimicrobial challenge plates containing varying concentrations of ceftolozane/tazobactam. Pegged lids were then incubated in growth recovery plates containing cation-adjusted Mueller-Hinton broth to determine the minimum biofilm bactericidal concentration (MBBC). Ceftolozane/tazobactam was highly active against planktonic P. aeruginosa, with all 54 isolates studied testing susceptible (MIC ≤4/4μg/mL). On the other hand, 51/54 biofilm P. aeruginosa had MBICs ≥16/4μg/mL, and all 54 isolates had MBBCs >32μg/mL. Of the 54 isolates, 45 (83.3%) tested susceptible to cefepime, with the MIC50/MIC90 being 4/16μg/mL, respectively, and the MBIC90 and MBBC90 both being >256μg/mL. Although ceftolozane/tazobactam is a promising antimicrobial agent for the treatment of P. aeruginosa infections, it is not highly active against P. aeruginosa biofilms.

Quantification of piperacillin, tazobactam, meropenem, ceftazidime, and linezolid in human plasma by liquid chromatography/tandem mass spectrometry

Therapeutic drug monitoring is a cornerstone of antibacterial therapy, especially in an era of increasing antibacterial resistance in individualizing antimicrobial therapy. Liquid chromatography/tandem mass spectrometry (LC-MS/MS) assay was used for the simultaneous measurement of piperacillin, tazobactam, meropenem, ceftazidime, and linezolid in 50 μl plasma samples over a wide range. The overall turnaround time for the assay was 20 minutes. Intra-assay precision and accuracy for quality control samples ranged within 1·8-8·5 and 91·4-106·7%, respectively. Inter-assay precision and accuracy ranged within 1·3-14·4 and 95·8-104·6%, respectively. The lower limit of quantification was below 1·5 μg/ml for all the five antibiotics. No ion suppression due to matrix effects was found. A simple and rapid LC-MS/MS method which provides high specificity, precision and accuracy for the simultaneous quantification of piperacillin, tazobactam, meropenem, ceftazidime, and linezolid in human plasma has been developed and validated. The present method is suitable for therapeutic drug monitoring in paediatrics.

Cross-Canada survey of resistance of 2747 aerobic blood culture isolates to piperacillin/tazobactam and other antibiotics

OBJECTIVE

To compare the activity of piperacillin/tazobactam with that of other broad parenteral antibiotics against aerobic and facultative anaerobic blood culture isolates in a Canada-wide survey.

DESIGN

Fifty-eight laboratories in nine provinces each contributed up to 50 consecutive clinically significant aerobic and facultative anaerobic isolates for susceptibility testing.

SETTING

Participating hospitals included both tertiary care and community hospitals.

MATERIALS AND METHODS

Testing was performed in five regional centres by using the same microbroth dilution method, and results were interpreted according to National Commitee for Clinical Laboratory Standards M7-A3 and M100-S5 guidelines.

RESULTS

Piperacillin/tazobactam and imipenem were both active against more than 99% of the 1616 strains of Enterobacteriaceae species tested. The minimum inhibitory concentration of 90% of isolates (MIC(90)) of all Enterobacteriaceae species was 2 mg/L for piperacillin/tazobactam compared with 64 mg/L for piperacillin alone. Seventeen per cent of strains of Enterobacteriaceae species were susceptible to piperacillin/tazobactam but resistant to piperacillin. Piperacillin/tazobactam was highly active against Pseudomonas aeruginosa, inhibiting 99.1% of strains. MIC(90) was 8 mg/L. Nine per cent of P aeruginosa strains were not susceptible to imipenem. Most of these strains had a MIC of 8 mg/L, which falls in the intermediate category. Ninety-seven per cent of P aeruginosa were susceptible to ciprofloxacin and 97.3% to tobramycin. Ninety-six per cent of strains of Actinobacter species were susceptible to piperacillin/tazobactam, whereas only 76% of strains were susceptible to piperacillin alone. Overall, piperacillin/tazobactam was the most active agent tested; 98% of all strains were susceptible, followed closely by imipenem, to which 97.8% of strains were susceptible.

CONCLUSIONS

Aerobic blood culture isolates from Canadian centres continue to be highly susceptible to a variety of antibiotics. The broad spectrum of activity of piperacillin/tazobactam suggests that this combination should be considered for empirical treatment of sepsis while awaiting results of cultures and susceptibility testing.