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BACKGROUND: Current guidelines recommend dosing vancomycin based on the area under the concentration time curve (AUC) to maximise efficacy and minimise the risk of nephrotoxicity. The preferred approach to AUC-guided therapy is to apply model-informed precision dosing (MIPD). However, the adoption in clinical practice has been slow.

AIM: We aimed to develop an intervention, including a standardised MIPD workflow and an implementation plan for vancomycin AUC-guided dosing, in a Swedish tertiary hospital.

METHOD: The intervention was developed in a framework-guided process. The design phase included stakeholder feedback (nurses, pharmacists, physicians), local data collection and feasibility testing of intervention components with parallel consideration of implementation aspects. The hypothesised relationships between the different components, implementation strategies and the mechanism of action resulting in expected outcomes were represented by a logic model.

RESULTS: The final intervention consisted of a workflow for MIPD, with defined roles and responsibilities, as well as processes for data and information transfer. Details were provided in supportive documents; an instruction on therapeutic drug monitoring (TDM) sampling and documentation for nurses, and a detailed dosing software instruction for MIPD consultants and clinical pharmacists. Activities to facilitate implementation included the development of a local clinical routine for vancomycin dosing, staff training and recurring MIPD rounds.

CONCLUSION: An intervention for MIPD, with an implementation plan for AUC-guided dosing of vancomycin, was developed for a tertiary hospital setting. The process can be used as guidance for other institutions with similar context wishing to initiate MIPD.

Background

Antibiotic heteroresistance is a common bacterial phenotype characterised by the presence of small resistant subpopulations within a susceptible population. During antibiotic exposure, these resistant subpopulations can be enriched and potentially lead to treatment failure. In this study, we examined the prevalence, misclassification, and clinical effect of heteroresistance in Escherichia coli bloodstream infections for the clinically important antibiotics cefotaxime, gentamicin, and piperacillin–tazobactam.

Methods

We conducted a retrospective cohort analysis of patients (n=255) admitted to in-patient care and treated for E coli bloodstream infections within the Uppsala region in Sweden between Jan 1, 2014, and Dec 31, 2015. Patient inclusion criteria were admission to hospital on suspicion of infection, starting systemic antibiotics at the time of admission, positive blood cultures for the growth of E coli upon admission, and residency in the Uppsala health-care region at the time of admission. Exclusion criteria were growth of an additional pathogen than E coli in blood cultures taken at admission or previous inclusion of the patients in the study for another bloodstream infection. Antibiotic susceptibility of preserved blood culture isolates of E coli was assessed for cefotaxime, gentamicin, and piperacillin–tazobactam by disk diffusion and breakpoint crossing heteroresistance (BCHR) was identified using population analysis profiling. The clinical outcome parameters were obtained from patient records. The primary outcome variable was length of hospital stay due to the E coli bloodstream infection, defined as the time between admission and discharge from inpatient care as noted on the physician’s notes. Secondary outcomes were time to fever resolution, admission to intermediary care unit or intensive care unit during time in hospital, switching or adding another intravenous antibiotic treatment, re-admission to hospital within 30 days of original admission, recurrent E coli infection within 30 days of admission to hospital, and all-cause mortality within 90 days of admission.

Findings

A total of 255 participants with a corresponding E coli isolate (out of 500 screened for eligibility) met the inclusion criteria, with 135 female patients and 120 male patients. One (<1%) of 255 strains was BCHR for cefotaxime, 109 (43%) of 255 strains were BCHR for gentamicin, and 22 (9%) of 255 strains were BCHR for piperacillin–tazobactam. Clinical susceptibility testing misclassified 120 (96%) of 125 heteroresistant bacterial strains as susceptible. The BCHR phenotypes had no correlation to length of hospital stay due to the E coli bloodstream infection. However, patients with piperacillin–tazobactam BCHR strains who received piperacillin–tazobactam had 3·1 times higher odds for admittance to the intermediate care unit (95% CI 1·1–9·6, p=0·041) than the remainder of the cohort, excluding those treated with gentamicin. Similarly, those infected with gentamicin BCHR who received gentamicin showed higher odds for admittance to the intensive care unit (5·6 [1·1–42·0, p=0·043]) and mortality (7·1 [1·2–49·2, p=0·030]) than patients treated with gentamicin who were infected with non-gentamicin BCHR E coli.

Interpretation

In a cohort of patients with E coli bloodstream infections, heteroresistance is common and frequently misidentified in routine clinical testing. Several negative effects on patient outcomes are associated with heteroresistant strains.

OBJECTIVES: This study aimed to predict the impact of different infusion strategies on pharmacokinetic/pharmacodynamic (PK/PD) target attainment and the potential risk for toxicity in an ICU cohort treated with β-lactams.

METHOD: Using collected patient data from 137 adult ICU patients, and applying population PK models, individual PK parameters were estimated and used to predict concentrations and target attainment following cefotaxime 2 g q8h, piperacillin/tazobactam 4.5 g q6h and meropenem 1 g q8h, applying 15 min short infusions (SI), 3 h extended infusions (EI) and 24 h continuous infusion (CI). The MIC level of the most common primary pathogens, and the worst-case scenario (WCS) pathogen, were used in analyses.

RESULTS: For primary pathogens, target was reached in 94% (129/137) using SI. For WCS pathogens treated with piperacillin/tazobactam and meropenem, 78% (65/83) and 92% (76/83) reached target using SI and EI, respectively. However, target attainment was lower for cefotaxime [SI: 31% (17/54), EI: 44% (24/54)]. Overall, the number of individuals with potentially toxic concentrations was low, both in EI (n = 7) and SI (n = 5). For CI and WCS, target was reached in 50% (27/54), 96% (54/56) and 93% (25/27) for cefotaxime, piperacillin/tazobactam and meropenem, respectively.

CONCLUSIONS: In a Swedish ICU cohort target attainment rates for primary pathogens were high regardless of infusion strategy. In WCS pathogens, SI was insufficient, suggesting the benefit of routine use of EI or CI. However, for cefotaxime, target attainment remained low also with EI and CI. The use of CI might lead to unnecessarily high concentrations, but well-established toxicity levels are lacking and future studies are warranted.

Estimated glomerular filtration rate (eGFR) based on creatinine (eGFR_Creatinine) or cystatin C (eGFR_CystatinC) require steady-state conditions and thus have limitations in intensive care unit (ICU) patients. Gentamicin is a potential exogenous marker for eGFR but poorly investigated. This retrospective study included adult ICU patients (≥ 18 years) treated with gentamicin and not on renal replacement therapy (RRT) at admission. eGFR_Creatinine and eGFR_CystatinC were calculated using the LM-rev and CAPA equations, respectively. Gentamicin clearance was estimated using a population pharmacokinetic model and used as eGFR_Gentamicin. Agreement between eGFRs vs. eGFR_Gentamicin and prediction of RRT and mortality for each eGFR were assessed. 254 patients were included of whom 11% (n = 28) received RRT later and 19% (n = 49) were dead at 30 days. The bias was 12 mL/min/1.73 m² and 8 mL/min/1.73 m², respectively, and the limits of agreement - 31-55 mL/min/1.73m² and - 46-62 mL/min/1.73m² for the agreement between eGFR_Gentamicin vs. eGFR_Creatinine, and for eGFR_Gentamicin vs. eGFR_CystatinC, respectively. The c-indexes for predicting RRT during ICU stay were 0.75 (0.64-0.86), 0.77 (0.66-0.88) and 0.80 (0.69-0.90) for eGFR_Creatinine, eGFR_CystatinC and eGFR_Gentamicin respectively, and for 30-day mortality 0.61 (0.52-0.70), 0.61 (0.52-0.70) and 0.63 (0.54-0.72) respectively. In ICU patients already receiving gentamicin, eGFR_Gentamicin derived from population PK models can be used to assess renal function and could potentially help improve dosing of other renally cleared drugs like the β-lactams during early phase of infections in the ICU.

We report for the first time a case of disseminated infection caused by Peziza ostracoderma, a mold not previously associated with invasive infections in humans. P. ostracoderma occurs in natural and sterilized soil and may cause hypersensitivity pneumonitis in greenhouse workers. The immunocompromised patient presented with neutropenic fever that did not respond to broad-spectrum antibiotics and developed multiple skin and lung lesions. A skin biopsy demonstrated an angioinvasive mold, identified as Peziza ostracoderma by culture and DNA sequencing. Minimum inhibitory concentration (MIC) for amphotericin B was 0.125 mg/L, for isavuconazole 0.125 mg/L, for voriconazole 0.06 mg/L, and for posaconazole 0.03 mg/L. The skin lesions have resolved completely, and the lung lesions have decreased significantly in size after 14 months of mold-active antifungal therapy, mostly isavuconazole. In conclusion, Peziza species can be opportunistic pathogens causing considerable morbidity in immunocompromised hosts. The infection may be successfully treated with mold-active antifungal drugs.

Objective: Abdominal aortic graft and endograft infections (AGIs) are rare complications following aortic surgery. Radical surgery (RS) with resection of the infected graft and reconstruction with extra-anatomical bypass or in situ reconstruction is the preferred therapy. For patients unfit for RS, a semi-conservative (SC), graft preserving strategy is possible. This paper aimed to compare survival and infection outcomes between RS and SC treatment for AGI in a nationwide cohort.

Methods: Patients with abdominal AGI related surgery in Sweden between January 1995 and May 2017 were identified. The Management of Aortic Graft Infection Collaboration (MAGIC) criteria were used for the definition of AGI. Multivariable regression was performed to identify factors associated with mortality.

Results: One hundred and sixty-nine patients with surgically treated abdominal AGI were identified, comprising 43 SC (14 endografts; 53% with a graft enteric fistula [GEF] in total) and 126 RS (26 endografts; 50% with a GEF in total). The SC cohort was older and had a higher frequency of cardiac comorbidities. There was a non-significant trend towards lower Kaplan -Meier estimated five year survival for SC vs. RS (30.2% vs. 48.4%; p = .066). A non-significant trend was identified towards worse Kaplan -Meier estimated five year survival for SC patients with a GEF vs. without a GEF (21.7% vs. 40.1%; p = .097). There were significantly more recurrent graft infections comparing SC with RS (45.4% vs. 19.3%; p < .001). In a Cox regression model adjusting for confounders, there was no difference in five year survival comparing SC vs. RS (HR 1.0, 95% CI 0.6 -1.5).

Conclusion: In this national AGI cohort, there was no mortality difference comparing SC and RS for AGI when adjusting for comorbidities. Presence of GEF probably negatively impacts survival outcomes of SC patients. Rates of recurrent infection remain high for SC treated patients.

Background

Therapeutic drug monitoring (TDM) has been suggested to optimize antimicrobial target attainment, typically using 100%T_>MIC, in β-lactam treatment in the ICU. The MIC parameter used in this equation is mostly the worst case scenario MIC (MIC_WCS)—the highest MIC the empirical treatment should cover. However, the impact of the MIC parameter used in pharmacokinetic/pharmacodynamic calculations has been poorly investigated.

Objectives

To assess the influence of target attainment rates for two different MIC parameters using actual MICs of the causative pathogens as the primary reference.

Methods

In a Swedish multicentre study of target attainment for 138 ICU patients treated with β-lactams, the causative pathogen was isolated and subjected to reference MIC testing. Whenever the strain belonged to the WT distribution, we assigned it to the category MIC_ECOFF (epidemiological cut-off value). In the calculations we compared the MIC_ECOFF and the MIC_WCS.

Results

The proportion of patients with target attainment failure for all antibiotics using 100%T_>MIC was 45% (95% CI, 37%–53%) for MIC_WCS and 23% (95% CI, 16%–31%) for MIC_ECOFF. When the target 50%T_>4×MIC was used, corresponding attainment failures were 57% (95% CI, 49%–66%) and 25% (95% CI, 17%–32%) for MIC_WCS and MIC_ECOFF, respectively.

Conclusions

MIC_WCS can overestimate target attainment failure. The use of MIC_WCS could be one reason for the difficulties in establishing a relationship between target failure and mortality in other studies. Based on findings herein, the MIC_ECOFF, which is based on the MIC of the causative pathogen, should be considered a more suitable alternative. When no pathogen is detected, the MIC_ECOFF of likely pathogens according to infection type should be used.

Background

Recent studies have shown low caspofungin concentrations in critically ill patients. In some patients, the therapeutic target, area under the total plasma concentration curve in relation to the minimal inhibition concentration (AUC_tot/MIC), seems not to be achieved and therapeutic drug monitoring (TDM) has been proposed. Caspofungin is highly protein-bound and the effect of reduced plasma protein levels on pharmacodynamics has not been investigated.

Objectives

Fungal killing activity of caspofungin in vitro was investigated under varying levels of human plasma protein.

Methods

Time-kill studies were performed with clinically relevant caspofungin concentrations of 1-9 mg/L on four blood isolates of C. glabrata, three susceptible and one strain with reduced susceptibility, in human plasma and plasma diluted to 50% and 25% using Ringer's acetate.

Results

Enhanced fungal killing of the three susceptible strains was observed in plasma with lower protein content (p < .001). AUC_tot/MIC required for a 1 log₁₀ CFU/ml kill at 24 h in 50% and 25% plasma was reduced with 36 + 12 and 80 + 9%, respectively. The maximum effect was seen at total caspofungin concentrations of 4–9 × MIC. For the strain with reduced susceptibility, growth was significantly decreased at lower protein levels.

Conclusions

Reduced human plasma protein levels increase the antifungal activity of caspofungin in vitro, most likely by increasing the free concentration. Low plasma protein levels in critically ill patients with candidemia might explain a better response to caspofungin than expected from generally accepted target attainment and should be taken into consideration when assessing TDM based on total plasma concentrations.

Severe infections are life-threatening conditions commonly seen in the intensive care units (ICUs). Antibiotic treatment with adequate concentrations is of great importance during the first days when the bacterial load is the highest. Therapeutic drug monitoring (TDM) of β-lactam antibiotics has been suggested to monitor target attainment and to improve the outcome. This prospective multi-center study in seven ICUs in Sweden investigated pharmacokinetic/pharmacodynamic-target (PK/PD-target) attainment for cefotaxime, piperacillin-tazobactam and meropenem, commonly used β-lactams in Sweden. A mid-dose and trough antibiotic concentration blood sample were taken from patients with severe infection daily during the first 72 h of treatment. Antibiotic plasma concentrations were analysed by liquid chromatography-mass spectrometry (LC–MS). Antibiotic concentrations 100% time above MIC (minimal inhibitory concentration), (100% T > MIC) and four times above MIC 50% of the time (50% T > 4xMIC) were used as PK/PD-targets. We included 138 patients with the median age of 67 years and the median Simplified Acute Physiology Score 3 (SAPS3) of 59. Forty-five percent of the study-population failed to reach 100% T > MIC during the first day of treatment. The results were similar the following two days. There was a three-fold risk of not meeting the PK/PD target if the patient was treated with cefotaxime. For the cefotaxime treated patients 8 out of 55 (15%) had at least one end-dose concentrations below the level of detection during the study. Low age, low illness severity, low plasma creatinine, lower respiratory tract infection and cefotaxime treatment were risk factors for not reaching 100% T > MIC. In Swedish ICU-patients treated with β-lactam antibiotics, a high proportion of patients did not reach the PK/PD target. TDM could identify patients that need individual higher dosing regimens already on the first day of treatment. Further studies on optimal empirical start dosing of β-lactams, especially for cefotaxime, in the ICU are needed.

PURPOSE: To characterise the pharmacokinetics and associated variability of cefotaxime in adult intensive care unit (ICU) patients and to assess the impact of patient covariates.

METHODS: This work was based on data from cefotaxime-treated patients included in the ACCIS (Antibiotic Concentrations in Critical Ill ICU Patients in Sweden) study. Clinical data from 51 patients at seven different ICUs in Sweden, given cefotaxime (1000-3000 mg given 2-6 times daily), were collected from the first day of treatment for up to three consecutive days. In total, 263 cefotaxime samples were included in the population pharmacokinetic analysis.

RESULTS: A two-compartment model with linear elimination, proportional residual error and inter-individual variability (IIV) on clearance and central volume of distribution best described the data. The typical individual was 64 years, with body weight at ICU admission of 92 kg and estimated creatinine clearance of 94 mL/min. The resulting typical value of clearance was 11.1 L/h, central volume of distribution 5.1 L, peripheral volume of distribution 18.2 L and inter-compartmental clearance 14.5 L/h. The estimated creatinine clearance proved to be a significant covariate on clearance (p < 0.001), reducing IIV from 68 to 49%.

CONCLUSION: A population pharmacokinetic model was developed to describe cefotaxime pharmacokinetics and associated variability in adult ICU patients. The estimated creatinine clearance partly explained the IIV in cefotaxime clearance. However, the remaining unexplained IIV is high and suggests a need for dose individualisation using therapeutic drug monitoring where the developed model, after evaluation of predictive performance, may provide support.