Evaluation and implementation of optimized antimicrobial dosing strategies in obese and underweight patients.

PURPOSE: We aimed to develop and implement dosing recommendations for antimicrobials in obese and underweight patients within an academic hospital, and assess their impact on antibiotic prescribing. METHODS: A multi-step approach project was performed. First, obese and underweight patient prevalence and antimicrobial prescription frequency was determined in a point prevalence study. Second and third, a literature review and e-survey provided dosing evidence. Fourth, a consensus meeting was organized to formulate dosing recommendations. Fifth, these were implemented in our clinical validation service as six clinical rules continuously screening patients' records for potentially inappropriate prescriptions (PIPs). Uptake was evaluated by documenting the number of advices and acceptance rate. Last, an interrupted time series analysis (ITS) compared pre- and post-implementation periods to measure the impact of the intervention on residual PIPs/day. A residual PIP was defined as a PIP which persisted up to 48 h. RESULTS: First, 41% of 15.896 hospitalized patients received antimicrobials over 20 days; of which 12% were obese and 9% underweight. Antibiotics were predominantly prescribed according to standard dosing regimens, adjusted to renal function. Next, six dosing recommendations, derived from literature, survey, and consensus, were implemented. In the fifth step, during an 18-week period, 219 advices were given, with 86% acceptance rate. Last, in the ITS analysis, at preintervention, a median of 75% residual PIPs/day existed, reduced to 0% postintervention. Use of clinical rules resulted in a significant immediate 84% relative reduction in residual PIPs (95% CI 0.55-0.94). CONCLUSION: After conducting a literature review, e-survey, and seeking consensus from a panel of experts, dosing recommendations for antimicrobial treatment in both obese and underweight patients were developed. These recommendations have been successfully implemented into clinical practice, addressing the specific needs of these patient populations.

Check of APpropriaTeness of Antimicrobial therapy In Nursing homes (CAPTAIN):a point prevalence study in Belgium.

Objectives: The overall prevalence of antimicrobial therapy (AMT) in nursing homes is well described. However, less is known about the appropriateness of AMT in nursing home residents. Therefore, the Check of APpropriaTeness of antimicrobial therapy in nursing homes (CAPTAIN) study aimed to assess both prevalence and appropriateness of AMT in Belgian nursing homes. Methods: In a prospective, observational, point prevalence study, researchers documented prevalence and identified potentially inappropriate prescriptions (PIPs) by evaluating accordance of AMT with national guidelines. The severity of inappropriateness was assessed by a modified Delphi expert panel. Results: Eleven nursing homes, including 1178 residents, participated in this study. On the survey day, 8.0% of residents took systemic AMT, primarily for urinary tract infections (54.2%), respiratory tract infections (36.5%), and skin and skin-structure infections (6.3%). About half of these prescriptions were used in prophylaxis (52.1%). Registration of indication and stop date was missing in 58.3% and 56.3% of AMTs, respectively. In 89.6% of the systemic AMTs, at least one discordance with national guidelines was identified, resulting in a total of 171 PIPs, with 49 unique PIPs. Of all unique PIPs, 26.5% were assessed with a high severity score (≥4). According to the expert panel, most inappropriate practice was starting AMT for cough without other symptoms. Inappropriate timing of time-dependent AMTs was common, but assessed as 'moderately severe'. One-third of systemic AMT exceeded the recommended duration. Conclusions: AMT in nursing homes is often not prescribed according to national guidelines, highlighting the need for future interventions to promote the rational use of AMT in this setting.

Dosing of IV posaconazole to treat critically ill patients with invasive pulmonary aspergillosis: a population pharmacokinetics modelling and simulation study.

BACKGROUND: Posaconazole is used for the prophylaxis and treatment of invasive fungal infections in critically ill patients. Standard dosing was shown to result in adequate attainment of the prophylaxis Cmin target (0.7 mg/L) but not of the treatment Cmin target (1.0 mg/L). OBJECTIVES: To provide an optimized posaconazole dosing regimen for IV treatment of patients with invasive pulmonary aspergillosis in the ICU. METHODS: A population pharmacokinetics (popPK) model was developed using data from the POSA-FLU PK substudy (NCT03378479). Monte Carlo simulations were performed to assess treatment Cmin and AUC0-24 PTA. PTA ≥90% was deemed clinically acceptable. PopPK modelling and simulation were performed using NONMEM 7.5. RESULTS: Thirty-one patients with intensive PK sampling were included in the PK substudy, contributing 532 posaconazole plasma concentrations. The popPK of IV posaconazole was best described by a two-compartment model with linear elimination. Interindividual variability was estimated on clearance and volume of distribution in central and peripheral compartments. Posaconazole peripheral volume of distribution increased with bodyweight. An optimized loading regimen of 300 mg q12h and 300 mg q8h in the first two treatment days achieved acceptable PTA by Day 3 in patients <100 kg and ≥100 kg, respectively. A maintenance regimen of 400 mg q24h ensured ≥90% Cmin PTA, whereas the standard 300 mg q24h was sufficient to achieve the AUC0-24 target throughout 14 days, irrespective of bodyweight. CONCLUSIONS: We have defined a convenient, optimized IV posaconazole dosing regimen that was predicted to attain the treatment target in critically ill patients with invasive aspergillosis.

Evaluation of environmental antibiotic contamination by surface wipe sampling in a large care centre.

OBJECTIVES: Exposure of healthcare workers to antibiotics may cause adverse health effects. Results of environmental contamination with antibiotics, obtained by taking surface wipe samples, can be used as an indicator for potential exposure to these sensitizing drugs. The objective was to describe the results of repeated measurements of contamination with antibiotics on multiple surfaces in hospital wards. Standardized needle and syringe preparation techniques and cleaning procedures were used. METHODS: The preparation table and the floor around the waste bin in six wards were sampled and analysed for contamination with the antibiotics amoxicillin, benzylpenicillin, cefotaxime, ceftriaxone, flucloxacillin, meropenem, piperacillin and vancomycin. Sampling was performed in four trials during 8 months. Depending on the outcome of the trials, the cleaning procedure was adapted. Liquid chromatography with tandem mass spectrometry was used for the analysis of the drugs. RESULTS: During the four trials, contamination with all eight antibiotics was omnipresent on all preparation tables and floors in the six wards. The highest contamination was found for amoxicillin (1291 ng/cm2). Changing the cleaning procedure did not reduce the level of contamination. CONCLUSIONS: Surface contamination with the antibiotics was widespread and most probably caused by spillage during the preparation in combination with an ineffective cleaning procedure. Strategies should be developed and implemented by institutions for safe handling of antibiotics to reduce environmental contamination and potential exposure of healthcare workers to these sensitizing drugs.

Personalized Antifungal Therapy Through Model-Informed Precision Dosing of Posaconazole.

BACKGROUND AND OBJECTIVE: Posaconazole is a pharmacotherapeutic pillar for prophylaxis and treatment of invasive fungal diseases. Dose individualization is of utmost importance as achieving adequate antifungal exposure is associated with improved outcome. This study aimed to select and evaluate a model-informed precision dosing strategy for posaconazole. METHODS: Available population pharmacokinetic models for posaconazole administered as a solid oral tablet were extracted from the literature and evaluated using data from a previously published prospective study combined with data collected during routine clinical practice. External evaluation and selection of the most accurate and precise model was based on graphical goodness-of-fit and predictive performance. Measures for bias and imprecision included mean percentage error (MPE) and normalized relative root mean squared error (NRMSE), respectively. Subsequently, the best-performing model was evaluated for its a posteriori fit-for-purpose and its suitability in a limited sampling strategy. RESULTS: Seven posaconazole models were evaluated using 764 posaconazole plasma concentrations from 143 patients. Multiple models showed adequate predictive performance illustrated by acceptable goodness-of-fit and MPE and NRMSE below ± 10% and ± 25%, respectively. In the fit-for-purpose analysis, the selected model showed adequate a posteriori predictive performance. Bias and imprecision were lowest in the presence of two prior measurements. Additionally, this model showed to be useful in a limited sampling strategy as it adequately predicted total posaconazole exposure from one (non-)trough concentration. CONCLUSION: We validated an MIPD strategy for posaconazole for its fit-for-purpose. Thereby, this study is an important first step towards MIPD-supported posaconazole dosage optimization with the goal to improve antifungal treatment in clinical practice.

Agreement Between a Colorimetric Assay and Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry for Quantifying Paracetamol Plasma Concentrations.

Special populations, like geriatric patients, experience altered paracetamol pharmacokinetics (PK), complicating pain management. More PK research is essential to optimize paracetamol (acetaminophen) dosing. Yet, the reference method ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) is not readily available. Therefore, we aimed to evaluate the agreement between UPLC-MS/MS and the more accessible colorimetric Roche acetaminophen (ACETA) assay in quantifying paracetamol plasma concentrations, to facilitate PK studies and therapeutic drug monitoring for pain management. Patient data and plasma samples were obtained from a prospective study including geriatric patients admitted to the geriatric wards. ACETA and UPLC-MS/MS assays were performed in two separate laboratories. Bland-Altman plot and Passing-Bablok regression were used to assess agreement. Accuracy was evaluated using the McNemar test for a threshold value of 10 mg/L. Population PK modeling was employed to bridge PK data obtained from both methods (NONMEM 7.5). A total of 242 plasma sample pairs were available from 40 geriatric patients (age range, 80-95 years). Paracetamol plasma concentrations from ACETA (median 9.8 [interquartile range 6.1-14.4] mg/L) and UPLC-MS/MS (9.5 [6.2-14.8] mg/L) did not differ significantly (P > 0.05). No significant proportional nor additive bias was observed between both assay methods. The classification accuracy (at threshold 10 mg/L) was 85% (P = 0.414). The conversion factor between ACETA and UPLC-MS/MS was estimated at 1.06 (relative standard error 5%), yet with a 13.4% (relative standard error 23%) interindividual variability. ACETA assay showed no systematic bias in comparison with the UPLC-MS/MS assay in determining paracetamol exposure in geriatric blood samples despite the imprecision.

Ceftazidime-related neurotoxicity in a patient with renal impairment: a case report and literature review.

PURPOSE: We present the case of a 67-year-old woman with severely reduced renal clearance suffering from ceftazidime-induced encephalopathy. Subsequently, we search the literature to review and describe the neurotoxicity of ceftazidime. METHODS: A search string was developed to search PubMed for relevant cases from which relevant information was extracted. Using the collected data a ROC analysis was performed in R to determine a neurotoxicity threshold. RESULTS: Our patient suffered from progressive loss of consciousness and myoclonic seizures, with improvements noted a few days after discontinuation of treatment. The dose was not appropriately reduced to take into account her reduced renal function. The highest ceftazidime concentration recorded was 234.9 mg/mL. Using the Naranjo score we found a probable relationship between our patient's encephalopathy and ceftazidime administration. In the literature we found a total of 32 similar cases, most of which also had some form of renal impairment. Using our collected data and ceftazidime concentrations provided in the literature, a ROC analysis provided a neurotoxicity threshold of 78 mg/L for ceftazidime neurotoxicity. CONCLUSION: Ceftazidime-related neurotoxicity is a known issue, especially in patients with severe renal impairment. Yet no concrete toxicity threshold has been reported so far. We propose the first toxicity threshold for ceftazidime of 78 mg/L. Future prospective studies are needed to validate and optimize the neurotoxicity threshold as upper limit for ceftazidime therapeutic drug monitoring.

Medication use in a cohort of adults with chronic intestinal failure: A prospective cross-sectional study.

BACKGROUND: Oral drug therapy may be compromised in chronic intestinal failure (IF) because of alterations in absorption and transit. Only scarce literature is available on which medication patients with chronic IF take in daily life. The aim was to describe the medication use in these patients. METHODS: A medication history was obtained from adults with chronic IF treated in our tertiary care IF center. Degree of polypharmacy, drug classes, Biopharmaceutics Classification System classes, route of administration, and formulation of drugs were analyzed. RESULTS: From October 2019 until December 2020, 72 patients (35 patients with short bowel syndrome [SBS] and 37 patients without SBS) were included. Polypharmacy was seen in 85.7% of patients with SBS and 75.7% of patients without SBS. The top three drug classes were proton-pump inhibitors, vitamin D or acetaminophen, and antimotility medication or laxatives/benzodiazepines. Approximately 25% of the drugs were classified as Biopharmaceutics Classification System class I drugs. In patients with SBS (78%) and patients without SBS (74.9%), most medication was taken orally, requiring gastrointestinal absorption of the active substance to be pharmacologically active. Most of these medications (77% in patients with SBS and 80.8% in patients without SBS) were formulated as a capsule or tablet, requiring disintegration and dissolution in the gastrointestinal tract before absorption can take place. CONCLUSION: Polypharmacy was observed in most patients with chronic IF. Most medication was taken orally in formulations requiring disintegration, dissolution, and gastrointestinal absorption, which could be compromised in chronic IF.

High Burden of COVID-19-Associated Pulmonary Aspergillosis in Severely Immunocompromised Patients Requiring Mechanical Ventilation.

BACKGROUND: Coronavirus disease 2019 (COVID-19)-associated pulmonary aspergillosis (CAPA) is a frequent superinfection in critically ill patients with COVID-19 and is associated with increased mortality rates. The increasing proportion of severely immunocompromised patients with COVID-19 who require mechanical ventilation warrants research into the incidence and impact of CAPA during the vaccination era. METHODS: We performed a retrospective, monocentric, observational study. We collected data from adult patients with severe COVID-19 requiring mechanical ventilation who were admitted to the intensive care unit (ICU) of University Hospitals Leuven, a tertiary referral center, between 1 March 2020 and 14 November 2022. Probable or proven CAPA was diagnosed according to the 2020 European Confederation for Medical Mycology/International Society for Human and Animal Mycology (ECMM/ISHAM) criteria. RESULTS: We included 335 patients. Bronchoalveolar lavage sampling was performed in 300 (90%), and CAPA was diagnosed in 112 (33%). The incidence of CAPA was 62% (50 of 81 patients) in European Organisation for Research and Treatment of Cancer (EORTC)/Mycosis Study Group Education and Research Consortium (MSGERC) host factor-positive patients, compared with 24% (62 of 254) in host factor-negative patients. The incidence of CAPA was significantly higher in the vaccination era, increasing from 24% (57 of 241) in patients admitted to the ICU before October 2021 to 59% (55 of 94) in those admitted since then. Both EORTC/MSGERC host factors and ICU admission in the vaccination era were independently associated with CAPA development. CAPA remained an independent risk factor associated with mortality risk during the vaccination era. CONCLUSIONS: The presence of EORTC/MSGERC host factors for invasive mold disease is associated with increased CAPA incidence and worse outcome parameters, and it is the main driver for the significantly higher incidence of CAPA in the vaccination era. Our findings warrant investigation of antifungal prophylaxis in critically ill patients with COVID-19.

Development of quality indicators for antimicrobial stewardship in Belgian hospitals: a RAND - modified Delphi procedure.

INTRODUCTION: Inappropriate antibiotic use is a major cause of antibiotic resistance. Therefore, optimizing antibiotic usage is essential. In Belgium, optimization of antimicrobials for the fight against multidrug resistant organisms (MDROs) is followed up by national surveillance by public health authorities. To improve appropriate antimicrobial use in hospitals, an effective national Antimicrobial Stewardship (AMS) program should include indicators for measuring both the quantity and quality of antibiotic use. OBJECTIVES: The aim of this study was to develop a set of process quality indicators (QIs) to evaluate and improve AMS in hospitals. METHODS: A RAND-modified Delphi procedure was used. The procedure consisted of a structured narrative literature review to select the QIs, followed by two online questionnaires and an intermediate multidisciplinary panel discussion with experts in infectious diseases from general and teaching hospitals in Belgium. RESULTS: A total of 38 QIs were selected after the RAND-modified Delphi procedure, from which 11 QIs were selected unanimously. These QIs address compliancy of antibiotic therapy and prophylaxis with local guidelines, documentation of the rationale for antibiotic treatment in the medical record, the availability of AMS Programs and Outpatient Parenteral Antibiotic Therapy, resistance patterns and antimicrobial prescribing during focused ward rounds. CONCLUSION: Our study selected 38 relevant process QIs, from which 11 were unanimously selected. The QIs can contribute to the improvement of quality of antibiotic use by stimulating hospitals to present better outcomes and by providing a focus on how to intervene and to improve prescribing of antimicrobials.

Predicting Beta-Lactam Target Non-Attainment in ICU Patients at Treatment Initiation: Development and External Validation of Three Novel (Machine Learning) Models.

In the intensive care unit (ICU), infection-related mortality is high. Although adequate antibiotic treatment is essential in infections, beta-lactam target non-attainment occurs in up to 45% of ICU patients, which is associated with a lower likelihood of clinical success. To optimize antibiotic treatment, we aimed to develop beta-lactam target non-attainment prediction models in ICU patients. Patients from two multicenter studies were included, with intravenous intermittent beta-lactam antibiotics administered and blood samples drawn within 12-36 h after antibiotic initiation. Beta-lactam target non-attainment models were developed and validated using random forest (RF), logistic regression (LR), and naïve Bayes (NB) models from 376 patients. External validation was performed on 150 ICU patients. We assessed performance by measuring discrimination, calibration, and net benefit at the default threshold probability of 0.20. Age, sex, serum creatinine, and type of beta-lactam antibiotic were found to be predictive of beta-lactam target non-attainment. In the external validation, the RF, LR, and NB models confirmed good discrimination with an area under the curve of 0.79 [95% CI 0.72-0.86], 0.80 [95% CI 0.73-0.87], and 0.75 [95% CI 0.67-0.82], respectively, and net benefit in the RF and LR models. We developed prediction models for beta-lactam target non-attainment within 12-36 h after antibiotic initiation in ICU patients. These online-accessible models use readily available patient variables and help optimize antibiotic treatment. The RF and LR models showed the best performance among the three models tested.

Longitudinal evaluation of environmental contamination with hazardous drugs by surface wipe sampling.

INTRODUCTION: Exposure of healthcare workers to hazardous drugs can lead to adverse health effects supporting the importance of a continuous monitoring program, for example, by taking surface wipe samples. The objective was to describe the results of repeated monitoring of contamination with hazardous drugs on multiple surfaces in a hospital pharmacy and at two wards using standardized preparation techniques and cleaning procedures. METHODS: Twelve surfaces in the hospital pharmacy and at two wards were sampled and analyzed for contamination with the hazardous drugs cyclophosphamide, doxorubicin, 5-fluorouracil, gemcitabine, methotrexate, and paclitaxel. The drugs were prepared with a closed-system drug transfer device (CSTD). Sampling of the drugs was performed in four trials during eight months. Liquid chromatography tandem mass spectrometry was used for the analysis of the drugs. RESULTS: During the four trials, contamination with five of the six hazardous drugs was found on half of the surfaces in the pharmacy and in a ward. Seventeen out of 288 possible outcomes were positive (6%), with the biological safety cabinet grate (n = 6) and scanner (n = 5) most frequently contaminated. The highest level of contamination was observed on the pass-thru window (cyclophosphamide: 2.90 ng/cm2) and the touch screen of the Diana device (5-fluorouracil: 2.38 ng/cm2). Both levels were below the action level of 10 ng/cm2. CONCLUSIONS: The long-term use of a CSTD in combination with appropriate cleaning has proven effective in achieving low levels of surface contamination with hazardous drugs.

Bedside check of medication appropriateness (BED-CMA) as a risk-based tool for bedside clinical pharmacy services: A proof-of-concept study at the trauma surgery ward.

Background: Bedside clinical pharmacy prevents drug-related problems, but is not feasible in many countries due to limited resources. Hence, clinical rules using structural information in the electronic health record can help identifying potentially inappropriate prescriptions (PIPs). We aimed to develop and implement a risk-based clinical pharmacy service and evaluate its impact on prescribing at the trauma surgery ward. Methods: The proportion of residual PIPs per day, i.e. the number of PIPs that persisted up to 24 h after pharmacist intervention divided by the number of PIPs at T0, was evaluated before and after implementation of the intervention in an interrupted time series analysis. The pre-intervention cohort received usual pharmacy services, i.e. a 0.3 FTE clinical pharmacist trainee. Fifteen clinical rules, targeting antimicrobial, anticoagulant and analgesic therapy were implemented in the post-intervention period. The pre-intervention period was compared to two post-intervention scenarios: A) clinical rule alerts reviewed by a 0.3 FTE clinical pharmacist trainee; and B) clinical rule alerts reviewed daily for approximately 1 h by a clinical pharmacist trainee. Results: Pre-intervention, a median proportion of 67% (range 0%-100%) residual PIPs per day was observed. Scenario A showed an immediate relative reduction of 14% (p = 0.72) and scenario B a significant immediate relative reduction of 85% (p = 0.0015) in residual PIPs per day. In scenario A, recommendations were provided for 19% of clinical rule alerts, of which 67% was accepted by the surgeon within 24 h. In scenario B, recommendations were given for 56% of alerts, of which 84% was accepted. Conclusions: Using clinical rules is an effective approach to organize bedside clinical pharmacy services and improves prescribing at the trauma surgery ward. Advanced training and daily follow-up of the clinical rules are two requirements to be considered.

Stability of magistral phage preparations before therapeutic application in patients with chronic rhinosinusitis, sepsis, pulmonary, and musculoskeletal infections.

IMPORTANCE: As antimicrobial resistance becomes more prevalent, the application of (bacterio)phage therapy as an alternative treatment for difficult-to-treat infections is (re)gaining popularity. Over the past decade, numerous promising case reports and series have been published demonstrating the therapeutic potential of phage therapy. However, important questions remain regarding the optimal treatment protocol and, unlike for medicinal products, there are currently no predefined quality standards for the stability of phage preparations. Phage titers can be influenced by several factors which could lead to reduced titers after preparation and storage and, ultimately, subtherapeutic applications. Determining the stability of different phages in different recipients according to the route of administration is therefore one of the first important steps in establishing a standardized protocol for phage therapy.

Population Pharmacokinetics of Total and Unbound Isavuconazole in Critically Ill Patients: Implications for Adaptive Dosing Strategies.

BACKGROUND AND OBJECTIVES: Isavuconazole is a broad-spectrum antifungal agent for the management of invasive fungal disease. Optimised drug exposure is critical for patient outcomes, specifically in the critically ill population. Solid information on isavuconazole pharmacokinetics including protein binding in patients in the intensive care unit is scarce. We aimed to describe the total and unbound isavuconazole pharmacokinetics and subsequently propose a dosage optimisation strategy. METHODS: A prospective multi-centre study in adult intensive care unit patients receiving isavuconazole was performed. Blood samples were collected on eight timepoints over one dosing interval between days 3-7 of treatment and optionally on one timepoint after discontinuation. Total and unbound isavuconazole pharmacokinetics were analysed by means of population pharmacokinetic modelling using NONMEM. The final model was used to perform simulations to assess exposure described by the area under the concentration-time curve and propose an adaptive dosing approach. RESULTS: Population pharmacokinetics of total and unbound isavuconazole were best described by an allometrically scaled two-compartment model with a saturable protein-binding model and interindividual variability on clearance and the maximum binding capacity. The median (range) isavuconazole unbound fraction was 1.65% (0.83-3.25%). After standard dosing, only 35.8% of simulated patients reached a total isavuconazole area under the concentration-time curve > 60 mg·h/L at day 14. The proposed adaptive dosing strategy resulted in an increase to 62.3% of patients at adequate steady-state exposure. CONCLUSIONS: In critically ill patients, total isavuconazole exposure is reduced and protein binding is highly variable. We proposed an adaptive dosing approach to enhance early treatment optimisation in this high-risk population. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT04777058.

Isavuconazole Exposure in Critically Ill Patients Treated with Extracorporeal Membrane Oxygenation: Two Case Reports and a Narrative Literature Review.

Effective dosing of isavuconazole in patients supported by extracorporeal membrane oxygenation (ECMO) is important due to the role of isavuconazole as a first-line treatment in patients with influenza- and COVID-19-associated pulmonary aspergillosis. To date, robust pharmacokinetic data in patients supported by ECMO are limited. Therefore, it is unknown whether ECMO independently impacts isavuconazole exposure. We measured isavuconazole plasma concentrations in two patients supported by ECMO and estimated individual pharmacokinetic parameters using non-compartmental analysis and two previously published population pharmacokinetic models. Furthermore, a narrative literature review on isavuconazole exposure in adult patients receiving ECMO was performed. The 24 h areas under the concentration-time curve and trough concentrations of isavuconazole were lower in both patients compared with exposure values published before. In the literature, highly variable isavuconazole concentrations have been documented in patients with ECMO support. The independent effect of ECMO versus critical illness itself on isavuconazole exposure cannot be deduced from our and previously published (case) reports. Pending additional data, therapeutic drug monitoring is recommended in critically ill patients, regardless of ECMO support.

Unravelling the Hepatic Elimination Mechanisms of Colistin.

PURPOSE: Colistin is an antibiotic which is increasingly used as a last-resort therapy in critically-ill patients with multidrug resistant Gram-negative infections. The purpose of this study was to evaluate the mechanisms underlying colistin's pharmacokinetic (PK) behavior and to characterize its hepatic metabolism. METHODS: In vitro incubations were performed using colistin sulfate with rat liver microsomes (RLM) and with rat and human hepatocytes (RH and HH) in suspension. The uptake of colistin in RH/HH and thefraction of unbound colistin in HH (fu,hep) was determined. In vitro to in vivo extrapolation (IVIVE) was employed to predict the hepatic clearance (CLh) of colistin. RESULTS: Slow metabolism was detected in RH/HH, with intrinsic clearance (CLint) values of 9.34± 0.50 and 3.25 ± 0.27 mL/min/kg, respectively. Assuming the well-stirred model for hepatic drug elimination, the predicted rat CLh was 3.64± 0.22 mL/min/kg which could explain almost 70% of the reported non-renal in vivo clearance. The predicted human CLh was 91.5 ± 8.83 mL/min, which was within two-fold of the reported plasma clearance in healthy volunteers. When colistin was incubated together with the multidrug resistance-associated protein (MRP/Mrp) inhibitor benzbromarone, the intracellular accumulation of colistin in RH/HH increased significantly. CONCLUSION: These findings indicate the major role of hepatic metabolism in the non-renal clearance of colistin, while MRP/Mrp-mediated efflux is involved in the hepatic disposition of colistin. Our data provide detailed quantitative insights into the hereto unknown mechanisms responsible for non-renal elimination of colistin.