Target Attainment Rates Research Articles

A multicentric, randomized, controlled clinical trial to study the impact of bedside model-informed precision dosing of vancomycin in critically ill children—BENEFICIAL trial

BackgroundVancomycin is a commonly prescribed antibiotic to treat serious Gram-positive infections in children. The efficacy of vancomycin is known to be directly related to the pharmacokinetic/pharmacodynamic (PK/PD) index of the area under the concentration–time curve (AUC) divided by the minimal inhibitory concentration (MIC) of the pathogen. In most countries, steady-state plasma concentrations are used as a surrogate parameter for this target AUC/MIC, but this practice has some drawbacks. Hence, AUC-based dosing using model-informed precision dosing (MIPD) tools has been proposed for increasing the target attainment rate and reducing vancomycin-related nephrotoxicity. Solid scientific evidence for these claimed benefits is lacking in children. This randomized controlled trial aims to investigate the large-scale utility of MIPD dosing of vancomycin in critically ill children.MethodsParticipants from 14 neonatal intensive care, pediatric intensive care, and pediatric hemo-oncology ward units from 7 hospitals are randomly allocated to the intervention or standard-of-care comparator group. In the intervention group, a MIPD dosing calculator is used for AUC-based dosing, in combination with extra sampling for therapeutic drug monitoring in the first hours of treatment, as compared to standard-of-care. An AUC24h between 400 and 600 is targeted, assuming an MIC of 1 mg/L. Patients in the comparator group receive standard-of-care dosing and monitoring according to institutional guidelines. The primary endpoint is the proportion of patients reaching the target AUC24h/MIC of 400–600 between 24 and 48 h after the start of vancomycin treatment. Secondary endpoints are the proportion of patients with (worsening) acute kidney injury during vancomycin treatment, the proportion of patients reaching target AUC24h/MIC of 400–600 between 48 and 72 h after the start of vancomycin treatment, time to clinical cure, ward unit length-of-stay, hospital length-of-stay, and 30-day all-cause mortality.DiscussionThis trial will clarify the propagated benefits and provide new insights into how to optimally monitor vancomycin treatment in critically ill children.Trial registrationEudract number: 2019–004538-40. Registered on 2020–09-08ClinicalTrials.gov NCT046666948. Registered on 2020–11-28

Therapeutic drug monitoring-guided piperacillin dosing in critically ill patients undergoing continuous renal replacement therapy: a systematic review.

Continuous renal replacement therapy (CRRT) complicates antibiotic dosing in critically ill patients due to altered pharmacokinetics. The optimal dosing of piperacillin remains unclear. Therapeutic drug monitoring (TDM) can personalize piperacillin therapy and improve outcomes. This review investigates the effects of TDM-guided piperacillin dosing on pharmacokinetic target attainment and clinical outcomes in CRRT patients, analyses correlations with clinical outcomes, provides optimal dosing strategies for piperacillin and identifies future research areas. A systematic search of PubMed, Scopus and Web of Science was conducted until December 2023, identifying studies on piperacillin pharmacokinetics and clinical outcomes in adult CRRT patients. Data on study characteristics, piperacillin exposures, TDM use, target attainment rates, mortality and length of stay were extracted. The risk of bias was assessed using the Newcastle-Ottawa Scale. Eleven observational studies were included. High pharmacokinetic variability was evident, with piperacillin target non-attainment in up to 74% of cases without TDM. Two studies with routine TDM showed increased target attainment rates of 80%-100%. Mortality ranged from 17% to 56%, with supratherapeutic concentrations (≥100 mg/L) associated with higher mortality. The impact of optimized piperacillin exposures on outcomes was inconclusive. Most studies demonstrated a low risk of bias. TDM-guided piperacillin dosing in CRRT patients improved target attainment rates (≥80%). Mortality rates ranged from 17% to 56%, with inconsistent correlations between drug exposures and survival. Supratherapeutic concentrations were linked to higher mortality. Standardized TDM protocols are needed. Future research should establish clear exposure-response relationships and the impact of TDM on clinical outcomes.

Pharmacokinetics and pharmacodynamics of two in-feed chlortetracycline regimens provided to beef cattle.

Plasma chlortetracycline (CTC) concentration data were subjected to Monte Carlo simulation of area under the concentration curve (AUC) values related to bovine respiratory disease pathogen MIC distributions to evaluate target attainment rates. Crossbred Hereford heifers were randomly assigned into two treatment groups. Treatment group (A) received chlortetracycline (CTC) at a target dose of 22 mg/kg of bodyweight daily for 5 consecutive days (n = 8) and group (B) received CTC at 350 mg/head per day (1.5 ± 0.2 mg/kg based on actual bodyweights) for seven consecutive days (n = 8). Non-compartmental analysis was used to calculate plasma-free drug CTC area under the concentration curves. The mean observed (±SD) free drug AUC values were 4.18 (±1.72) μg × h/mL and 0.30 (±0.06) μg × h/mL for treatment groups A and B, respectively. The probability of target attainment for AUC24/MIC values of 25 and 12.5 was modeled using Monte Carlo simulations. Treatment group A achieved >90% target attainment (AUC24/MIC of 25) at an MIC of 0.06 μg/mL, whereas treatment group B displayed only 12.6% target attainment (AUC24/MIC of 12.5) at the lowest MIC evaluated (0.015 μg/mL). Both in-feed CTC regimens failed to obtain a reasonable target attainment rate in light of expected MIC distributions of potential pathogens.

Association between prolonged vancomycin infusion and trough concentrations in children. Retrospective study.

Introduction: This study investigated the serum concentration of vancomycin during prolonged infusion in children. Population and methods: This retrospective cohort study included pediatric patients who received vancomycin from June 2017 to June 2020 at a tertiary referral hospital. The patients were divided into two groups according to infusion strategy, the SII (standard intermittent infusion) group and the PI (prolonged infusion) group. Demographic details, infusion period, serum creatinine, duration of vancomycin therapy, trough concentration of vancomycin, and pediatric intensive care unit stay were reviewed. Differences of the concentrations were measured. Results: Sixty-eight patients were included: 31 in the SII group and 37 in the PI group. The trough concentration of vancomycin was significantly higher in the PI group than in SII group (11.2 mg/L [5.9-13.7] vs. 7 mg/L [3.5- 9.3]; p = 0.02). The target attainment rate was higher in the PI group than in the SII group (59.4% and 19.3%, respectively; p = 0.001). There were no significant differences between the SII and PI groups regarding the peak concentrations of vancomycin, final creatinine and peak creatinine. There were no differences between the SII and PI groups regarding the failure events, PICU stay and duration of vancomycin therapy. The multivariable analysis showed that PI was significantly associated with higher trough serum concentrations of vancomycin (OR = 2.27; p = 0.005). Conclusion: Compared to the SII strategy, the PI strategy may be an optimized option to children with severe infection, as it can achieve higher trough concentrations and target concentration attainment.

The effect of audit and feedback and implementation support on guideline adherence and patient outcomes in cardiac rehabilitation: a study protocol for an open-label cluster-randomized effectiveness-implementation hybrid trial

Background Providing secondary prevention through structured and comprehensive cardiac rehabilitation programmes to patients after a myocardial infarction (MI) reduces mortality and morbidity and improves health-related quality of life. Cardiac rehabilitation has the highest recommendation in current guidelines. While treatment target attainment rates at Swedish cardiac rehabilitation centres is among the highest in Europe, there are considerable differences in service delivery and variations in patient-level outcomes between centres. In this trial, we aim to study whether centre-level guideline adherence and patient-level outcomes across Swedish cardiac rehabilitation centres can be improved through a) regular audit and feedback of cardiac rehabilitation structure and processes through a national quality registry and b) supporting cardiac rehabilitation centres in implementing guidelines on secondary prevention. Furthermore, we aim to evaluate the implementation process and costs.MethodsThe study is an open-label cluster-randomized effectiveness-implementation hybrid trial including all 78 cardiac rehabilitation centres (attending to approximately 10 000 MI patients/year) that report to the SWEDEHEART registry. The centres will be randomized 1:1:1 to three clusters: 1) reporting cardiac rehabilitation structure and process variables to SWEDEHEART every six months (audit intervention) and being offered implementation support to implement guidelines on secondary prevention (implementation support intervention); 2) audit intervention only; or 3) no intervention offered. Baseline cardiac rehabilitation structure and process variables will be collected. The primary outcome is an adherence score measuring centre-level adherence to secondary prevention guidelines. Secondary outcomes include patient-level secondary prevention risk factor goal attainment at one-year after MI and major adverse coronary outcomes for up to five-years post-MI. Implementation outcomes include barriers and facilitators to guideline adherence evaluated using semi-structured focus-group interviews and relevant questionnaires, as well as costs and cost-effectiveness assessed by a comparative health economic evaluation.DiscussionOptimizing cardiac rehabilitation centres’ delivery of services to meet standards set in guidelines may lead to improvement in cardiovascular risk factors, including lifestyle factors, and ultimately a decrease in morbidity and mortality after MI.Trial registrationClinicalTrials.gov. Identifier: NCT05889416. Registered 2023-03-23.

Optimization of Ganciclovir and Valganciclovir Starting Dose in Children by Machine Learning.

Ganciclovir (GCV) and valganciclovir (VGCV) show large interindividual pharmacokinetic variability, particularly in children.The objectives of this study were (1) to develop machine learning (ML) algorithms trained on simulated pharmacokinetics profiles obtained by Monte Carlo simulations to estimate the best gancicloviror valganciclovirstarting dose in children and (2) to compare its performances on real-world profiles to previously published equation derived from literature population pharmacokinetic (POPPK) models achieving about 20% of profiles within the target. The pharmacokinetic parameters of four literature POPPK models in addition to the World Health Organization (WHO) growth curve for children were used in the mrgsolve R package to simulate 10,800 pharmacokinetic profiles. ML algorithms were developed and benchmarked to predict the probability to reach the steady-state, area-under-the-curve target (AUC0-24within 40-60 mg × h/L) based on demographic characteristics only. The best ML algorithm was then used to calculate the starting dose maximizing the target attainment. Performances were evaluated for ML and literature formula in a test set and in an external set of 32 and 31 actual patients (GCV and VGCV, respectively). A combination of Xgboost, neural network, and random forest algorithms yielded the best performances and highest target attainment in the test set (36.8% for GCV and 35.3% for the VGCV). In actual patients, the best GCV ML starting dose yielded the highest target attainment rate (25.8%) and performed equally for VGCV with the Franck model formula (35.3% for both). The ML algorithms exhibit good performances in comparison with previously validated models and should be evaluated prospectively.

Impact of the PK/PD Approach in Therapeutic Drug Monitoring of Gentamicin

Gentamicin, a commonly used hospital aminoglycoside, exhibits a narrow therapeutic index, necessitating careful administration to prevent serious adverse effects. Our study aimed to assess the impact of Therapeutic drug Monitoring (TDM) by integrating Minimum Inhibitory Concentration (MIC) to customize dosage based on bacterial sensitivity. This was prospective study, conducted on a sample of 35 adult patients hospitalized in three university hospital centers in Eastern Algeria. Included patients underwent Therapeutic Drug Monitoring (TDM) of gentamicin based on the determination of Maximum concentration (Cmax), considering the determination of the MIC and achieving a Cmax/CMI ratio ≥ 8 to 10. Pharmaceutical interventions were suggested to clinicians to improve patient care. The mean age of our patients was 51.66 ± 16.72 years. All patients had Cmax values below the therapeutic range. Pathogenic microorganisms were identified in 64% of cases, and only two patients achieved the Cmax/CMI target of 8 to 10 prior to our interventions. In 41% of cases, clinicians heeded our guidance on regular therapeutic monitoring and dose adjustments. The therapeutic target was achieved in 66.6% of cases, with a Cmax/CMI target attainment rate of 44.4%.The use of individualized initial doses of gentamicin, combined with Therapeutic Drug Monitoring based on PK/PD parameters, enhances the chances of therapeutic success and restricts the emergence of bacterial resistance.

Implementing treat-to-target urate-lowering therapy during hospitalizations for gout flares.

To evaluate a strategy designed to optimize care and increase uptake of urate-lowering therapy (ULT) during hospitalizations for gout flares. We conducted a prospective cohort study to evaluate a strategy that combined optimal in-hospital gout management with a nurse-led, follow-up appointment, followed by handover to primary care. Outcomes, including ULT initiation, urate target attainment and re-hospitalization rates, were compared between patients hospitalized for flares in the 12 months post-implementation and a retrospective cohort of hospitalized patients from 12 months pre-implementation. One hundred and nineteen and 108 patients, respectively, were hospitalized for gout flares in the 12 months pre- and post-implementation. For patients with 6-month follow-up data available (n = 94 and n = 97, respectively), the proportion newly initiated on ULT increased from 49.2% pre-implementation to 92.3% post-implementation (age/sex-adjusted odds ratio [aOR] 11.5; 95% CI 4.36, 30.5; P < 0.001). After implementation, more patients achieved a serum urate ≤360 μmol/l within 6 months of discharge (10.6% pre-implementation vs 26.8% post-implementation; aOR 3.04; 95% CI 1.36, 6.78; P = 0.007). The proportion of patients re-hospitalized for flares was 14.9% pre-implementation vs 9.3% post-implementation (aOR 0.53; 95% CI 0.22, 1.32; P = 0.18). Over 90% of patients were initiated on ULT after implementing a strategy to optimize hospital gout care. Despite increased initiation of ULT during flares, recurrent hospitalizations were not more frequent following implementation. Significant relative improvements in urate target attainment were observed post-implementation; however, for the majority of hospitalized gout patients to achieve urate targets, closer primary-secondary care integration is still needed.

Patients who suffer a first atherosclerotic cardiovascular event while taking statins are often far off of lipid targets

Background and aimsDespite considerable evidence that lipid-lowering therapies (LLTs) afford clinical benefit, the control of low-density lipoprotein cholesterol (LDL-C) is suboptimal, and available LLTs are underused, especially in patients at high and very high cardiovascular (CV) risk. This study assesses the real-world LDL-C target attainment rate in patients on LLT before experiencing a first major acute cardiovascular event (MACE). Methods and resultsThe HEARTBEAT was a retrospective, multicentre observational study. From March to June 2021 a total of 334 patients on LLT who had a first MACE while being on statins were included in the study. Of these patients, 83.2 % had a high (40.7 %) or very high CV risk (29.0 %) prior to MACE. Overall, 87.5 % and 89.7 % of the patients at high and very high CV risk, respectively, failed to reach the LDL-C target. Regarding LLTs, only 11.8 % and 19.6 % of the patients at high and very high risk had received high-intensity LLTs prior to MACE. It was estimated that if these patients had reached their recommended LDL-C targets, the risk of MACE may have been reduced by a median of 24.5 % and 23.2 % in patients at high and very high risk respectively. ConclusionsPatients who suffer a first MACE while on statin therapy often were at high/very high CV risk. Despite their risk, LDL-levels and being on statins they are undertreated, and too far from lipid targets. A proper use of high-intensity LLTs led to an increase attainment of LDL targets and lower CV events.

Vancomycin and daptomycin dosing recommendations in patients receiving home hemodialysis using Monte Carlo simulation

BackgroundFew drug dosing recommendations for patients receiving home hemodialysis (HHD) have been published which has hindered the adoption of HHD. HHD regimens vary widely and differ considerably from conventional, thrice weekly, in-center hemodialysis in terms of treatment frequency, duration and blood and dialysate flow rates. Consequently, vancomycin and daptomycin clearances in HHD are also likely to be different, consequently HHD dosing regimens must be developed to ensure efficacy and minimize toxicity when these antibiotics are used. Many HHD regimens are used clinically, this study modeled ten common HHD regimens and determined optimal vancomycin and daptomycin dosing for each HHD regimen.MethodsMonte Carlo simulations using pharmacokinetic data derived from the literature and demographic data from a large HHD program treating patients with end stage kidney disease were incorporated into a one-compartment pharmacokinetic model. Virtual vancomycin and daptomycin doses were administered post-HHD and drug exposures were determined in 5,000 virtual patients receiving ten different HHD regimens. Serum concentration monitoring with subsequent dose changes was incorporated into the vancomycin models. Pharmacodynamic target attainment rates were determined for each studied dose. The lowest possible doses that met predefined targets in virtual patients were chosen as optimal doses.ResultsHHD frequency, total dialysate volumes and HHD durations influenced drug exposure and led to different dosing regimens to meet targets. Antibiotic dosing regimens were identified that could meet targets for 3- and 7-h HHD regimens occurring every other day or 4–5 days/week. HHD regimens with 3-day interdialytic periods required higher doses prior to the 3-day period. The addition of vancomycin serum concentration monitoring allowed for calculation of necessary dosing changes which increased the number of virtual subjects meeting pharmacodynamic targets.ConclusionsDoses of vancomycin and daptomycin that will meet desired pharmacodynamic targets in HHD are dependent on patient and HHD-specific factors. Doses used in conventional thrice weekly hemodialysis are unlikely to meet treatment goals. The antibiotic regimens paired with the HHD parameters studied in this analysis are likely to meet goals but require clinical validation.

Impact of model-informed precision dosing on achievement of vancomycin exposure targets in pediatric patients with cystic fibrosis.

Vancomycin is commonly used to treat acute pulmonary exacerbations in pediatric patients with cystic fibrosis (CF) and a history of methicillin-resistant Staphylococcus aureus. Optimizing vancomycin exposure during therapy is essential and area under-the-curve (AUC)-guided dosing is now recommended. Model-informed precision dosing (MIPD) utilizing Bayesian forecasting is a powerful approach that can support AUC-guided dose individualization. The objective of the current study was to examine the impact of implementing an AUC-guided dose individualization approach supported via a MIPD clinical decision support (CDS) tool on vancomycin exposure, target attainment rate, and safety in pediatric patients with CF treated with vancomycin during clinical care. A retrospective chart review was performed in patients with CF at a single children's hospital comparing pre- and post-implementation of a MIPD approach for vancomycin supported by a cloud-based, CDS tool integrated into the electronic health record (EHR). In the pre-MIPD period, vancomycin starting doses of 60 mg/kg/day (<13 years) or 45 mg/kg/day (≥13 years) were used. Dose adjustment was guided by therapeutic drug monitoring (TDM) with a target trough 10-20 mg/L. In the post-MIPD period, starting dose and dose adjustment were based on the MIPD CDS tool predictions with a target 24 h AUC (AUC24 ) 400-600 mg*h/L. Exposure and target achievement rates were retrospectively calculated and compared. Rates of acute kidney injury (AKI) were also compared. Overall, 23 patient courses were included in the pre-MIPD period and 21 patient courses in the post-MIPD period. In the post-MIPD period, an individualized MIPD starting dose resulted in 71% of patients achieving target AUC24 compared to 39% in the pre-MIPD period (p < 0.05). After the first TDM and dose adjustment, target AUC24 achievement was also higher post-MIPD versus pre-MIPD (86% vs. 57%; p < 0.05). AKI rates were low and similar between periods (pre-MIPD 8.7% vs. post-MIPD 9.5%; p = 0.9). An MIPD approach implemented within a cloud-based, EHR-integrated CDS tool safely supported vancomycin AUC-guided dosing and resulted in high rates of target achievement.

Population pharmacokinetic analysis and dosing optimization of polymyxin B in critically ill patients.

Objectives: Since the global broadcast of multidrug-resistant gram-negative bacteria is accelerating, the use of Polymyxin B is sharply increasing, especially in critically ill patients. Unsatisfactory therapeutic effects were obtained because of the abnormal physiological function in critically ill patients. Therefore, the determination of optimal polymyxin B dosage becomes highly urgent. This study aimed to illustrate the polymyxin B pharmacokinetic characteristics by defining the influencing factors and optimizing the dosing regimens to achieve clinical effectiveness. Methods: Steady-state concentrations of polymyxin B from twenty-two critically ill patients were detected by a verified liquid chromatography-tandem mass spectrometry approach. The information on age, weight, serum creatinine, albumin levels, and Acute Physiology and Chronic Health Evaluation-II (APACHE-II) score was also collected. The population PK parameters were calculated by the non-parametric adaptive grid method in Pmetrics software, and the pharmacokinetic/pharmacodynamics target attainment rate was determined by the Monte Carlo simulation method. Results: The central clearance and apparent volume of distribution for polymyxin B were lower in critically ill patients (1.24 ± 0.38Lh-1 and 16.64 ± 12.74 L, respectively). Moreover, albumin (ALB) levels can be used to explain the variability in clearance, and age can be used to describe the variability in the apparent volume of distribution. For maintaining clinical effectiveness and lowering toxicity, 75mg q12h is the recommended dosing regimen for most patients suffering from severe infections. Conclusion: This study has clearly defined that in critically ill patients, age and ALB levels are potentially important factors for the PK parameters of polymyxin B. Since older critically ill patients tend to have lower ALB levels, so higher dosages of polymyxin B are necessary for efficacy.

P793 Infliximab and prevention of colectomy in acute severe ulcerative colitis: an individual patient data meta-analysis

Abstract Background Infliximab (IFX) is used to treat patients with acute severe ulcerative colitis (ASUC) who fail to respond to intravenous corticosteroid therapy. Yet, a significant proportion of patients does not respond adequately and requires colectomy. Our aim was to explore baseline predictors of colectomy-free survival during IFX rescue therapy in patients with steroid-refractory ASUC. Methods We performed an individual patient data meta-analysis (IPDMA) with data retrospectively collected from hospitalised, corticosteroid-refractory patients diagnosed with ASUC (based on Truelove and Witts’ criteria) who received IFX rescue therapy. Baseline characteristics including sex, smoking status, disease extent, disease duration, Mayo endoscopic subscore, serum albumin, C-reactive protein, haemoglobin, and white blood count were evaluated as predictors of colectomy-free survival at three and twelve months after start of IFX therapy. Data were analysed using R software (v4.2.0). Results Data were collected from six centres contributing a total of 140 patients (Table 1). Fifteen patients (10.7%) required colectomy within three months and another eight patients underwent colectomy by one year (total colectomy rate after one year 16.4%) (Figure 1). No baseline predictors of colectomy-free survival were identified (log-rank P&amp;gt;0.05). Patients who received intensified IFX induction therapy (n=64, &amp;gt;5 mg/kg), in contrast to patients on regular induction doses of 5 mg/kg at weeks 0-2-6 (n=49), did not have lower rates of colectomy. A total of 53 IFX serum trough concentrations (TC) were measured in 31 patients. The median IFX TC during weeks (w)1-2 of therapy was 13.5 mg/L (interquartile range [IQR] 9.3-16.3 mg/L), and 7.0 (IQR 1.9-12.0) mg/L during w3-6. Target attainment rates were 8.3% (1/12 patients) and 18.2% (2/11 patients), respectively, towards the previously reported IFX TC targets of 28.3 mg/L at w2 and 15.0 mg/L at w6 for achieving endoscopic remission at w12.1 IFX TCs during induction were not significantly different between patients who received standard and intensified induction therapy. Conclusion Colectomy rates remain a significant burden of ASUC even for patients receiving IFX. In our interim IPDMA, we did not identify baseline predictors of colectomy-free survival. Poor target attainments of the previously established concentration targets demand dose optimisation. Pharmacometrics modelling of the IFX dose-exposure-biomarker/measure-response relationship within the spECTRUM consortium (DEFINE study) will facilitate dose-finding simulations to demonstrate the value of model-informed therapeutic drug monitoring.

Predictive Performance of Physiologically Based Pharmacokinetic Modelling of Beta-Lactam Antibiotic Concentrations in Adipose, Bone, and Muscle Tissues.

Physiologically based pharmacokinetic (PBPK) models consist of compartments representing different tissues. As most models are only verified based on plasma concentrations, it is unclear how reliable associated tissue profiles are. This study aimed to assess the accuracy of PBPK-predicted beta-lactam antibiotic concentrations in different tissues and assess the impact of using effect site concentrations for evaluation of target attainment. Adipose, bone, and muscle concentrations of five beta-lactams (piperacillin, cefazolin, cefuroxime, ceftazidime, and meropenem) in healthy adults were collected from literature and compared with PBPK predictions. Model performance was evaluated with average fold errors (AFEs) and absolute AFEs (AAFEs) between predicted and observed concentrations. In total, 26 studies were included, 14 of which reported total tissue concentrations and 12 unbound interstitial fluid (uISF) concentrations. Concurrent plasma concentrations, used as baseline verification of the models, were fairly accurate (AFE: 1.14, AAFE: 1.50). Predicted total tissue concentrations were less accurate (AFE: 0.68, AAFE: 1.89). A slight trend for underprediction was observed but none of the studies had AFE or AAFE values outside threefold. Similarly, predictions of microdialysis-derived uISF concentrations were less accurate than plasma concentration predictions (AFE: 1.52, AAFE: 2.32). uISF concentrations tended to be overpredicted and two studies had AFEs and AAFEs outside threefold. Pharmacodynamic simulations in our case showed only a limited impact of using uISF concentrations instead of unbound plasma concentrations on target attainment rates. The results of this study illustrate the limitations of current PBPK models to predict tissue concentrations and the associated need for more accurate models. SIGNIFICANCE STATEMENT: Clinical inaccessibility of local effect site concentrations precipitates a need for predictive methods for the estimation of tissue concentrations. This is the first study in which the accuracy of PBPK-predicted tissue concentrations of beta-lactam antibiotics in humans were assessed. Predicted tissue concentrations were found to be less accurate than concurrent predicted plasma concentrations. When using PBPK models to predict tissue concentrations, this potential relative loss of accuracy should be acknowledged when clinical tissue concentrations are unavailable to verify predictions.

Pharmacokinetics and Target Attainment of ß-lactam Antibiotics in Older People: A Systematic Review of Current Literature

(Patho)physiological changes in older people may influence the pharmacokinetics (PK), and consequently the target attainment, of ß-lactam antibiotics using standard dosing regimens. This systematic review compiles the current knowledge on the PK and target attainment of ß-lactam antibiotics in older people, with the aim to identify priorities for dose optimization in this patient population. A systematic literature search of the PubMed and EMBASE databases was conducted. Relevant articles published prior to 1 December 2021 were identified as eligible when they included data on the PK of ß-lactam antibiotics in adults ≥65 years of age. Extracted information included reported PK parameters (volume of distribution, clearance [CL], elimination rate constant, intercompartmental CL, elimination half-life, area under the concentration-time curve, maximum and trough concentration), covariates on PK parameters, target attainment rate, and dosing recommendations. Ninety-one relevant articles were included in this review. Four main ß-lactam subclasses were represented: 59.3% on cephalosporins + cephamycins, 25.3% on penicillins, 15.4% on carbapenems, and 3.3% on monobactams; 65.9% of articles involved intravenous administration, 16.5% mixed administration routes, 12.1% oral administration, and 5.5% intramuscular administration. The majority of studies had a small sample size, often did not include detailed information on the study population and methods, and were fairly old. CL was, on average, decreased, while elimination half-life was prolonged in aged subjects compared with young subjects. Volume of distribution was generally similar between age groups. Most studies identified renal function as the most important contributor to altered drug CL. In only 30.8% of the articles, target attainment was studied, and in 35.7% of these articles, target attainment was found to be suboptimal. Dosing recommendations were incorporated in 87.9% of articles. Studies frequently fail to provide an evidence-based dosing recommendation for this diverse patient population. Model-based PK studies that address both physiological and disease-related changes are urgently needed. This review identified gaps of knowledge to set priorities for further research.

748: EVALUATION OF ANTI-XA TARGET ATTAINMENT WITH PROPHYLACTIC ENOXAPARIN DOSING REGIMENS IN OBESITY

Introduction: Venous thromboembolism (VTE) is a common complication among hospitalized patients, especially among the critically ill. Obesity doubles the risk of a patient experiencing a VTE event during their hospitalization. To combat this increased risk pharmacologic prophylaxis with enoxaparin is commonly utilized. The optimal dosing strategy for enoxaparin in morbidly obese patients is currently unknown. Previous studies have demonstrated a negative correlation between body weight and anti-Xa activity and enoxaparin 40 mg daily resulted in subtherapeutic anti-Xa levels in 82% of patients. The objective of this study was to assess anti-Xa target attainment in patients receiving enoxaparin at a dose of 40 mg twice daily, 60 mg twice daily, or 0.5 mg/kg twice daily. Methods: This study was a single-center retrospective cohort study of critically ill patients with a BMI ≥ 40 kg/m2 receiving prophylactic enoxaparin at a dose of 40 mg twice daily, 60 mg twice daily, or 0.5 mg/kg twice daily. The primary outcome was attainment of a target anti-Xa level (0.2-0.5 IU/mL). Secondary outcomes included the incidence of VTE, major bleeding, subtherapeutic anti-Xa, and supratherapeutic anti-Xa. Results: Sixty-five patients were evaluated, and four patients were excluded. Twenty-eight patients received 40 mg twice daily, twenty-two patients received 60 mg twice daily, and eleven patients received 0.5 mg/kg twice daily. Target anti-Xa levels were achieved more often among patients receiving 0.5 mg/kg twice daily compared to both 60 mg twice daily and 40 mg twice daily (100% versus 59.1% versus 21.4%, p < 0.001). VTE was rare occurring in one patient receiving 60 mg twice daily. Major bleeding occurred in three patients, two were receiving 60 mg twice daily and one was receiving 40 mg twice daily. Conclusions: Among morbidly obese ICU patients, enoxaparin 0.5 mg/kg twice daily was associated with a significantly greater rate of anti-Xa target attainment. This indicates that an aggressive, weight-based dosing method may be optimal among morbidly obese critical care patients. Future studies are necessary to determine the impact of this dosing regimen on clinically relevant outcomes.

Antimicrobial Exposures in Critically Ill Patients Receiving Extracorporeal Membrane Oxygenation.

Rationale: Data suggest that altered antimicrobial concentrations are likely during extracorporeal membrane oxygenation (ECMO). Objectives: The primary aim of this analysis was to describe the pharmacokinetics (PKs) of antimicrobials in critically ill adult patients receiving ECMO. Our secondary aim was to determine whether current antimicrobial dosing regimens achieve effective and safe exposure. Methods: This study was a prospective, open-labeled, PK study in six ICUs in Australia, New Zealand, South Korea, and Switzerland. Serial blood samples were collected over a single dosing interval during ECMO for 11 antimicrobials. PK parameters were estimated using noncompartmental methods. Adequacy of antimicrobial dosing regimens were evaluated using predefined concentration exposures associated with maximal clinical outcomes and minimal toxicity risks. Measurements and Main Results: We included 993 blood samples from 85 patients. The mean age was 44.7 ± 14.4 years, and 61.2% were male. Thirty-eight patients (44.7%) were receiving renal replacement therapy during the first PK sampling. Large variations (coefficient of variation of ⩾30%) in antimicrobial concentrations were seen leading to more than fivefold variations in all PK parameters across all study antimicrobials. Overall, 70 (56.5%) concentration profiles achieved the predefined target concentration and exposure range. Target attainment rates were not significantly different between modes of ECMO and renal replacement therapy. Poor target attainment was observed across the most frequently used antimicrobials for ECMO recipients, including for oseltamivir (33.3%), piperacillin (44.4%), and vancomycin (27.3%). Conclusions: Antimicrobial PKs were highly variable in critically ill patients receiving ECMO, leading to poor target attainment rates. Clinical trial registered with the Australian New Zealand Clinical Trials Registry (ACTRN12612000559819).

Clinical utility of a model-based amoxicillin dosage regimen in neonates with early-onset sepsis.

Early-onset sepsis (EOS) is one of the most significant causes of morbidity and mortality in neonates. Currently, amoxicillin is empirically used to treat neonates with EOS. However, data on its effectiveness in neonates with EOS are still limited. Therefore, we aimed to evaluate the pharmacodynamics (PD) target attainment and effectiveness of a model-based amoxicillin dosage regimen in these neonates. We used a previously developed model and collected additional clinical data from the EOS neonates who used the model-based dosage regimen (25 mg/kg every 12 h). The primary outcomes were PD target attainment (free drug concentration above minimum inhibitory concentration during 70% of the dosing interval) and treatment failure rate. The secondary endpoints were length of amoxicillin treatment, duration of hospitalization etc. Seventy-five neonates (postmenstrual age 28.4-41.6wk) were enrolled. A total of 70 (93.3%) neonates reached their PD target using 1mg/L as the minimum inhibitory concentration breakpoint. The treatment failure rate was 10.7%.

Optimization of Vancomycin Initial Dose in Term and Preterm Neonates by Machine Learning.

Vancomycin is one of the antibiotics most used in neonates. Continuous infusion has many advantages over intermittent infusions, but no consensus has been achieved regarding the optimal initial dose. The objectives of this study were: to develop a Machine learning (ML) algorithm based on pharmacokinetic profiles obtained by Monte Carlo simulations using a population pharmacokinetic model (POPPK) from the literature, in order to derive the best vancomycin initial dose in preterm and term neonates, and to compare ML performances with those of an literature equation (LE) derived from a POPPK previously published. The parameters of a previously published POPPK model of vancomycin in children and neonates were used in the mrgsolve R package to simulate 1900 PK profiles. ML algorithms were developed from these simulations using Xgboost, GLMNET and MARS in parallel, benchmarked and used to calculate the ML first dose. Performances were evaluated in a second simulation set and in an external set of 82 real patients and compared to those of a LE. The Xgboost algorithm yielded numerically best performances and target attainment rates: 46.9% in the second simulation set of 400-600 AUC/MIC ratio vs. 41.4% for the LE model (p = 0.0018); and 35.3% vs. 28% in real patients (p = 0.401), respectively). The Xgboost model resulted in less AUC/MIC > 600, thus decreasing the risk of nephrotoxicity. The Xgboost algorithm developed to estimate the initial dose of vancomycin in term or preterm infants has better performances than a previous validated LE and should be evaluated prospectively.

Optimal dosing of enoxaparin in overweight and obese children.

Current enoxaparin dosing guidelines in children are based on total body weight. This is potentially inappropriate in obese children as it may overestimate the drug clearance. Current evidence suggests that obese children may require lower initial doses of enoxaparin, therefore the aim of this work was to characterise the pharmacokinetics of enoxaparin in obese children and to propose a more appropriate dosing regimen. Data from 196 unique encounters of 160 children who received enoxaparin treatment doses were analysed. Enoxaparin concentration was quantified using the chromogenic anti factor Xa (anti-Xa) assay. Patients provided a total of 552 anti-Xa samples. Existing published pharmacokinetic (PK) models were fitted and evaluated against our dataset using prediction-corrected visual predictive check plots (pcVPCs). A PK model was fitted using a nonlinear mixed-effects modelling approach. The fitted model was used to evaluate the current standard dosing and identify an optimal dosing regimen for obese children. Published models of enoxaparin pharmacokinetics in children did not capture the pharmacokinetics of enoxaparin in obese children as shown by pcVPCs. A one-compartment model with linear elimination best described the pharmacokinetics of enoxaparin. Allometrically scaled fat-free mass with an estimated exponent of 0.712 (CI 0.66-0.76) was the most influential covariate on clearance while linear fat-free mass was selected as the covariate on volume. Simulations from the model showed that fat-free mass-based dosing could achieve the target anti-Xa activity at steady state in 77.5% and 78.2% of obese and normal-weight children, respectively, compared to 65.2% and 75.5% for standard total body weight-based dosing. A population PK model that describes the time course of anti-Xa activity of enoxaparin was developed in a paediatric population. Based on this model, a unified dosing regimen was proposed that will potentially improve the success rate of target attainment in overweight/obese patients without the need for patient body size categorisation. Therefore, prospective validation of the proposed approach is warranted.