Outcomes of Drug Interactions Between Antiretrovirals and Co-Medications, Including Over-the-Counter Drugs: A Real-World Study.

INTRODUCTION: The objective was to characterize real-world outcomes of drug-drug interactions (DDIs) between antiretrovirals (ARVs) and other drugs, including over-the-counter medications (OTC), and treatment outcomes in clinical practice. METHODS: www.clinicalcasesDDIs.com is an open-access website for healthcare providers to consult and briefly describe real-world clinical cases on DDI with ARVs. We reviewed all the clinical cases reported to the website between March 2019 and May 2023. RESULTS: A total of 139 cases were reported, mostly involving ritonavir or cobicistat (boosters; 74 cases), unboosted integrase inhibitors (InSTI; 29 cases), and non-nucleoside reverse transcriptase inhibitors (NNRTI; 23 cases). Central nervous system drugs (29 cases) and cardiovascular drugs (19 cases) were the most frequently described co-medications. Notably, OTC medications were implicated in 27 cases, including mineral supplements (11 cases), herbals (8 cases), weight loss drugs (4 cases), anabolic steroids (3 cases), and recreational drugs (1 case). OTC acted as the perpetrator drug in 21 cases, leading to loss of ARV efficacy in 17 instances (mineral supplements in 10 cases, weight loss drugs in 4 cases, herbals in 3 cases). Additionally, toxicity was reported in 4 out of 6 cases where OTC was considered the victim drug of the DDI (anabolic steroids in 3 cases, MDMA in 1 case). CONCLUSIONS: Frequent unwanted outcomes resulting from DDIs between ARVs and OTC medications underscore the importance of integrating non-prescription drugs into medication reconciliation. The real-world data available through www.clinicalcasesDDIs.com serves as a valuable resource for assessing the clinical relevance of DDIs.

Stability Studies of Antipseudomonal Beta Lactam Agents for Outpatient Therapy.

Outpatient parenteral antimicrobial therapy (OPAT) is a useful treatment strategy against Pseudomonas aeruginosa and other multidrug-resistant bacteria. However, it is hindered by the lack of stability data for the administration of antibiotics under OPAT conditions. Our objective was to investigate the stability of nine antipseudomonal and broad-spectrum beta lactam antibiotics (aztreonam, cefepime, cefiderocol, ceftazidime, ceftazidime/avibactam, ceftolozane/tazobactam, meropenem, meropenem/vaborbactam, and piperacillin/tazobactam) to allow the spread of OPAT programs. All the antibiotics were diluted in 500 mL 0.9% sodium chloride and stored at 4, 25, 32, and 37 °C for 72 h in two different devices (infusion bags and elastomeric pumps). The solutions were considered stable if the color, clearness, and pH remained unchanged and if the percentage of intact drug was ≥90%. All the antimicrobials remained stable 72 h under refrigerated conditions and at least 30 h at 25 °C. At 32 °C, all the antibiotics except for meropenem and meropenem/vaborbactam remained stable for 24 h or more. At 37 °C, only aztreonam, piperacillin/tazobactam, cefepime, cefiderocol, and ceftolozane/tazobactam were stable for at least 24 h. The stability results were the same in the two devices tested. All the antibiotics studied are actual alternatives for the treatment of antipseudomonal or multidrug-resistant infections in OPAT programs, although the temperature of the devices is crucial to ensure antibiotic stability.

Colistin plasma concentrations are not associated with better clinical outcomes in patients with pneumonia caused by extremely drug-resistant Pseudomonas aeruginosa.

IMPORTANCE: In some cases, colistin is the only treatment option for infections caused by the very drug-resistant Pseudomonas aeruginosa. However, in the past decade, there have been questions concerning its pharmacokinetics and concentration at the site of infection. In this scenario, its use in a difficult-to-treat infection like pneumonia is currently debatable. This is a clinical pharmacokinetic study of colistin in patients with multidrug-resistant P. aeruginosa pneumonia. Our findings demonstrate that colistin exposure is associated with worse clinical outcomes rather than better clinical outcomes, implying that other therapeutic options should be explored in this clinical setting.

Agreement between pharmacists and physicians on the assessment of appropriateness of antimicrobial prescribing.

INTRODUCTION: Audits for monitoring the quality of antimicrobial prescribing are a main tool in antimicrobial stewardship programs; however, interobserver reliability has not been conclusively assessed. Our objective was to measure the level of agreement between pharmacists and physicians on the appropriateness of antimicrobials prescribing in hospitals. METHODS: A national multicenter, cross-sectional study was conducted of patients who were receiving antimicrobials one day of April 2021. Hospital participation was voluntary, and the study population was randomly selected. Pharmacists and physicians performed a simultaneous, independent assessment of the quality of antimicrobial prescriptions. The observers used an assessment method by which all indicators of the quality of antimicrobial use were considered. Finally, an algorithm was used to rate overall antimicrobial prescribing as appropriate, suboptimal, inappropriate, or not assessable. Gwet's AC1 coefficient was used to assess interobserver agreement. RESULTS: In total, 101 hospitals participated, and 411 hospital antimicrobial prescriptions were reviewed. The strength of agreement was moderate regarding the overall quality of prescribing (AC1=0.51; 95%CI=[0.44-0.58]). A very good level of agreement (AC1>0.80) was observed between pharmacists and physicians in all indicators of the quality, except for duration of treatment, rated as good (AC1=0.79; 95%CI=[0.75-0.83]), and registration on the medical record, rated as fair (AC1=0.34; 95%CI=[0.26-0.43]). The agreement was greater in critical care, onco-hematology, and pediatric units than in medical and surgery units. CONCLUSIONS: In this point prevalence study, a moderate level of agreement was observed between pharmacists and physicians in the evaluation of the appropriateness of antimicrobials prescribing in hospitals.

Clinical, Microbiological and Treatment Characteristics of Severe Postoperative Respiratory Infections: An Observational Cohort Study.

Respiratory infections are frequent and life-threatening complications of surgery. This study aimed to evaluate the clinical, microbiological and treatment characteristics of severe postoperative pneumonia (POP) and tracheobronchitis (POT) in a large series of patients. This single-center, prospective observational cohort study included patients with POP or POT requiring intensive care unit admission in the past 10 years. We recorded demographic, clinical, microbiological and therapeutic data. A total of 207 patients were included, and 152 (73%) were men. The mean (SD) age was 70 (13) years and the mean (SD) ARISCAT score was 46 (19). Ventilator-associated pneumonia was reported in 21 patients (10%), hospital-acquired pneumonia was reported in 132 (64%) and tracheobronchitis was reported in 54 (26%). The mean (SD) number of days from surgery to POP/POT diagnosis was 6 (4). The mean (SD) SOFA score was 5 (3). Respiratory microbiological sampling was performed in 201 patients (97%). A total of 177 organisms were cultured in 130 (63%) patients, with a high proportion of Gram-negative and multi-drug resistant (MDR) bacteria (20%). The most common empirical antibiotic therapy was a triple-drug regimen covering MDR Gram-negative bacteria and MRSA. In conclusion, surgical patients are a high-risk population with a high proportion of early onset severe POP/POT and nosocomial bacteria isolation.

Real-world experience of therapeutic drug monitoring and PK/PD achievement of ceftaroline administered by different infusion regimens in patients with confirmed infections caused by Gram-positive bacteria.

BACKGROUND: Ceftaroline is a novel cephalosporin active against MDR Gram-positive (GP) bacteria. For ß-lactam antibiotics, such as ceftaroline, prolonged infusions and therapeutic drug monitoring (TDM) are used for dosage optimization based on their pharmacokinetics/pharmacodynamics (PK/PD). OBJECTIVES: To describe our experience with TDM and PK/PD target attainment of ceftaroline administered by intermittent and prolonged infusion in a cohort of patients with MDR-GP bacterial infections. METHODS: Patients treated with ceftaroline administered by continuous (24 h), extended (3 h/6 h) and intermittent infusion (1 h) and undergoing TDM of plasma concentrations were included. A 100%fT>4×MIC was the pre-specified PK/PD target and 100%fT>10×MIC was considered overexposure. Dose recommendations were made based on TDM results and each patient's clinical condition. RESULTS: Twelve patients [83.3% male, median age of 73 (38-83) years] were included. Nine patients (75%) achieved 100%fT>4×MIC, all under prolonged infusions. In one patient, the 100%fT was >10×MIC but no toxicity was observed. Based on TDM results, initial doses were recommended to be maintained in eight patients, decreased in three and increased in one. CONCLUSIONS: The administration of ceftaroline by prolonged infusion together with TDM may be a useful strategy for achieving the desired PK/PD target in these patients. However, more studies evaluating the relationship between PK/PD attainment and clinical outcomes are needed.

Development and Validation of a Risk Score for Predicting Non-Adherence to Antiretroviral Therapy.

Several patient-related factors that influence adherence to antiretroviral therapy (ART) have been described. However, studies that propose a practical and simple tool to predict nonadherence after ART initiation are still scarce. In this study, we develop and validate a score to predict the risk of nonadherence in people starting ART. The model/score was developed and validated using a cohort of people living with HIV starting ART at the Hospital del Mar, Barcelona, between 2012 and 2015 (derivation cohort) and between 2016 and 2018 (validation cohort),. Adherence was evaluated every 2 months using both pharmacy refills and patient self-reports. Nonadherence was defined as taking <90% of the prescribed dose and/or ART interruption for more than 1 week. Predictive factors for nonadherence were identified by logistic regression. Beta coefficients were used to develop a predictive score. Optimal cutoffs were identified using the bootstrapping methodology, and performance was evaluated with the C statistic. Our study is based on 574 patients: 349 in the derivation cohort and 225 in the validation cohort. A total of 104 patients (29.8%) of the derivation cohort were nonadherent. Nonadherence predictors were patient prejudgment; previous medical appointment failures; cultural and/or idiomatic barriers; heavy alcohol use; substance abuse; unstable housing; and severe mental illness. The cutoff point (receiver operating characteristic curve) for nonadherence was 26.3 (sensitivity 0.87 and specificity 0.86). The C statistic (95% confidence interval) was 0.91 (0.87-0.94). These results were consistent with those predicted by the score in the validation cohort. This easy-to-use, highly sensitive, and specific tool could be easily used to identify patients at highest risk for nonadherence, thus allowing resource optimization and achieving optimal treatment goals.

Therapeutic Drug Monitoring of Vancomycin Concentrations for the Management of Bone and Joint Infections: An Urgent Need.

Vancomycin is used for the treatment of bone and joint infections (BJI), but scarce information is available about its pharmacokinetic/pharmacodynamic (PK/PD) characteristics. We aimed to identify the risk factors associated with the non-achievement of an optimal PK/PD target in the first therapeutic drug monitoring (TDM). Methods: A retrospective study was conducted in a tertiary hospital from January 2020 to January 2022. Patients with BJI and TDM of vancomycin on day 2 of treatment were included. Initial vancomycin fixed doses (1 g every 8 h or 12 h) was decided by the responsible doctors. According to TDM results, dosage adjustments were performed. An AUC24h/MIC < 400 mg × h/L, between 400 and 600 mg × h/L and >600 mg × h/L, were defined as suboptimal, optimal and supratherapeutic, respectively. Patients were grouped into these three categories. Demographic, clinical and PK characteristics were compared between groups. Nephrotoxicity at the end of treatment was assessed. Results: A total of 94 patients were included: 22 (23.4%), 42 (44.7%) and 30 (31.9%) presented an infratherapeutic, optimal and supratherapeutic PK/PD targets, respectively. A younger age and initial vancomycin dose <40 mg/kg/day were predictive factors for achieving a suboptimal PK/PD target, while older age, higher serum-creatinine and dose >40 mg/kg/day were associated with overexposure. The nephrotoxicity rate was 22.7%. More than 50% of patients did not achieve an optimal PK/PD. Considering age, baseline serum-creatinine and body weight, TDM is required to readily achieve an optimal and safe exposure.

Primary care electronic medication record discrepancies in patients starting treatment at a hospital-based ambulatory care pharmacy and impact on prevalence of potential drug-drug interactions.

OBJECTIVE: Our objective was to evaluate the prevalence of discrepancies between primary care electronic medication records (EMR) and patient reported medication (PRM) in ambulatory patients starting a hospital dispensing treatment (HDT) at a hospital-based ambulatory care pharmacy (HACPh). Our secondary aims were to analyse factors associated with the presence of discrepancies and their impact on the prevalence of potential drug-drug interactions (DDIs) with the HDT. METHODS: Retrospective study including 230 patients starting a HDT at the HACPh. Pharmacists interviewed patients and PRM was compared with EMR. Discrepancies were classified as omissions (medication in the PRM not present in the EMR) and commissions (medication active in the EMR that the patients were not taking). Potential DDIs with the HDT were screened, and univariate and multivariate analyses were performed to detect factors associated with the presence of discrepancies. RESULTS: We identified 221 discrepancies in 116 (50.4%) patients. Being visited by three or more medical specialties (OR 1.93, 95% CI 1.11 to 3.37) and attending private healthcare (OR 4.36, 95% CI 1.14 to 16.72) in the 12 months before the study inclusion were the factors independently associated with the presence of discrepancies. Among patients with commissions (n=91), 15.4% had a potential DDI between the HDT and one medication from the EMR that they were not taking at that moment. Among patients with omissions (n=45), 11.1% had a potential DDI between the HDT and a medication in the PRM not present in the EMR. CONCLUSIONS: About 40% of patients had one or more medications in the EMR which they were not taking and one fifth used medications that were not listed in the EMR. EMR should not be used as the only source of information when screening for DDIs, especially in patients followed by different medical specialties or combining private and public healthcare.

Suboptimal Concentrations of Ceftazidime/Avibactam (CAZ-AVI) May Select for CAZ-AVI Resistance in Extensively Drug-Resistant Pseudomonas aeruginosa: In Vivo and In Vitro Evidence.

This study correlates in vivo findings in a patient with an extensively drug-resistant (XDR) P. aeruginosa infection who developed resistance to ceftazidime-avibactam (CAZ-AVI) with in vitro results of a 7-day hollow-fiber infection model (HFIM) testing the same bacterial strain. The patient was critically ill with ventilator-associated pneumonia caused by XDR P. aeruginosa ST175 with CAZ-AVI MIC of 6 mg/L and was treated with CAZ-AVI in continuous infusion at doses adjusted for renal function. Plasma concentrations of CAZ-AVI were analyzed on days 3, 7, and 10. In the HIFM, the efficacy of different steady-state concentrations (Css) of CAZ-AVI (12, 18, 30 and 48 mg/L) was evaluated. In both models, a correlation was observed between the decreasing plasma levels of CAZ-AVI and the emergence of resistance. In the HIFM, a Css of 30 and 48 mg/L (corresponding to 5× and 8× MIC) had a bactericidal effect without selecting resistant mutants, whereas a Css of 12 and 18 mg/L (corresponding to 2× and 3× MIC) failed to prevent the emergence of resistance. CAZ/AVI resistance development was caused by the selection of a single ampC mutation in both patient and HFIM. Until further data are available, strategies to achieve plasma CAZ-AVI levels at least 4× MIC could be of interest, particularly in severe and high-inoculum infections caused by XDR P. aeruginosa with high CAZ-AVI MICs.

Therapeutic Drug Monitoring and Prolonged Infusions of Ceftolozane/Tazobactam for MDR/XDR Pseudomonas aeruginosa Infections: An Observational Study.

BACKGROUND AND OBJECTIVE: Prolonged infusion of ceftolozane/tazobactam (C/T) is a strategy used to increase achievement of pharmacokinetic/pharmacodynamic targets for the treatment of multi- or extensively drug-resistant MDR/XDR Gram-negative microorganisms. The objective of this study was to describe our therapeutic drug monitoring (TDM) experience of C/T administered by prolonged infusion or intermittent infusion to patients with MDR/XDR Pseudomonas aeruginosa infections. Our outcomes of interest were pharmacokinetic/pharmacodynamic target achievement and clinical cure. METHODS: Patients with MDR/XDR P. aeruginosa infections treated with C/T were enrolled between February 2018 and February 2020. Blood samples were obtained as part of a TDM program. The pharmacokinetic/pharmacodynamic therapeutic target of C/T was defined as 100% of the duration of the dosing interval that free concentrations are above the minimum inhibitory concentration (MIC) (100 %ƒT ≥ MIC) of the causative pathogen. Dose changes were performed according to TDM results. RESULTS: Forty patients were included: 13 (32.5%) with a proven MDR and 27 (67.5%) with a XDR P. aeruginosa infection. C/T was administered by prolonged infusion in 32 (80%) patients and by intermittent infusion in 8 (20%) patients. Lower doses were administered in the prolonged infusion compared to the intermittent infusion group [3 (9.4%) vs. 5 (62.5%] patients received a dose of 9 g/day (ceftolozane 2 g + tazobactam 1 g, every 8 h; p = 0.004). All patients achieved the pharmacokinetic/pharmacodynamic target and C/T concentrations exceeded 10 × MIC in > 50% of patients in both groups. TDM-recommended dose reductions occurred in 19 (47.5%) patients, being 16 (84.2%) in the prolonged infusion group. A high proportion of patients achieved clinical cure (82.5%). CONCLUSIONS: The administration of C/T by prolonged infusion with TDM-guided dosing allowed the achievement of a pharmacokinetic/pharmacodynamic target even at lower doses. C/T showed a high efficacy for treating MDR/XDR P. aeruginosa infections.

Comparison of Ceftolozane/Tazobactam Infusion Regimens in a Hollow-Fiber Infection Model against Extensively Drug-Resistant Pseudomonas aeruginosa Isolates.

The aim of this study was to compare the efficacy of intermittent (1-h), extended (4-h), and continuous ceftolozane-tazobactam (C/T) infusion against three extensively drug-resistant (XDR) sequence type (ST) 175 P. aeruginosa isolates with different susceptibilities to C/T (MIC = 2 to 16 mg/L) in a 7-day hollow-fiber infection model (HFIM). C/T in continuous infusion achieved the largest reduction in total number of bacterial colonies in the overall treatment arms for both C/T-susceptible and -resistant isolates. It was also the only regimen with bactericidal activity against all three isolates. These data suggest that continuous C/T infusion should be considered a potential treatment for infections caused by XDR P. aeruginosa isolates, including nonsusceptible ones. Proper use of C/T dosing regimens may lead to better clinical management of XDR P. aeruginosa infections. IMPORTANCE Ceftolozane-tazobactam (C/T) is an antipseudomonal antibiotic with a high clinical impact in treating infection caused by extensively drug-resistant (XDR) Pseudomonas aeruginosa isolates, but resistance is emerging. Given its time-dependent behavior, C/T continuous infusion can improve exposure and therefore the pharmacokinetic/pharmacodynamic target attainment. We compared the efficacy of intermittent, extended, and continuous C/T infusion against three XDR ST175 P. aeruginosa isolates with different C/T MICs by means of an in vitro dynamic hollow-fiber model. We demonstrated that C/T in continuous infusion achieved the largest reduction in bacterial density in the overall treatment arms for both susceptible and resistant isolates. It was also the only regimen with bactericidal activity against all three isolates. Through this study, we want to demonstrate that developing individually tailored antimicrobial treatments is becoming essential. Our results support the role of C/T level monitoring and of dose adjustments for better clinical management and outcomes.

Impact of the COVID-19 pandemic: Community and hospital shared pharmaceutical care model. Satisfaction and acceptability of patients with HIV infection on antiretroviral treatment / Impacto de la pandemia COVID-19: Modelo de atención farmacéutica compartida comunitaria y hospitalaria. Satisfacción y aceptabilidad depacientes con infección VIH en tratamiento antirretroviral

Background. The health crisis due to the COVID-19 pandemic is a challenge in the dispensing of outpatient hospital medication (OHM). Models of Antiretroviral Therapy (ART) based on community pharmacy support (ARTCP) have proven to be successful. The aim was to evaluate the degree of satisfaction, acceptability and limitations of the implementation of ARTCP, in the context of a pandemic, in our environment. Methods. Descriptive cross-sectional study carried out in a Barcelona hospital, during the months of July-November 2020. A telephone survey was carried out via a questionnaire on the quality dimensions of the model (degree of satisfaction, acceptability) and associated inconveniences. Data collected: demographics, antiretroviral treatment (ART), concomitant medication, drug interactions (DDIs), CD4 lymphocyte count and plasma viraemia. Data analysis included descriptive statistics. Results. A total of 533 (78.0%) HIV patients receiving ART were included. 71.9% (383/533) of these patients were very satisfied and 76.2% preferred attending the community pharmacy rather than the hospital. The mean satisfaction rating was 9.3 (DS: 1.4). The benefits reported were: 1) proximity to home (406: 76.1%); 2) lower risk of contagion of COVID-19 (318: 59.7%); 3) shorter waiting time (201: 37.1%); 4) time flexibility (104: 19.5%); 5) reduction of financial expenses (35: 6.57%). A total of 11 (2%) patients reported no benefit. Only 22.9% reported disadvantages associated with ARTCP: 1) lack of privacy (65: 12.2%); 2) lack of coordinationorganization (57: 10.7%). Conclusion. The COVID-19 pandemic has had an impact on the provision of pharmaceutical care for HIV patients. The ARTPC model has proved efficient, with patients reporting a high degree of satisfaction. (AU)

Introducción. La crisis sanitaria por la pandemia COVID-19 plantea un desafío en la dispensación de la medicación hospitalaria de dispensación ambulatoria (MHDA). Los modelos de terapia antirretroviral basados en el apoyo de la farmacia comunitaria (TARFC) han demostrado tener éxito. El objetivo del estudio fue evaluar el grado de satisfacción, aceptabilidad y limitaciones de la implementación del TARFC, en contexto de pandemia, en nuestro entorno. Métodos. Estudio descriptivo transversal realizado en un hospital de Barcelona, durante los meses de julio-noviembre del 2020. Se realizó una encuesta telefónica, mediante un cuestionario sobre dimensiones de calidad del modelo (grado de satisfacción, aceptabilidad) e inconvenientes asociados. Se recogieron datos: demográficos, tratamiento antirretroviral (TAR), medicación concomitante, interacciones farmacológicas (DDIs), recuento de linfocitos CD4 y viremia plasmática. El análisis de datos incluyó estadística descriptiva. Resultados. Se incluyeron 533 pacientes VIH adherentes al TAR. El 71,9% (383/533) de pacientes estaban muy satisfechos y el 76,2% preferían acudir a la farmacia comunitaria frente a la hospitalaria. La calificación de satisfacción media fue de 9,3 (DS: 1,4). Los beneficios reportados fueron: 1) cercanía al domicilio (406: 76,1%); 2) menor riesgo de contagio de COVID-19 (318: 59,7%) 3) menor tiempo de espera (201: 37,1%); 4) flexibilidad horaria (104: 19,5%); 5) reducción de gastos económicos (35: 6,57%). Un total de 11 (2%) pacientes no reportaron ningún beneficio. Únicamente el 22,9% reportaron desventajas asociadas al TARFC: 1) falta de privacidad (65:12,2%); 2) falta de coordinación-organización (57: 10,7%) Conclusión. La pandemia de COVID-19 tiene un impacto en la prestación de atención farmacéutica al VIH. El modelo TARFC ha resultado eficiente con un elevado grado de satisfacción por parte de los pacientes. (AU)

Impact of ceftolozane/tazobactam concentrations in continuous infusion against extensively drug-resistant Pseudomonas aeruginosa isolates in a hollow-fiber infection model.

Ceftolozane/tazobactam (C/T) has emerged as a potential agent for the treatment of extensively drug-resistant (XDR) Pseudomonas aeruginosa infections. As it is a time-dependent antimicrobial, prolonged infusion may help achieve pharmacokinetic/pharmacodynamic (PK/PD) targets. To compare alternative steady-state concentrations (Css) of C/T in continuous infusion (CI) against three XDR P. aeruginosa ST175 isolates with C/T minimum inhibitory concentration (MIC) values of 2 to 16 mg/L in a hollow-fiber infection model (HFIM). Duplicate 10-day HFIM assays were performed to evaluate Css of C/T in CI: one compared 20 and 45 mg/L against the C/T-susceptible isolate while the other compared 45 and 80 mg/L against the two C/T-non-susceptible isolates. C/T resistance emerged when C/T-susceptible isolate was treated with C/T in CI at a Css of 20 mg/L; which showed a deletion in the gene encoding AmpC ß-lactamase. The higher dosing regimen (80 mg/L) showed a slight advantage in effectiveness. The higher dosing regimen has the greatest bactericidal effect, regardless of C/T MIC. Exposure to the suboptimal Css of 20 mg/L led to the emergence of C/T resistance in the susceptible isolate. Antimicrobial regimens should be optimized through C/T levels monitoring and dose adjustments to improve clinical management.

Pharmacokinetics and Pharmacodynamics of Meropenem by Extended or Continuous Infusion in Low Body Weight Critically Ill Patients.

Background: Pathophysiological changes such as extreme body weights in critically ill patients with severe infections may alter the pharmacokinetics (PK) of antimicrobials, leading to treatment failure or toxicity. There are almost no PK data on meropenem in critically ill patients with low body weight (LwBW) and therefore information is lacking on the most appropriate dosing regimens, especially when administered by extended infusion. Objectives: To assess if the current administered doses of meropenem could lead to supratherapeutic concentrations in LwBW patients and to identify the factors independently associated with overexposure. Methods: A matched case-control 1:1 study of surgical critically ill patients treated with meropenem administered by extended or continuous infusion and undergoing therapeutic drug monitoring was conducted. Cases (patients with LwBW (body mass index (BMI) < 18.5 kg/m2)) were matched with normal body weight controls (NBW) (patients with BMI ≥ 18.5 kg/m2 and ≤30 kg/m2)) by age, gender, baseline renal function and severity status (APACHE II score). A 100% fT > MIC was considered an optimal pharmacokinetic/pharmacodynamic (PK/PD) target and 100% fT > 10 × MIC as supratherapeutic exposure. Results: Thirty-six patients (18 cases and 18 controls) were included (median (range) age, 57.5 (26-75) years; 20 (55.6% male)). Meropenem was administered by 6 h (extended) or 8 h (continuous) infusion at a median (range) daily dose of 5 (1-6) g/day. Similar median meropenem trough plasma concentrations (Cmin,ss), measured pre-dose on day three to four of treatment) were observed in the two groups (19.9 (22.2) mg/L vs 22.4 (25.8) mg/L, p > 0.999). No differences in the proportion of patients with an optimal or a supratherapeutic PKPD target between cases and controls were observed. A baseline estimated glomerular filtration rate (eGFR) < 90 mL/min was the only factor independently associated with a supratherapeutic PK/PD target. Conclusions: LwBW seems not to be a risk factor for achieving a supratherapeutic PK/PD target in critically ill patients receiving meropenem at standard doses by extended or continuous infusion.

Time-Kill Evaluation of Antibiotic Combinations Containing Ceftazidime-Avibactam against Extensively Drug-Resistant Pseudomonas aeruginosa and Their Potential Role against Ceftazidime-Avibactam-Resistant Isolates.

Ceftazidime-avibactam (CZA) has emerged as a promising solution to the lack of new antibiotics against Pseudomonas aeruginosa infections. Data from in vitro assays of CZA combinations, however, are scarce. The objective of our study was to perform a time-kill analysis of the effectiveness of CZA alone and in combination with other antibiotics against a collection of extensively drug-resistant (XDR) P. aeruginosa isolates. Twenty-one previously characterized representative XDR P. aeruginosa isolates were selected. Antibiotic susceptibility was tested by broth microdilution, and results were interpreted using CLSI criteria. The time-kill experiments were performed in duplicate for each isolate. Antibiotics were tested at clinically achievable free-drug concentrations. Different treatment options, including CZA alone and combined with amikacin, aztreonam, meropenem, and colistin, were evaluated to identify the most effective combinations. Seven isolates were resistant to CZA (MIC ≥ 16/4 mg/liter), including four metallo-ß-lactamase (MBL)-carrying isolates and two class A carbapenemases. Five of them were resistant or intermediate to aztreonam (MIC ≥ 16 mg/liter). Three isolates were resistant to amikacin (MIC ≥ 64 mg/liter) and one to colistin (MIC ≥ 4 mg/liter). CZA monotherapy had a bactericidal effect in 100% (14/14) of the CZA-susceptible isolates. Combination therapies achieved a greater overall reduction in bacterial load than monotherapy for the CZA-resistant isolates. CZA plus colistin was additive or synergistic in 100% (7/7) of the CZA-resistant isolates, while CZA plus amikacin and CZA plus aztreonam were additive or synergistic in 85%. CZA combined with colistin, amikacin, or aztreonam was more effective than monotherapy against XDR P. aeruginosa isolates. A CZA combination could be useful for treating XDR P. aeruginosa infections, including those caused by CZA-resistant isolates. IMPORTANCE The emergence of resistance to antibiotics is a serious public health problem worldwide and can be a cause of mortality. For this reason, antibiotic treatment is compromised, and we have few therapeutic options to treat infections. The main goal of our study is to search for new treatment options for infections caused by difficult-to-treat resistant germs. Pseudomonas aeruginosa is a Gram-negative bacterium distributed throughout the world with the ability to become resistant to most available antibiotics. Ceftazidime-avibactam (CZA) emerged as a promising solution to the lack of new antibiotics against infections caused by P. aeruginosa strains. This study intended to analyze the effect of CZA alone or in combination with other available antibiotics against P. aeruginosa strains. The combination of CZA with other antibiotics could be more effective than monotherapy against extensively drug-resistant P. aeruginosa strains.