Guiding the starting dose of the once-daily formulation of tacrolimus in "de novo" adult renal transplant patients: a population approach.

Aims: The once-daily extended-release tacrolimus formulation (ER-Tac) has demonstrated similar efficacy and safety to the twice-daily immediate-release formulation (IR-Tac), but few population-based pharmacokinetic models have been developed in de novo kidney transplant patients to optimize doses. Therefore, this study aimed i) at developing a population pharmacokinetic model for ER-Tac in de novo adult kidney transplant patients ii) and identifying genetic factors and time-varying covariates predictive of pharmacokinetic variability to guide tacrolimus dosage during the early post-transplant period. Methods: A total of 1,067 blood tacrolimus concentrations from 138 kidney transplant patients were analyzed. A total of 29 out of 138 patients were intensively sampled for 24 h on the day 5 post-transplantation; meanwhile, for the remaining patients, concentrations were collected on days 5, 10, and 15 after transplantation. Tacrolimus daily doses and genetic and demographic characteristics were retrieved from the medical files. Biochemistry time-varying covariates were obtained on different days over the pharmacokinetic (PK) study. A simultaneous PK analysis of all concentrations was carried out using the non-linear mixed-effects approach with NONMEM 7.5. Results: A two-compartment model with linear elimination and delayed absorption best described the tacrolimus pharmacokinetics. Between-patient variability was associated with oral blood clearance (CL/F) and the central compartment distribution volume (Vc/F). Tacrolimus concentrations standardized to a hematocrit value of 45% significantly improved the model (p < 0.001). This method outperformed the standard covariate modeling of the hematocrit-blood clearance relationship. The effect of the CYP3A5 genotype was statistically (p < 0.001) and clinically significant on CL/F. The CL/F of patients who were CYP3A5*1 carriers was 51% higher than that of CYP3A5*1 non-carriers. Age also influenced CL/F variability (p < 0.001). Specifically, CL/F declined by 0.0562 units per each increased year from the value estimated in patients who were 60 years and younger. Conclusion: The 36% between-patient variability in CL/F was explained by CYP3A5 genotype, age, and hematocrit. Hematocrit standardization to 45% explained the variability of tacrolimus whole-blood concentrations, and this was of utmost importance in order to better interpret whole-blood tacrolimus concentrations during therapeutic drug monitoring. The dose requirements of CYP3A5*/1 carriers in patients aged 60 years or younger would be highest, while CYP3A5*/1 non-carriers older than 60 years would require the lowest doses.

Efficacy of extended infusion of ß-lactam antibiotics for the treatment of febrile neutropenia in haematologic patients (BEATLE): a randomised, multicentre, open-label, superiority clinical trial.

OBJECTIVES: The efficacy of extended infusions (EI) of ß-lactam antibiotics for optimising outcomes in febrile neutropenia is unclear. We assessed whether the administration of ß-lactams was more effective in EI than in intermittent infusion (II) for the treatment of febrile neutropenia. METHODS: We performed a randomised, open-label, superiority clinical trial of patients with febrile neutropenia at four Spanish university hospitals. Patients undergoing haematopoietic stem cell transplantation or with acute leukaemia receiving chemotherapy who required empirical antibiotic treatment for febrile neutropenia were randomly assigned (1:1) to receive EI of ß-lactam or II after a first dose in bolus. The choice of antipseudomonal ß-lactam was left to the discretion of the attending physician. The primary endpoint was treatment success at day 5, defined as defervescence without modifying the antibiotic treatment. Secondary endpoints included adverse events, attainment of the pharmacokinetic/pharmacodynamic target of 50, 75 and 100%ƒuT>MIC, and 30-day mortality. RESULTS: Between November 19, 2019 and June 22, 2022, 295 patients we screened for eligibility, of whom 150 were randomly assigned to receive EI (n=77) or II (n=73) of the antipseudomonal ß-lactam of choice. In the intention-to-treat analysis, treatment success at day 5 was achieved in 39/77 patients (50.6%) receiving EI versus 46/73 patients (63.0%) receiving II (risk difference -12.4%; 95% confidence interval, -29.4 to 4.7, p=0.17). The pharmacokinetic/pharmacodynamic targets of 75 and 100% ƒuT>MIC for empirical treatment were achieved more frequently in the EI group. No statistically-significant differences were found between groups in terms of adverse events or 30-day mortality. CONCLUSIONS: Our findings do not support the routine use of empirical EI of ß-lactams in febrile neutropenia. Further studies should consider the clinical heterogeneity of febrile neutropenia and focus on patients with sepsis/septic shock and microbiologically documented infections, particularly those with infections caused by microorganisms less susceptible to ß-lactams.

Efficacy and safety of colistin plus beta-lactams for bone and joint infection caused by fluoroquinolone-resistant gram-negative bacilli: a prospective multicenter study.

OBJECTIVES: The prognosis of bone and joint infections (BJI) caused by Gram-negative bacilli (GNB) worsens significantly in the face of fluoroquinolone-resistance. In this setting, scarce pre-clinical and clinical reports suggest that intravenous beta-lactams plus colistin may improve outcome. Our aim was to assess the efficacy and safety of this treatment in a well-characterized prospective cohort. METHODS: Observational, prospective, non-comparative, multicenter (14 hospitals) study of adults with BJI caused by fluoroquinolone-resistant GNB treated with surgery and intravenous beta-lactams plus colistin for ≥ 21 days. The primary endpoint was the cure rate. RESULTS: Of the 44 cases included (median age 72 years [IQR 50-81], 22 [50%] women), 32 (73%) had an orthopedic device-related infection, including 17 (39%) prosthetic joints. Enterobacterales were responsible for 27 (61%) episodes, and Pseudomonas spp for 17 (39%), with an overall rate of MDR/XDR GNB infections of 27/44 (61%). Patients were treated with colistin plus intravenous beta-lactam for 28 days (IQR 22-37), followed by intravenous beta-lactam alone for 19 days (IQR 5-35). The cure rate (intention-to-treat analysis; median follow-up = 24 months, IQR 19-30) was 82% (95% CI 68%-90%) and particularly, 80% (95% CI 55%-93%) among patients managed with implant retention. Adverse events (AEs) leading to antimicrobial withdrawal occurred in 10 (23%) cases, all of which were reversible. Colistin AEs were associated with higher plasma drug concentrations (2.8 mg/L vs. 0.9 mg/L, p = 0.0001). CONCLUSIONS: Combination therapy with intravenous beta-lactams plus colistin is an effective regimen for BJI caused by fluoroquinolone-resistant GNB. AEs were reversible and potentially preventable by close therapeutic drug monitoring.

Vedolizumab and ART in recent HIV-1 infection unveil the role of α4ß7 in reservoir size.

BACKGROUNDWe evaluated the safety and viral rebound, after analytical treatment interruption (ATI), of vedolizumab and ART in recent HIV-1 infection. We used this model to analyze the effect of α4ß7 on the HIV-1 reservoir size.METHODSParticipants started ART with monthly vedolizumab infusions, and ATI was performed at week 24. Biopsies were obtained from ileum and cecum at baseline and week 24. Vedolizumab levels, HIV-1 reservoir, flow cytometry, and cell-sorting and antibody competition experiments were assayed.RESULTSVedolizumab was safe and well tolerated. No participant achieved undetectable viremia off ART 24 weeks after ATI. Only a modest effect on the time to achieve more than 1,000 HIV-1 RNA copies/mL and the proportion of participants off ART was observed, being higher in the vedolizumab group compared with historical controls. Just before ATI, α4ß7 expression was associated with HIV-1 DNA and RNA in peripheral blood and with PD1 and TIGIT levels. Importantly, a complete blocking of α4ß7 was observed on peripheral CD4+ T cells but not in gut (ileum and cecum), where α4ß7 blockade and vedolizumab levels were inversely associated with HIV-1 DNA.CONCLUSIONOur findings support α4ß7 as an important determinant in HIV-1 reservoir size, suggesting the complete α4ß7 blockade in tissue as a promising tool for HIV-cure combination strategies.TRIAL REGISTRATIONClinicalTrials.gov NCT03577782.FUNDINGThis work was supported by the Instituto de Salud Carlos III (Fondo Europeo de Desarrollo Regional, "a way to make Europe," research contracts FI17/00186 and FI19/00083 and research projects PI18/01532, PI19/01127, PI22/01796), Conserjería de Economía, Conocimiento, Empresas y Universidad, Junta de Andalucía (research projects P20/00906), the Red Temática de Investigación Cooperativa en SIDA (RD16/0025/0020), and the Spanish National Research Council.

Calculation of reference intervals for the concentrations of α-tocopherol and retinol in serum using indirect data-mining procedures.

BACKGROUND: Establishing adequate reference intervals (RIs) for vitamins A and E is essential for diagnosing and preventing deficiencies. Due to the current boom in data mining and its easy applicability, more laboratories are establishing RIs using indirect methods. Our study aims to obtain RIs using four indirect data-mining procedures (Bhattacharya, Hoffmann, Kosmic, and RefineR) for vitamins A and E. MATERIAL AND METHODS: 8943 individuals were collected to establish the RIs. After using different data cleaning steps and checking whether these data should be divided according to age and gender based on multiple linear regression and variance component analyses, indirect RIs were calculated using specific Excel spreadsheets or R-packages software. RESULTS: A total of 2004 records were eligible. For vitamin A, the RIs obtained were (1.11 - 2.68) µmol/L, (1.13 - 2.70) µmol/L, (1.13 - 2.71) µmol/L, and (1.17 - 2.66) µmol/L using the Bhattacharya, Hoffmann, Kosmic and RefineR approaches, respectively. For vitamin E, these intervals were (17.3 - 49.9) µmol/L (Bhattacharya), (17.3 - 48.9) µmol/L (Hoffmann), (19.6 - 50.3) µmol/L (Kosmic), and (19.4 - 50.9) µmol/L (RefineR). In all cases, the RIs were comparable. CONCLUSIONS: Suitable RIs for vitamins A and E were calculated using four indirect methods that are suitable and adapted to our population's demographic characteristics.

Determination of ertapenem in plasma and ascitic fluid by UHPLC-MS/MS in cirrhotic patients with spontaneous bacterial peritonitis.

Objectives: Spontaneous bacterial peritonitis is a frequent severe complication in cirrhotic patients with ascites. Carbapenem antibiotics are currently the treatment of choice for patients with hospital-acquired or healthcare-related infections. However, there is limited evidence available on the efficacy of ertapenem in cirrhotic patients with spontaneous bacterial peritonitis. As a result, the pharmacokynetics and pharmacodynamics of this antibiotic are still unknown. The objective of this study was to develop and validate measurement procedures based on liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) to determine ertapenem concentrations in plasma and ascitic fluid. Methods: Samples were pretreated by acetronile protein-precipitation. Chromatographic separation is performed on a C18 reversed-phase Acquity®-UPLC®-BEHTM column (2.1 × 100 mm id, 1.7 µm) using a non-linear gradient of water/acetonitrile containing 0.1 % of formic acid at a flow rate of 0.4 mL/min. Ertapenem and its internal standard (ertapenem-D4) are detected by tandem mass spectrometry using positive electrospray ionization and multiple reaction monitoring, and using 476.2 â†’ 346.0/432.2 as mass transition for ertapenem and 480.2 â†’ 350.0 for its internal standard. Results: No significant interferences or carry-over contamination were observed. Imprecisions, absolute relative bias, matrix effects and normalized recoveries were ≤14.5 %, ≤9.3 % (92.8-104.5) % and (98.8-105.8) %, respectively. Chromatographic measurement procedures were linear from (0.50-100) mg/L. Conclusions: The measurement procedures based on UHPLC-MS/MS developed and validated in this study could be useful in pharmacokynetic and pharmacodynamic studies in subjects with liver cirrhosis who develop spontaneous bacterial peritonitis treated with ertapenem.

Comparative Efficacy of Continuous Ceftazidime Infusion vs. Intermittent Bolus against In Vitro Ceftazidime-Susceptible and -Resistant Pseudomonas aeruginosa Biofilm.

Background: As the anti-biofilm pharmacokinetic/pharmacodynamic (PK/PD) properties of antibiotics are not well-defined, we have evaluated the PK/PD indices for different regimens of ceftazidime (CAZ; with/without colistin) against Pseudomonas aeruginosa biofilm. Methods: We have used the Center for Disease Control and Prevention Biofilm Reactor with two susceptible (PAO1 and HUB-PAS) and one resistant (HUB-XDR) strains of P. aeruginosa. The regimens were CAZ monotherapies (mimicking a human dose of 2 g/8 h, CAZ-IB; 6 g/daily as continuous infusion at 50 mg/L, CAZ-CI50; and 9 g/daily at 70 mg/L, CAZ-CI70) and CAZ-colistin combinations. Efficacy was correlated with the CAZ PK/PD parameters. Results: CAZ-CI70 was the most effective monotherapy against CAZ-susceptible strains (Δlog CFU/mL 54-0 h = -4.15 ± 0.59 and -3.05 ± 0.5 for HUB-PAS and PAO1, respectively; p ≤ 0.007 vs. other monotherapies), and adding colistin improved the efficacy over CAZ monotherapy. CAZ monotherapies were ineffective against the HUB-XDR strain, and CAZ-CI50 plus colistin achieved higher efficacy than CAZ-IB with colistin. The PK/PD index that correlated best with anti-biofilm efficacy was fAUC0-24h/MIC (r2 = 0.78). Conclusions: CAZ exhibited dose-dependent anti-biofilm killing against P. aeruginosa, which was better explained by the fAUC0-24h/MIC index. CAZ-CI provided benefits compared to CAZ-IB, particularly when using higher doses and together with colistin. CAZ monotherapies were ineffective against the CAZ-resistant strain, independently of the optimized strategy and only CAZ-CI plus colistin appeared useful for clinical practice.

Measurement uncertainty estimation of free drug concentrations in clinical laboratories using equilibrium dialysis.

OBJECTIVES: Developing procedures based on equilibrium dialysis (ED) that allow measuring the free drug concentration in plasma improves therapeutic drug monitoring (TDM) in those cases where its measurement is justified. However, this procedure requires specific sample preparation and presents different pitfalls, which are not error-free. As with any result provided by a clinical laboratory, this one should be as accurate as possible to allow a correct clinical interpretation. The measurement uncertainty (MU) is a parameter that enables the accuracy of results to be known, and that is mandated by ISO 15189. Herein, this study suggests how the MU for the results of the free drug concentrations in serum could be estimated when an ED is used. METHODS: A combination of the top-down and bottom-up approaches was used to estimate the MU based on the ISO/TS 20914:2019 and JCGM 100:2008 guidelines, including the concentration of free phenytoin in serum, as an example. Different scenarios were incorporated considering or not a significant bias related to the primary drawbacks of ED: the non-specific binding, the volume shift effect and the Gibbs-Donnan effect. RESULTS: The expanded uncertainties estimated ranged between 13.0 and 30.9 %. The highest MU corresponded to the free drug concentrations in serum results when significant biases related to the volume shift and Gibbs-Donnan effects exist. CONCLUSIONS: A detailed estimation of MU for free drug concentrations is presented using ED, considering different scenarios. This study could stimulate clinical laboratories to perform MU studies and its application in TDM.

Development and validation of equilibrium dialysis UHPLC-MS/MS measurement procedures for total and unbound concentrations of bictegravir, dolutegravir, darunavir and doravirine in human plasma. Application to patients with HIV.

BACKGROUND: Fixed-dose combinations of antiretroviral drugs are commonly used to treat HIV infection and therapeutic monitoring is not part of routine clinical practice. However, drug concentrations monitoring might have role in different clinical scenarios as well as for research purposes. This study aimed to develop and validate UHPLC-MS/MS procedures for measuring total and unbound concentrations of bictegravir, dolutegravir, darunavir and doravirine in human plasma. MATERIAL AND METHODS: Equilibrium dialysis preceded sample preparation (based on protein precipitation) for measuring unbound antiretroviral concentrations. Chromatographic separations were achieved on an Acquity®-UPLC® HSS™-T3 column (50 mm × 2.1 mm; 1.8 µm) using a non-linear water/acetonitrile gradient containing 0.1 % formic acid at a 0.5 mL/min flow rate. Antiretrovirals were detected by tandem mass spectrometry in positive electrospray ionisation and multiple reaction monitoring modes. RESULTS: No significant interferences or carry-over were observed. Imprecisions, absolute relative biases, normalised matrix effects and recoveries were ≤15.0 %, ≤11.1 %, (94.7-104.1)% and (96.7-105.5)%, respectively. Non-linear measuring intervals were observed between (25-10,000) µg/L for total/plasma dialysate concentrations and linearity schemes (1.00-100) µg/L for buffer dialysate concentrations. CONCLUSIONS: The UHPLC-MS/MS procedures developed could be used for research purposes and therapeutic drug monitoring of antiretrovirals in routine clinical practice.

CYP3A5*3 and CYP3A4*22 Cluster Polymorphism Effects on LCP-Tac Tacrolimus Exposure: Population Pharmacokinetic Approach.

The aim of the study is to develop a population pharmacokinetic (PopPK) model and to investigate the influence of CYP3A5/CYP3A4 and ABCB1 single nucleotide polymorphisms (SNPs) on the Tacrolimus PK parameters after LCP-Tac formulation in stable adult renal transplant patients. The model was developed, using NONMEM v7.5, from full PK profiles from a clinical study (n = 30) and trough concentrations (C0) from patient follow-up (n = 68). The PK profile of the LCP-Tac formulation was best described by a two-compartment model with linear elimination, parameterized in elimination (CL/F) and distributional (CLD/F) clearances and central compartment (Vc/F) and peripheral compartment (Vp/F) distribution volumes. A time-lagged first-order absorption process was characterized using transit compartment models. According to the structural part of the base model, the LCP-Tac showed an absorption profile characterized by two transit compartments and a mean transit time of 3.02 h. Inter-individual variability was associated with CL/F, Vc/F, and Vp/F. Adding inter-occasion variability (IOV) on CL/F caused a statistically significant reduction in the model minimum objective function MOFV (p < 0.001). Genetic polymorphism of CYP3A5 and a cluster of CYP3A4/A5 SNPs statistically significantly influenced Tac CL/F. In conclusion, a PopPK model was successfully developed for LCP-Tac formulation in stable renal transplant patients. CYP3A4/A5 SNPs as a combined cluster including three different phenotypes (high, intermediate, and poor metabolizers) was the most powerful covariate to describe part of the inter-individual variability associated with apparent elimination clearance. Considering this covariate in the initial dose estimation and during the therapeutic drug monitoring (TDM) would probably optimize Tac exposure attainments.

Measurement of apixaban concentrations in different human biological fluids by UHPLC-MS/MS. Clinical pharmacokinetic application in a subject with chronic kidney disease and nonvalvular atrial fibrillation on haemodialysis.

BACKGROUND: Apixaban's technical sheet does not recommend its use in clinical practice for patients with chronic kidney disease undergoing haemodialysis. However, recent studies indicate that apixaban could be a safe oral anticoagulant in these kinds of patients who do not present valvular atrial fibrillation. We developed and validated ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) procedures for measuring apixaban concentrations in plasma, dialysate liquid, and urine. MATERIAL AND METHODS: Simple protein precipitation was implemented to prepare samples. Chromatographic separations were achieved on an Acquity®-UPLC®-BEHTM (2.1x100 mm id, 1.7 µm) reverse-phase C18 column using a water/acetonitrile non-linear gradient containing 0.1 % formic acid at a 0.4 mL/min flow rate. Apixaban and its internal standard (apixaban-d3) were detected by electrospray ionisation mass spectrometry in positive and multiple reaction monitoring modes, using transitions of 460.3 â†’ 199.0/443.2 and 463.3 â†’ 202.0, respectively. RESULTS: No significant interferences and carry-overs were observed. Precisions, absolute relative biases, normalised-matrix factors, and normalised recoveries were ≤ 12.2%, ≤8.0%, 94.3-105.1%, and 93.9-105.4%, respectively. Linearity was observed between 5 and 500 µg/L for plasma/dialysate liquid and 5-1000 µg/L for urine. CONCLUSIONS: The validated UHPLC-MS/MS procedures could help support a pharmacokinetic study in non-valvular atrial fibrillation subjects with chronic kidney disease undergoing haemodialysis and apixaban-based anticoagulant therapy.

Voriconazole Pharmacokinetics in Critically Ill Patients and Extracorporeal Membrane Oxygenation Support: A Retrospective Comparative Case-Control Study.

Voriconazole, an antifungal agent, displays high intra- and inter-individual variability. The predictive pharmacokinetic (PK) index requires a minimum plasma concentration (Cmin) in patient serum of between 1-5.5 mg/L. It is common to encounter fungal infections in patients undergoing extracorporeal membrane oxygenation (ECMO) support, and data regarding voriconazole PK changes during ECMO are scarce. Our study compared voriconazole PKs in patients with and without ECMO support in a retrospective cohort of critically-ill patients. Fifteen patients with 26 voriconazole Cmin determinations in the non-ECMO group and nine patients with 27 voriconazole Cmin determinations in the ECMO group were recruited. The ECMO group had lower Cmin (0.38 ± 2.98 vs. 3.62 ± 3.88, p < 0.001) and higher infratherapeutic Cmin values (16 vs. 1, p < 0.001) than the non-ECMO group. Multivariate analysis identified ECMO support (-0.668, CI95 -0.978--0.358) and plasma albumin levels (-0.023, CI95 -0.046--0.001) as risk factors for low Cmin values. When comparing pre- and post-therapeutic drug optimisation samples from the ECMO group, the dose required to achieve therapeutic Cmin was 6.44 mg/kg twice a day. Therapeutic drug optimisation is essential to improve target attainment.

A prospective controlled, randomized clinical trial of kidney transplant recipients developed personalized tacrolimus dosing using model-based Bayesian Prediction.

For three decades, tacrolimus (Tac) dose adjustment in clinical practice has been calculated empirically according to the manufacturer's labeling based on a patient's body weight. Here, we developed and validated a Population pharmacokinetic (PPK) model including pharmacogenetics (cluster CYP3A4/CYP3A5), age, and hematocrit. Our study aimed to assess the clinical applicability of this PPK model in the achievement of Tac Co (therapeutic trough Tac concentration) compared to the manufacturer's labelling dosage. A prospective two-arm, randomized, clinical trial was conducted to determine Tac starting and subsequent dose adjustments in 90 kidney transplant recipients. Patients were randomized to a control group with Tac adjustment according to the manufacturer's labeling or the PPK group adjusted to reach target Co (6-10 ng/ml) after the first steady state (primary endpoint) using a Bayesian prediction model (NONMEM). A significantly higher percentage of patients from the PPK group (54.8%) compared with the control group (20.8%) achieved the therapeutic target fulfilling 30% of the established superiority margin defined. Patients receiving PPK showed significantly less intra-patient variability compared to the control group, reached the Tac Co target sooner (5 days vs 10 days), and required significantly fewer Tac dose modifications compared to the control group within 90 days following kidney transplant. No statistically significant differences occurred in clinical outcomes. Thus, PPK-based Tac dosing offers significant superiority for starting Tac prescription over classical labeling-based dosing according to the body weight, which may optimize Tac-based therapy in the first days following transplantation.

First reported double drug-drug interaction in a cancer renal patient under everolimus treatment: therapeutic drug monitoring and review of literature.

Everolimus is an inhibitor of mammalian target of rapamycin (mTOR) used in both transplantation and cancer treatment (breast, renal and neuroendocrine). In transplantation, therapeutic drug monitoring (TDM) is recommended due to the potential drug-drug interactions with chronic medications, which can affect everolimus pharmacokinetics. In cancer treatment, everolimus is used at higher doses than in transplantation and without a systematic drug monitoring.We present a case report of a 72-year-old woman with epilepsy history to whom everolimus 10 mg QD was prescribed as third line of treatment for renal cell carcinoma (RCC). The potential drug interactions between everolimus and the patient's chronic medications, carbamazepine and phenytoin, are significant as both are known as strong inducers CYP3A4 metabolism, potentially leading to underexposure to everolimus.TDM of everolimus was recommended by the pharmacist. The literature suggests that a minimum plasma concentration (Cminss) of everolimus over 10 ng/ml is associated with better response to treatment and progression-free survival (PFS). The patient's everolimus dose had to be increased until 10 mg BID, and regular monitoring of everolimus levels showed an increase in Cminss from 3.7 ng/ml to 10.8 ng/ml.This case highlights the importance of checking for potential drug interactions and monitoring everolimus levels in patients on chronic medication, especially those with several inducers or inhibitors of CYP3A4 metabolism. TDM can help to ensure that patients are treated with their optimal dose, which can improve the effectiveness of the treatment or minimize the risk of toxicities.

Efficacy of meropenem extended infusion vs intermittent bolus monotherapy and in combination with colistin against Pseudomonas aeruginosa biofilm.

INTRODUCTION: Device-related infections are difficult to treat due to biofilms. In this setting, optimizing antibiotic efficacy is difficult as most pharmacokinetic/pharmacdynamic (PK/PD) studies have been performed on planktonic cells, and therapies are limited when multi-drug-resistant bacteria are involved. This study aimed to analyse the PK/PD indices of meropenem predicting anti-biofilm efficacy against meropenem-susceptible and meropenem-resistant strains of Pseudomonas aeruginosa. MATERIALS AND METHODS: Pharmacodynamics of meropenem dosages mimicking those of clinical practice (intermittent bolus of 2 g every 8 h; extended infusion of 2 g over 4 h every 8 h), with and without colistin, were evaluated with the CDC Biofilm Reactor in-vitro model for susceptible (PAO1) and extensively-drug-resistant (XDR-HUB3) P. aeruginosa. Efficacy was correlated with the PK/PD indices for meropenem. RESULTS: For PAO1, both meropenem regimens were bactericidal, with higher killing for extended infusion [∆log10 colony-forming units (CFU)/mL 54-0h=-4.66±0.93 for extended infusion vs ∆log10 CFU/mL 54-0h=-3.4±0.41 for intermittent bolus; P<0.001]. For XDR-HUB3, the intermittent bolus regimen was non-active, but extended infusion showed bactericidal effect (∆log10 CFU/mL 54-0h=-3.65±0.29; P<0.001). Time above minimum inhibitory concentration (f%T>MIC) had the best correlation with efficacy for both strains. The addition of colistin always improved meropenem activity, and resistant strains did not emerge. CONCLUSION: f%T>MIC was the PK/PD index that best correlated with the anti-biofilm efficacy of meropenem; it was better optimized when using the extended infusion regimen, allowing recovery of bactericidal activity in monotherapy, including activity against meropenem-resistant P. aeruginosa. Combining meropenem by extended infusion with colistin offered the most effective therapy for both strains. Optimizing meropenem dosing by extended infusion should be encouraged when treating biofilm-related infections.

The Effect of Intracellular Tacrolimus Exposure on Calcineurin Inhibition in Immediate- and Extended-Release Tacrolimus Formulations.

Despite intensive monitoring of whole blood tacrolimus concentrations, acute rejection after kidney transplantation occurs during tacrolimus therapy. Intracellular tacrolimus concentrations could better reflect exposure at the site of action and its pharmacodynamics (PD). Intracellular pharmacokinetic (PK) profile following different tacrolimus formulations (immediate-release (TAC-IR) and extended-release (TAC-LCP)) remains unclear. Therefore, the aim was to study intracellular tacrolimus PK of TAC-IR and TAC-LCP and its correlation with whole blood (WhB) PK and PD. A post-hoc analysis of a prospective, open-label, crossover investigator-driven clinical trial (NCT02961608) was performed. Intracellular and WhB tacrolimus 24 h time-concentration curves were measured in 23 stable kidney transplant recipients. PD analysis was evaluated measuring calcineurin activity (CNA) and simultaneous intracellular PK/PD modelling analysis was conducted. Higher dose-adjusted pre-dose intracellular concentrations (C0 and C24) and total exposure (AUC0-24) values were found for TAC-LCP than TAC-IR. Lower intracellular peak concentration (Cmax) was found after TAC-LCP. Correlations between C0, C24 and AUC0-24 were observed within both formulations. Intracellular kinetics seems to be limited by WhB disposition, in turn, limited by tacrolimus release/absorption processes from both formulations. The faster intracellular elimination after TAC-IR was translated into a more rapid recovery of CNA. An Emax model relating % inhibition and intracellular concentrations, including both formulations, showed an IC50, a concentration to achieve 50% CNA inhibition, of 43.9 pg/million cells.

Predictive Factors of Piperacillin Exposure and the Impact on Target Attainment after Continuous Infusion Administration to Critically Ill Patients.

Critically ill patients undergo significant pathophysiological changes that affect antibiotic pharmacokinetics. Piperacillin/tazobactam administered by continuous infusion (CI) improves pharmacokinetic/pharmacodynamic (PK/PD) target attainment. This study aimed to characterize piperacillin PK after CI administration of piperacillin/tazobactam in critically ill adult patients with preserved renal function and to determine the empirical optimal dosing regimen. A total of 218 piperacillin concentrations from 106 patients were simultaneously analyzed through the population PK approach. A two-compartment linear model best described the data. Creatinine clearance (CLCR) estimated by CKD-EPI was the covariate, the most predictive factor of piperacillin clearance (CL) interindividual variability. The mean (relative standard error) parameter estimates for the final model were: CL: 12.0 L/h (6.03%); central and peripheral compartment distribution volumes: 20.7 L (8.94%) and 62.4 L (50.80%), respectively; intercompartmental clearance: 4.8 L/h (26.4%). For the PK/PD target of 100% fT>1×MIC, 12 g of piperacillin provide a probability of target attainment > 90% for MIC < 16 mg/L, regardless of CLCR, but higher doses are needed for MIC = 16 mg/L when CLCR > 100 mL/min. For 100% fT>4×MIC, the highest dose (24 g/24 h) was not sufficient to ensure adequate exposure, except for MICs of 1 and 4 mg/L. Our model can be used as a support tool for initial dose guidance and during therapeutic drug monitoring.