Impact of Maximizing Css/MIC Ratio on Efficacy of Continuous Infusion Meropenem Against Documented Gram-Negative Infections in Critically Ill Patients and Population Pharmacokinetic/Pharmacodynamic Analysis to Support Treatment Optimization

Introduction: optimal treatment of Gram-negative infections in critically ill patients is challenged by changing pathophysiological conditions, reduced antimicrobial susceptibility and limited therapeutic options. The aim of this study was to assess the impact of maximizing Css/MIC ratio on efficacy of continuous infusion (CI) meropenem in treating documented Gram-negative infections in critically ill patients and to perform a population pharmacokinetic/pharmacodynamic analysis to support treatment optimization.Materials and Methods: Classification and regression tree (CART) analysis was used to identify whether a cutoff of steady-state meropenem concentration (Css)-to-minimum inhibitory concentration (MIC) (Css/MIC) ratio correlated with favorable clinical outcome. A non-parametric approach with Pmetrics was used for pharmacokinetic analysis and covariate evaluation. The probability of target attainment (PTA) of the identified Css/MIC ratio was calculated by means of Monte Carlo simulations. Cumulative fraction of response (CFRs) were calculated against common Enterobacterales, P. aeruginosa and A. baumannii as well.Results: a total of 74 patients with 183 meropenem Css were included. CART analysis identified a Css/MIC ratio ≥4.63 as cutoff value significantly associated with favorable clinical outcomes. Multivariate regression analysis confirmed the association [OR (95%CI): 20.440 (2.063–202.522); p < 0.01]. Creatinine clearance (CLCR) was the only covariate associated with meropenem clearance. Monte Carlo simulations showed that, across different classes of renal function, dosages of meropenem ranging between 0.5 and 2 g q6h over 6 h (namely by CI) may grant PTAs of Css/MIC ratios ≥4.63 against susceptible pathogens with an MIC up to the EUCAST clinical breakpoint of 2 mg/L. The CFRs achievable with these dosages were very high (>90%) against Enterobacterales across all the classes of renal function and against P. aeruginosa among patients with CLCR < 30 ml/min/1.73 m2, and quite lower against A. baumannii.Discussion: our findings suggest that Css/MIC ratio ≥4.63 may be considered the pharmacodynamic target useful at maximizing the efficacy of CI meropenem in the treatment of Gram-negative infections in critically ill patients. Dosages ranging between 0.5 g q6h and 2 g q6h by CI may maximize the probability of favorable clinical outcome against meropenem-susceptible Gram-negative pathogens among critically ill patients having different degrees of renal function.

Population Pharmacokinetics and Pharmacodynamic Target Attainment of Isavuconazole against Aspergillus fumigatus and Aspergillus flavus in Adult Patients with Invasive Fungal Diseases: Should Therapeutic Drug Monitoring for Isavuconazole Be Considered as Mandatory as for the Other Mold-Active Azoles?

Isavuconazole is a newer broad-spectrum triazole approved for the treatment of invasive fungal disease. The objective of this study was to conduct a population pharmacokinetic and pharmacodynamic analysis of isavuconazole in a retrospective cohort of hospitalized patients. A nonlinear mixed-effect approach with Monte Carlo simulations was conducted to assess the probability of target attainment (PTA) of an area under the concentration–time curve (AUC24 h)/minimum inhibitory concentration (MIC) ratio of 33.4 (defined as efficacy threshold against A. fumigatus and A. flavus) associated with a maintenance dose (MD) of 100, 200 and 300 mg daily after loading. The cumulative fraction of response (CFR) against the EUCAST MIC distributions of A. fumigatus and A. flavus was calculated as well. The proportion of trough concentrations (Ctrough) exceeding a defined threshold of toxicity (>5.13 mg/L) was estimated. A total of 50 patients, with a median age of 61.5 years, provided 199 plasma isavuconazole concentrations. Invasive pulmonary aspergillosis was the prevalent type of infection and accounted for 80% (40/50) of cases. No clinical covariates were retained by the model. With the standard MD of 200 mg daily, CFRs were always ≥90% during the first two months of treatment. The risk of Ctrough < 1.0 mg/L was around 1%, and that of Ctrough > 5.13 mg/L was 27.7 and 39.2% at 28 and 60 days, respectively, due to isavuconazole accumulation over time. Our findings suggest that TDM for isavuconazole should not be considered as mandatory as for the other mold-active azoles voriconazole and posaconazole.

Antithymocyte globulin exposure in CD34+ T-cell depleted allogeneic hematopoietic cell transplantation

Traditional weight-based dosing results in variable rabbit anti-thymocyte-globulin (rATG) clearance that can delay CD4+ T-cell immune reconstitution (CD4+IR) leading to higher mortality. In a retrospective, pharmacokinetic (PK)/pharmacodynamic analysis of patients undergoing their first CD34+ T-cell depleted (TCD) Allogeneic Hematopoietic Cell Transplantation (HCT) after myeloablative conditioning with rATG, we estimated post-HCT rATG exposure as area-under-the-curve (AUC;AU*d/L) using a validated population-PK model. We related rATG exposure to non-relapse mortality (NRM), CD4+IR (CD4+ ≥50/µL at 2 consecutive measures within 100 days after HCT), overall survival, relapse, and acute-graft versus host disease (GVHD) to define an optimal rATG-exposure. Cox-proportional hazard models, and multi-state competing risk models were used. 554 patients were included (age 0.1-73 years). Median post-HCT rATG exposure was 47AU*d/L (range 0-101). Low post-HCT AUC (&lt;30AU*d/L) was associated with lower risk of NRM (p&lt;0.01) and higher probability of achieving CD4+IR (p&lt;0.001). Patients who attained CD4+IR had a 7-fold lower 5-year NRM (p&lt;0.0001). Probability of achieving CD4+IR was 2.5-fold and 3-fold higher in the &lt;30AU*d/L-group, compared to 30-55AU*d/L and ≥55AU*d/L-groups, respectively. In multivariable analyses, post-HCT rATG-exposure ≥55AU*d/L was associated with an increased risk of NRM (HR 3.42,95%CI 1.26-9.30). In the malignancy subgroup (n=515) a 10-fold and 7-fold increased NRM, was observed in the &gt;55AU*d/L and 30-55AU*d/L groups, respectively, compared to &lt;30AU*d/L group. Post-HCT rATG exposure ≥55AU*d/L was associated with higher risk of acute GVHD (HR 2.28,95%CI 1.01-5.16). High post-HCT rATG-exposure is associated with higher NRM secondary to poor CD4+IR after TCD-HCT. Using personalized PK-directed rATG dosing to achieve optimal exposure may improve survival after HCT.