Massimo Tempestilli

Background: Invasive fungal infections are associated with high morbidity and mortality, particularly among immunocompromised and critically ill patients. Antifungal therapy is complicated by substantial pharmacokinetic variability, drug–drug interactions, and narrow therapeutic windows for some agents. Although therapeutic drug monitoring (TDM) can optimize drug exposure, therapeutic targets vary across studies and guidelines. The aim of this review was to provide an updated overview of antifungal TDM and support the harmonization of therapeutic ranges based on pharmacokinetic/pharmacodynamic (PK/PD) evidence. Methods: A comprehensive search of major literature databases and international guidelines was conducted through November 2025 to identify studies reporting antifungal therapeutic targets and clinical applications of TDM. When therapeutic ranges differed across studies or guidelines, alternative targets were reported, considering the clinical settings and populations in which they were proposed. Results: Robust evidence supports routine TDM for triazoles with high pharmacokinetic variability, particularly voriconazole and posaconazole, for which target trough concentrations are well established and associated with clinical outcomes. For isavuconazole, routine TDM is not universally recommended but may benefit selected high-risk populations, including critically ill, pediatric, and obese patients and those receiving extracorporeal therapies. Conversely, routine TDM is not currently recommended for echinocandins or amphotericin B because of limited exposure–response data, although emerging evidence suggests that TDM may be useful in selected clinical scenarios. Variability in PK/PD targets, analytical methods, and preanalytical factors contributes to inconsistent implementation in clinical practice. Conclusions: Harmonization of antifungal therapeutic ranges is essential to improve the clinical utility of TDM and support individualized antifungal therapy. Further studies are required to establish standardized targets for all antifungal classes.

Remdesivir is the first antiviral drug against SARS-CoV-2 approved for use in COVID-19 patients. To study the pharmacokinetic inter-individual variability of remdesivir and its main metabolite GS-441524 in a real-world setting of COVID-19 inpatients and to identify possible associations with different demographic/biochemical variables. Inpatients affected by SARS-CoV-2 infections, undergoing standard-dose remdesivir treatment, were prospectively enrolled. Blood samples were collected on day 4, immediately after (C₀) and at 1 h (C₁) and 24 h (C₂₄) after infusion. Remdesivir and GS-441524 concentrations were measured using a validated UHPLC-MS/MS method and the AUC_0–24 was calculated. At baseline, COVID-19 severity (ICU or no ICU), sex, age, BMI and renal and liver functions were assessed. Transaminases and estimated glomerular filtration rate (e-GFR) were also evaluated during treatment. Linear regression, logistic regression and multiple linear regression tests were used for statistical comparisons of pharmacokinetic parameters and variables. Eighty-five patients were included. The mean (CV%) values of remdesivir were: C₀ 2091 (99.1%) ng/mL, C₁ 139.7 (272.4%) ng/mL and AUC_0–24 2791 (175.7%) ng·h/mL. The mean (CV%) values of GS-441524 were: C₀ 90.2 (49.5%) ng/mL, C₁ 104.9 (46.6%) ng/mL, C₂₄ 58.4 (66.9) ng/mL and AUC_0–24 1976 (52.6%) ng·h/mL. The multiple regression analysis showed that age (P < 0.05) and e-GFR (P < 0.01) were independent predictors of GS-441524 plasma exposure. Our results showed a high interpatient variability of remdesivir and GS-441524 likely due to both age and renal function in COVID-19 inpatients. Further research is required to understand whether the pharmacokinetics of remdesivir and its metabolites may influence drug-related efficacy or toxic effect.

To date, vitamin D seems to have a significant role in affecting the prevention and immunomodulation in COVID-19 disease. Nevertheless, it is important to highlight that this pro-hormone has other several activities, such as affecting drug concentrations, since it regulates the expression of cytochrome P450 (CYP) genes. Efavirenz (EFV) pharmacokinetics is influenced by CYPs, but no data are available in the literature concerning the association among vitamin D levels, seasonality (which affects vitamin D concentrations) and EFV plasma levels. For this reason, the aim of this study was to evaluate the effect of 25-hydroxy vitamin D (25(OH)D3) levels on EFV plasma concentrations in different seasons. We quantified 25(OH)D3 by using chemiluminescence immunoassay, whereas EFV plasma concentrations were quantified with the HPLC–PDA method. A total of 316 patients were enrolled in Turin and Rome. Overall, 25(OH)D3levels resulted in being inversely correlated with EFV concentrations. Some patients with EFV levels higher than 4000 ng/mL showed a deficient 25(OH)D3 concentration in Turin and Rome cohorts and together. EFV concentrations were different in patients without vitamin D supplementation, whereas, for vitamin D-administered individuals, no difference in EFV exposure was present. Concerning seasonality, EFV concentrations were associated with 25(OH)D3 deficiency only in winter and in spring, whereas a significant influence was highlighted for 25(OH)D3 stratification for deficient, insufficient and sufficient values in winter, spring and summer. A strong and inverse association between 25(OH)D3and EFV plasma concentrations was suggested. These data suggest that vitamin D is able to affect drug exposure in different seasons; thus, the achievement of the clinical outcome could be improved by also considering this pro-hormone.

Background Sofosbuvir plus daclatasvir achieves high rates of sustained virologic response (SVR), with no differences according to HIV serostatus. However, only limited information is available on the pharmacokinetic variability of sofosbuvir and daclatasvir in HIV/HCV-coinfected patients. Objectives The aim of this study was to identify patient-, treatment-, and disease-related factors that are significantly associated with sofosbuvir and daclatasvir plasma trough concentrations (C_trough), including liver and renal function, among HIV/HCV-coinfected persons. Methods In this observational cohort pilot study, HIV/HCV-coinfected patients undergoing sofosbuvir plus daclatasvir treatment were prospectively enrolled. Biochemical and viro-immunological parameters were assessed at baseline, week 4 (W4), end of treatment (EOT), and after EOT. The FIB-4 score and CKD-EPI equation were used to estimate liver disease and glomerular filtration rate (eGFR), respectively. For sofosbuvir, sofosbuvir metabolite (GS-331007), and daclatasvir, C_trough was measured at W4 and week 8 (W8), and the mean of the values at those two time points (mean-C_trough) was calculated. The Mann–Whitney test and Spearman’s rank correlation were used to evaluate the correlations between the mean-C_trough of each direct-acting antiviral (DAA) and the considered variables. Results Thirty-five patients were included (SVR 94%). An increased GS-331007 mean-C_trough was significantly correlated with a decreased eGFR at W4 (rho = −0.36; p = 0.037) and EOT (rho = −0.34; p = 0.048). There was a significant correlation between daclatasvir mean-C_trough and FIB-4 at all time points: baseline (rho = −0.35; p = 0.037), W4 (rho = −0.44; p = 0.008), EOT (rho = −0.40; p = 0.023), and after EOT (rho = −0.39; p = 0.028). Conclusions In HIV/HCV-coinfected patients in a real-world setting, exposure to a high GS-331007 C_trough was associated with a slight decrease in renal function, while advanced hepatic impairment was significantly associated with a lower daclatasvir C_trough. Though the clinical and therapeutic relevance of these findings may be limited, increasing clinicians’ knowledge regarding DAA exposure in difficult-to-treat patients could be relevant in single cases, and further investigations are warranted.

Due to potential changes in absorption, the pharmacokinetics (PK) of antiretroviral (ARV) drugs following gastrectomy should be monitored in people living with HIV. Actually, there is limited information on the PK profiles of ARV drugs in gastrectomized patients with HIV and for the most current regimens, including bictegravir, an integrase strand transfer inhibitor co-formulated with the NRTIs emtricitabine and tenofovir alafenamide in a single-tablet regimen for the once-daily treatment of HIV-1 infection in adults (BIC/FTC/TAF), ¹ PK data are lacking. ^{2, 3}

The immunological mechanisms underlying the clinical presentation of SARS-CoV-2 infection and those influencing the disease outcome remain to be defined. Myeloid-derived suppressor cells (MDSC) have been described to be highly increased during COVID-19, however, their role remains elusive. We performed an in depth analysis of MDSC in 128 SARS-CoV-2 infected patients. Polymorphonuclear (PMN)-MDSC expanded during COVID-19, in particular in patients who required intensive care treatments, and correlated with IL-1β, IL-6, IL-8, and TNF-α plasma levels. PMN-MDSC inhibited T-cells IFN-γ production upon SARS-CoV-2 peptides stimulation, through TGF-β- and iNOS-mediated mechanisms, possibly contrasting virus elimination. Accordingly, a multivariate regression analysis found a strong association between PMN-MDSC percentage and fatal outcome of the disease. The PMN-MDSC frequency was higher in non-survivors than survivors at the admission time, followed by a decreasing trend. Interestingly, this trend was associated with IL-6 increase in non-survivors but not in survivors. In conclusion, this study indicates PMN-MDSC as a novel factor in the pathogenesis of SARS-CoV2 infection, and open up to new therapeutic options.

Background: Remdesivir is a prodrug of the nucleoside analogue GS-441524 and is under evaluation for treatment of SARS-CoV-2-infected patients. Objectives: To evaluate the pharmacokinetics of remdesivir and GS-441524 in plasma, bronchoalveolar aspirate (BAS) and CSF in two critically ill COVID-19 patients. Methods: Remdesivir was administered at 200 mg loading dose on the first day followed by 12 days of 100 mg in two critically ill patients. Blood samples were collected immediately after (C0) and at 1 (C1) and 24 h (C24) after intravenous administration on day 3 until day 9. BAS samples were collected on Days 4, 7 and 9 from both patients while one CSF on Day 7 was obtained in one patient. Remdesivir and GS-441524 concentrations were measured in these samples using a validated UHPLC-MS/MS method. Results: We observed higher concentrations of remdesivir at C0 (6- to 7-fold higher than EC50 from in vitro studies) and a notable decay at C1. GS-441524 plasma concentrations reached a peak at C1 and persisted until the next administration. Higher concentrations of GS-441524 were observed in the patient with mild renal dysfunction. Mean BAS/plasma concentration ratios of GS-441524 were 2.3% and 6.4% in Patient 1 and Patient 2, respectively. The CSF concentration found in Patient 2 was 25.7% with respect to plasma. GS-441524 levels in lung and CNS suggest compartmental differences in drug exposure. Conclusions: We report the first pharmacokinetic evaluation of remdesivir and GS-441524 in recovered COVID-19 patients. Further study of the pharmacokinetic profile of remdesivir, GS-441524 and the intracellular triphosphate form are required.