Unit:
Library of the School of Health SciencesΤομέας Κλινικοεργαστηριακός
Dissertation committee:
Μελετιάδης Ιωσήφ, Επίκουρος Καθηγητής, Ιατρική, ΕΚΠΑ
Πουρνάρας Σπυρίδων, Καθηγητής, Ιατρική, ΕΚΠΑ
Mouton Johan, Professor, Medical School, Erasmus University Rotterdam
Ζέρβα Λουκία, Αναπληρώτρια Καθηγήτρια, Ιατρική, ΕΚΠΑ
Τσιόδρας Σωτήριος, Αναπληρωτής Καθηγητής, Ιατρική, ΕΚΠΑ
Τσιριγώτης Παναγιώτης, Αναπληρωτής Καθηγητής, Ιατρική, ΕΚΠΑ
Σιαφάκας Νικόλαος, Επίκουρος Καθηγητής, Ιατρική, ΕΚΠΑ
Original Title:
Optimizing antifungal therapy against azole-resistant Aspergillus fumigatus isolates using an in vitro pharmacokinetic/pharmacodynamic simulation model
Translated title:
Optimizing antifungal therapy against azole-resistant Aspergillus fumigatus isolates using an in vitro pharmacokinetic/pharmacodynamic simulation model
Summary:
The emergence of azole resistance raises concerns about first-line voriconazole treatment in high-risk patients with suspected invasive aspergillosis. Alternative therapeutic options are limited. A treatment strategy of growing interest for this difficult-to-treat infection is the combination of antifungals from distinct drug classes. The concentration-effect feature of this investigation could be amenable to pharmacokinetic/pharmacodynamic (PK/PD) modeling as this approach may provide important information regarding the outcome. Accurate and validated in vitro PK/PD models may serve as useful tools in order to quantitatively assess the efficacy of combination therapy, while they can be used to perform more comprehensive experiments compared to animal models and clinical trials.
In Chapter 2, a recently developed dynamic in vitro PK/PD model was evaluated based on the results obtained from a murine model of experimental aspergillosis using the same A. fumigatus strains and simulating mouse PK. Susceptibility breakpoints for voriconazole were then determined for different antifungal susceptibility testing methodologies applicable in the laboratory routine setting by simulating human PK and using A. fumigatus strains with distinct mechanisms of azole resistance. Moreover, the area under concentration-time curve (AUC) and trough levels of voriconazole in human serum required for optimal treatment and minimal toxicity were determined in relation to minimum inhibitory concentrations (MICs). The in vitro fAUC0-24/MIC associated with 50% antifungal activity was 28.61, close to the corresponding in vivo 14.67 fAUC0-24/MIC. Furthermore, the percentage target attainment was in agreement with the percentage efficacy in clinical trials of invasive aspergillosis in relation to CLSI MICs providing also a clinical correlation of the in vitro PK/PD model. The susceptible/ intermediate/resistant breakpoints were determined to be 0.25/0.5-1/2 mg/L for CLSI, 0.5/1-2/4 mg/L for EUCAST and 0.25/0.375-1/1.5 mg/L for gradient concentration strips. Hence, therapeutic drug monitoring could be used to optimize voriconazole therapy particularly against isolates with CLSI MICs of 0.5-1 mg/L and EUCAST MICs of 1-2 mg/L, targeting trough levels of 1 and 2 mg/L, respectively, whereas voriconazole should be avoided against isolates with CLSI and EUCAST MICs of >2 and >4 mg/L, respectively. Given the corroboration of the in vitro model with previous in vivo data, this tool may prove useful for predicting the in vivo outcome, while the determined susceptibility breakpoints and target values could assist in optimizing voriconazole therapy against A. fumigatus.
After having optimized and validated the in vitro PK/PD model, as it reliably simulated voriconazole PK in human serum and correlated with in vivo outcomes observed in animal models and clinical trials, it was adapted to accommodate two drugs with different half-lives, thus enabling the study of drug combinations. Particularly, in Chapter 3.1, human serum concentration-time profiles of amphotericin B (q24h) and voriconazole (q12h) administered concomitantly were simulated in the in vitro system and the PD interactions against azole-susceptible and -resistant A. fumigatus strains were studied using Bliss independence and canonical mixture response surface analyses. In vitro PK/PD combination data were then combined with human PK data using Monte Carlo analysis and both target attainment rate and serum levels of combination therapy regimens were calculated for isolates with different MICs. Concentration-dependent interactions were found: synergy was observed at low amphotericin B-high voriconazole exposures, whereas antagonism was found at high amphotericin B-low voriconazole exposures for all isolates. By bridging in vitro PK/PD combination data with human PK, combination therapy resulted in 17 to 48% higher target attainment rates than those of monotherapy regimens for isolates with voriconazole/ amphotericin B MICs of 1 to 4 mg/L. The PD target was attained for combination regimens with a 1.1 tCmin/MIC for voriconazole and a 0.5 tCmax/MIC for amphotericin B, while the equally effective monotherapy regimens required a voriconazole tCmin/MIC ratio of 1.8 and an amphotericin B tCmax/MIC ratio of 2.8. Therapeutic drug monitoring could be employed to optimize antifungal combination therapy with low-dose (≤0.6 mg/kg) amphotericin B-based combination regimens against resistant isolates for minimal toxicity.
In Chapter 3.2, the validated in vitro PK/PD model was used in order to investigate the PD effects of voriconazole/anidulafungin combination against A. fumigatus, including azole-resistant isolates, simulating human serum concentration-time profiles of standard and lower dosages of anidulafungin. PD interactions were assessed using Bliss independence analysis and Loewe additivity-based canonical mixture response-surface non-linear regression analysis. Target serum levels of combination regimens were determined for isolates with increasing MICs and target attainment rates were calculated for centers with different resistance rates using Monte Carlo analysis. Exposure- and MIC-dependent interactions were revealed: synergy was found at low anidulafungin (fCmax/MEC <10) and voriconazole (fAUC/MIC <10) exposures, whereas antagonism was observed at higher drug exposures. The largest increase in the probability of target attainment was found with 25 mg of anidulafungin and voriconazole MIC distributions with high (>10%) resistance rates, indicating that the combination of voriconazole with low-dose anidulafungin may increase the efficacy and reduce the cost and potential toxicity of antifungal therapy, particularly against azole-resistant A. fumigatus isolates and in patients with subtherapeutic serum levels.
Based on the aforementioned results, therapeutic drug monitoring plays a critical role in the optimization of antifungal combination therapy, while its clinical use and value are related to accurate, rapid and cost-effective assays. Bioassays are frequently adopted and routinely performed because of their relative technical simplicity and low consumable and equipment costs. To date, there are no microbiological assays for measuring voriconazole serum concentration in patients on antifungal combination therapy for difficult-to-treat fungal infections. Hence, in Chapter 3.3 voriconazole levels were determined with high-performance liquid chromatography (HPLC) and a new microbiological agar diffusion assay in 103 serum samples from an HPLC-tested external quality control program (n=39), 21 patients receiving voriconazole monotherapy (n=39), and 7 patients receiving voriconazole-echinocandin combination therapy (n=25). The results of the bioassay were highly correlated with the HPLC results (Spearman's rank correlation coefficient >0.93, % difference <12 ± 3.8%). This is the first report in literature of a bioassay that can be used for measuring voriconazole serum concentration in the presence of echinocandins giving comparable results to HPLC.
Main subject category:
Health Sciences
Keywords:
Azole-resistant aspergillosis, Voriconazole, Combination therapy, In vitro pharmacokinetic/pharmacodynamic model
Number of references:
371
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