Dose optimization of voriconazole/anidulafungin combination against Aspergillus fumigatus using an in vitro pharmacokinetic/pharmacodynamic model and response surface analysis: clinical implications for azole-resistant aspergillosis

<span class="paragraphSection"><div class="boxTitle">Background</div>Combination therapy of voriconazole with an echinocandin is often employed in order to increase the efficacy of voriconazole monotherapy.<div class="boxTitle">Methods</div>Four clinical <span style="font-style:italic;">Aspergillus fumigatus</span> isolates with different <span style="font-style:italic;">in vitro</span> susceptibilities to voriconazole (MIC 0.125–2 mg/L) and anidulafungin (MEC 0.008–0.016 mg/L) were tested in an <span style="font-style:italic;">in vitro</span> pharmacokinetic/pharmacodynamic model simulating human serum concentrations of standard dosages of voriconazole and anidulafungin. Fungal growth was assessed using galactomannan production and quantitative PCR. Drug concentrations were determined with bioassays. Pharmacodynamic interactions were assessed using Bliss independence analysis (BI) and Loewe additivity-based canonical mixture response-surface non-linear regression analysis (LA). Probability of target attainment (PTA) was estimated with Monte Carlo analysis for different doses of anidulafungin (25, 50 and 100 mg) and azole resistance rates (5%–25%).<div class="boxTitle">Results</div>Synergy [BI 51% (8%–80%), LA 0.63 (0.38–0.79)] was found at low anidulafungin (<span style="font-style:italic;">fC</span>_max/MEC <10) and voriconazole (<span style="font-style:italic;">f</span>AUC/MIC <10) exposures, whereas antagonism [BI 12% (5%–18%, LA 1.12 (1.04–4.6)] was found at higher drug exposures. The largest increase in PTA was found with 25 mg of anidulafungin and voriconazole MIC distributions with high (>10%) resistance rates. PTAs for isolates with voriconazole MICs of 1, 2 and 4 mg/L was 78%, 12% and 0% with voriconazole monotherapy and 96%–100%, 68%–82% and 9%–20% with combination therapy, respectively. Optimal activity was associated with a voriconazole <span style="font-style:italic;">tC</span>_min/MIC ratio of 1.5 for monotherapy and 0.75 for combination therapy.<div class="boxTitle">Conclusions</div>The present study indicated 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 <span style="font-style:italic;">A. fumigatus</span> isolates and in patients with subtherapeutic serum levels. This hypothesis warrants further <span style="font-style:italic;">in vivo</span> verification.</span>

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