AbstractBackgroundVoriconazole exhibits in vitro activity against Candida glabrata and Candida krusei (EUCAST/CLSI epidemiological cut-off values 1/0.25 and 1/0.5 mg/L, respectively). Yet, EUCAST found insufficient evidence to set breakpoints for these species. We explored voriconazole pharmacodynamics (PD) in an in vitro dynamic model simulating human pharmacokinetics (PK).MethodsFour C. glabrata and three C. krusei isolates (voriconazole EUCAST and CLSI MICs of 0.03–2 mg/L) were tested in the PK/PD model simulating voriconazole exposures (t½ ∼6 h q12h dosing for 3 days). PK/PD breakpoints were determined calculating the PTA for exposure indices fAUC0–24/MIC associated with half-maximal activity (EI50) using Monte Carlo simulation analysis.ResultsFungal load increased from 3.60 ± 0.35 to 8.41 ± 0.24 log10 cfu/mL in the drug-free control, with a maximum effect of ∼1 log10 kill of C. glabrata and C. krusei isolates with MICs of 0.06 and 0.25 mg/L, respectively, at high drug exposures. The 72 h log10 cfu/mL change versus fAUC0–24/MIC relationship followed a sigmoid curve for C. glabrata (R2=0.85–0.87) and C. krusei (R2=0.56–0.76) with EI50 of 49 (32–76) and 52 (33–78) fAUC/MIC for EUCAST and 55 (31–96) and 80 (42–152) fAUC/MIC for CLSI, respectively. The PTAs for C. glabrata and C. krusei isolates with EUCAST/CLSI MICs ≤0.125/≤0.06 mg/L were >95%. Isolates with EUCAST/CLSI MICs of 0.25–1/0.125–0.5 would require trough levels 1–4 mg/L; isolates with higher MICs would not attain the corresponding PK/PD targets without reaching toxicity.ConclusionsThe in vitro PK/PD breakpoints for C. glabrata and C. krusei for EUCAST (0.125 mg/L) and CLSI (0.06 mg/L) bisected the WT populations. Trough levels of >4 mg/L, which are not clinically feasible, are necessary for efficacy against WT isolates.