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.