An optimal antifungal therapy for invasive candidiasis in critically ill patients is essential to reduce the high mortality rates. Acute kidney injury is common, and continuous renal replacement therapies are frequently used. Previous studies have demonstrated a lack of effect from different continuous renal replacement techniques on micafungin clearance. However, the use of high cutoff pore size membranes could potentially allow for the loss of albumin and alter micafungin pharmacokinetics. The objective was to explore the pharmacokinetics of micafungin in critically ill patients undergoing continuous venovenous high cutoff membrane hemodialysis (CVVHD-HCO). Prospective observational study performed in critically ill patients treated with 100 mg/d of micafungin and undergoing CVVHD-HCO. CVVHD-HCO sessions were performed using Prisma-Flex monitors and dialyzers with a membrane of polyarylethersulfone of 1.1-m surface area and 45-kDa pore size. Blood samples were collected from arterial prefilter, venous postfilter, and the drainage line ports at 0 (predose), 1, 4, 12, 24 hours after dose, and micafungin concentrations were determined using HPLC-UV. Nine patients (55.6% male; age: 28-80 years) were included. Median (range) of micafungin concentrations in the effluent were <0.2 (<0.2-0.4) mg/L at low (predose) and 0.4 (<0.2-0.7) mg/L at high (1 h) concentrations. The extraction ratio was <12% at each time point. A 2-compartment model best described the time course of plasma concentrations, and body weight was the only covariate that improved the model. This is the first study demonstrating that CVVHD-HCO does not alter the pharmacokinetics of micafungin, and that standard doses of this antifungal can be used.