Intracellular concentrations of micafungin in different cellular compartments of the peripheral blood

Whilst micafungin serum concentrations are well studied, little is known about its concentrations within cellular compartments of the peripheral blood. Hence, in this study blood samples were collected from patients receiving micafungin (n = 26). These samples were separated by double-discontinuous Ficoll-Hypaque density gradient centrifugation. Intracellular concentrations within the obtained cells, i.e. peripheral blood mononuclear cells (PBMCs), polymorphonuclear leukocytes (PMNs) and red blood cells (RBCs), were determined by liquid chromatography–tandem mass spectrometry (LC–MS/MS). Within PBMCs and PMNs, the intracellular micafungin concentration was significantly increased compared with the concentration in plasma (P < 0.001). The intracellular concentration within RBCs did not significantly differ from the plasma concentration. Micafungin reaches high concentrations in human PBMCs and PMNs and is present in RBCs. In vitro data showed that intracellular uptake of micafungin by PBMCs depends on the albumin concentration of the surrounding medium, but only at non-physiological protein concentrations.