The influence of Pluronics L64, F68, F88 and F127 on the solubility and membrane permeability of leflunomide (LEF) in acidic and alkaline buffer solutions with physiological pHs was revealed. A noticeable increase of LEF solubility in the presence of Pluronics was revealed. It was demonstrated that the structure of Pluronics has influence on the manifestation of a solubilizing effect. Namely, more efficient solubilizers for LEF were found to be L64 and F127, having the lowest content of ethylene oxide groups in the structure and lower HLB indices in comparison with F68 and F88. The binding of LEF with the core of Pluronic micelles was proposed on the basis of the obtained 1Н NMR data. Permeability of LEF through an artificial Permeapad barrier composed of phospholipids was measured using the Franz diffusion cell. Decrease of the LEF permeability in the presence of all investigated Pluronics was detected. The location of hydrophobic fragment of LEF molecule inside the micelle leads to a decrease in the non-polar surface area and the ability of the drug to pass through the lipophilic layer of the membrane.
