Improving Ibuprofen solubility by surfactant-facilitated self-assembly into mixed micelles

Ibuprofen is a poorly water-soluble drug, characterized by dissolution-limited oral bioavailability. One approach to improve its water solubility and bioavailability is by solubilizing it in micellar surfactant solutions. Here we investigate the effect of the surfactant type and the mechanism of solubility enhancement of Ibuprofen in surfactant solutions. The equilibrium Ibuprofen solubility in solutions of six surfactants was determined by HPLC. The nonionic surfactant polysorbate 80 (Tween 80), and the anionic surfactants sodium dodecyl sulfate (SDS) and sodium lauryl ethoxy (3) sulfate (SLES-3EO) improve the Ibuprofen solubility by a factor of 200, as compared to the solubility in water. The highest Ibuprofen solubility is observed in SDS and SLES-3EO solutions, containing 0.6 M NaCl. The mole fraction of Ibuprofen in the micelles and the transfer energy of Ibuprofen molecules from the aqueous phase into the micelle environment were determined by thermodynamic analysis of the solubility data. The maximum Ibuprofen mole fraction in the micelles of all studied surfactants is exceptionally high (between 0.4 and 0.6). Thus we can conclude that the main mechanism of Ibuprofen solubility enhancement is self-assembly within mixed micelles with the main surfactant. The energy of co-micellization is estimated to be around 14 kT per Ibuprofen molecule.