Influence of Ionic Strength on the pH-sensitive in vitro Ibuprofen Release from Dextran-poly(acrylic acid) Copolymer

Abstract

The effects of cations and pH on the in vitro ibuprofen release from dextran-poly(acrylic acid) copolymer were investigated at varying pH and Na+ or Ca2+ concentrations. These results revealed that ibuprofen release was strongly depended on the acidic and basic environments, in which, the cumulative amount released in 24 h reached up to 87 % at pH 2.0 but only 32 % at pH 7.4, respectively, demonstrating a good pH-dependency. However, cations in release solution exerted a remarkable influence on ibuprofen release, especially in the acidic media. Meanwhile, ibuprofen release rate decreased with increasing strength of Na+, Ca2+ and NaCl concentration. The zeta potential profiles and particle distributions at different ionic strengths indicated that cations strongly influence ibuprofen release performance, through surface charge, hydrogen bonding, and electrostatic interactions in and between the polymer and ibuprofen. These results suggested that Na+ and Ca2+ strength exerted a profound influence on the pH-sensitive in vitro ibuprofen release from the dextran-poly(acrylic acid) copolymer.