Carboxymethyl guar gum (CMGG), an anionic semisynthetic GG derivative, was synthesized by incorporating CM group into GG chain. Microspheres were prepared by loading abacavir sulfate (AS) using water-in-oil (w/o) emulsion method. Formulations were characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), X-ray diffraction (XRD), thermogravimetry (TGA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). In vitro release profiles of GG and CMGG loaded with AS performed in pH 1.2 as well as 7.4 buffer media at 37 degrees C displayed the varying drug release profiles in stomach and intestinal conditions. Release of the drug was extended up to 28 h in both GG and CMGG matrices, but the burst release observed in case of GG matrix was reduced in the case of CMGG. The kinetics of in vitro release was analyzed using the empirical equations. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122:452-460, 2011