Modified guar gum matrix tablet for controlled release of diltiazem hydrochloride

Polyacrylamide-grafted-guar gum (pAAm-g-GG) was prepared by taking three different ratios of guar gum to acrylamide (1:2, 1:3.5 and 1:5). Amide groups of these grafted copolymers were converted into carboxylic functional groups. Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry were used to characterize copolymers. Tablets were prepared by incorporating an antihypertensive drug viz., diltiazem hydrochloride. In-vitro drug release was carried out in simulated gastric and intestinal conditions. Effect of drug loading on release kinetics was evaluated. Release continued up to 8 and 12 h, respectively, for pAAm-g-GG and hydrolyzed pAAm-g-GG copolymers. Nature of drug transport through the polymer matrices was studied by comparing with Higuchi, Hixson-Crowell and Kopcha equations. Drug release was found to be dissolution-controlled in case of unhydrolyzed copolymer. With hydrolyzed copolymers, drug release was swelling-controlled initially (i.e., in 0.1 N HCl), but at later stage, it became dissolution-controlled in pH 7.4. Hydrolyzed pAAm-g-GG matrices are pH sensitive and can be used for intestinal drug delivery.