Membrane formation and drug loading effects in high amylose starch tablets studied by NMR imaging

Cross-linked high amylose starch is used as an excipient in the preparation of pharmaceutical tablets for the sustained release of drugs. NMR imaging with contrast enhanced by proton density and by self-diffusion coefficient was used to follow the water uptake and swelling, two critical parameters controlling the drug release of the cross-linked starch tablets containing 10 wt % of ciprofloxacin and of acetaminophen, respectively. The drug-loaded tablets were studied in a H2O/D2O mixture at 37 degrees C in comparison to the tablets without any drug loading. The diffusion of water in the tablets all showed a Fickian behavior, but the kinetics of water uptake was faster in the case of the drug-loaded tablets. The formation of a membrane at the water/tablet interface was observed.