Intragastric distribution of ion-exchange resins: a drug delivery system for the topical treatment of the gastric mucosa

Previous studies by this group on freeze-dried oral dosage forms containing finely-divided ion-exchange resins revealed prolonged gastric residence and uniform distribution within the stomach. The present study was carried out to ascertain whether this was due to freeze-drying, properties of the radiolabelled ionic exchange resin, or the small dosing volume used. 99mTc-labelled cholestyramine resin was administered in two dosage forms, a freeze-dried tablet which dissolved in the oral cavity (orally dissolving tablet; ODT) and a 1.5 mL aqueous suspension. Two resin particle sizes (20-40 and 90-125 microns) were studied. Oesophageal transit and intragastric distribution and residence were followed by gamma scintigraphy. In a second study, in six subjects, gastric emptying of the water-soluble fraction of the ODT and 1.5 mL of water, was measured using 99mTc diethylenetriaminepentaacetic acid. Oesophageal transit of a water-soluble marker and resin in suspension was rapid, but the transit of the resin in the ODTs was significantly prolonged. Regardless of particle size or dosage form, the resin was evenly distributed throughout the stomach with 20-25% remaining for 5.5 h. In contrast, the water-soluble marker cleared from the stomach rapidly from both dosage forms. We suggest that oral dose forms containing finely-divided ion-exchange resins may form a useful system for topical treatment of the gastric mucosa, for example in targeting to Helicobacter pylori infection.