Polyanionic hydrogel as a gastric retentive system.
Gastric emptying of a polyanionic hydrogel, polycarbophil (PC), from the canine stomach was studied using a duodenal cannulation technique. The basis of the study is to employ a certain quantity of swelling hydrogel that, by virtue of its swollen size and viscosity, converts a fasted stomach to a fed state and resists discharge from the stomach for an extended period of time. Different amounts of PC, in 200 ml water plus buffering agents, were administered orally to fasted canines. The gastric emptying lag time was found to increase with the viscosity of the administered dose. Addition of a base, sodium bicarbonate, to PC increased gastric retention via an increase in its apparent viscosity. The polymer mass is retained in the canine stomach until a sufficient quantity of stomach acid secretion reduces the viscosity of the viscous mass, through protonation of polycarbophil, and, at that point, discharge of the hydrogel will commence. Thus, gastric retention of PC hydrogel in the canine stomach can be prolonged by increasing the apparent viscosity of the hydrogel administered.