Gastric Retentive Strategies Expandable Dosage Forms

Expandable GRFs are designed to expand to a sufficient physical size and strength to prevent being compressed and pushed through the pylorus. After being retained in the stomach for the desired length of time, the GRF should weaken and/or decrease in size to enable it to be cleared from the stomach. Size and strength attributes of such a GRF providing gastric retention are not explicitly known at this time. Evidence from the endoscopic literature regarding the ingestion of large objects, or formation of gastric bezoars, suggests that a GRF must be fairly rigid and of a size larger than 5 cm long and 2 cm in diameter [34-36]. These physical attributes of size and strength are necessary for a GRF to withstand being expelled from the stomach during a Phase III contraction (i.e. housekeeper wave) of the migrating motor complex.

Several different expansion strategies have been explored, with some being marketed as GRFs. However, to our knowledge, no expandable GRF has offered a significant advantage over a large, nondisintegrating tablet taken with food. The case study which concludes this chapter offers a new addition to the literature in regard to expandable dosage forms failing to cross the "valley of death."

Fig. 17.6 SEM of attachment organs of some parasites. Scale bar is 100 mm. Reproduced with permission from Whittington et al. [32]

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