Floating Doses

Gastro-retentive principles and mechanisms are considered in another chapter. Floating dosage forms comprise low-density materials or those that rapidly lower

Fig. 9.1 Schematic of the stomach showing retention of a floating dosage form

Oesophagus

Pyloric sphincter region

Oesophagus

Floating dose

Stomach content

Floating dose

Stomach content

Fig. 9.2 Osmotic core pulsed release pellets

Drug-containing swellable osmotic core

Drug-containing swellable osmotic core

Semipermeable membrane

Water ingress

Semipermeable membrane

Water ingress their density to enable buoyancy in the stomach contents and increase gastric residence (Fig. 9.1). Residence can be terminated by increasing the density of the floating device or by complete emptying of the stomach contents. Low-density polyvinyl pyrrolidone [60], low-density hollow polycarbonate microspheres [61], and rapidly swelling porous hydrogel composites [62], have all exhibited flotation. However, none have been effectively developed to a PDD system. Sigmoidal release profiles have been achieved using low-density calcium alginate beads [63, 64]. These are insoluble in the stomach [65], and dissolve as the pH rises in the small intestine.

A true PDD has been achieved by using an effervescent core to generate carbon dioxide to produce a low-density polymeric coated tablet [66]. The device remained intact until a semipermeable film ruptured after a certain lag time followed by a pulse release of drug.

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