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Figure 5.20 The effect of pellet density and size of a meal on the gastric emptying of multiparticulates to have adhered to the mucosa, but to have formed large intragastric boluses. Apparently that the slow rate of emptying of the polycarbophil was due to the action of the stomach squeezing the particles together, causing a loss of surface-bound water and forming a large bolus; occasional retropulsion mixed the bolus with the gastric secretions causing some redispersion of particles. The gastric distension produced by the large indigestible mass elicited the fed pattern of activity and the fasting peristaltic waves were suppressed.
Another gastroretentive system is the magnetic dose form. This usually contains a magnet, or a mass of magnetic material such as a ferrite, in its centre and an externally placed magnet serves to anchor the dose form within the body. Drugs which have been delivered by this method include cinnarizine, acetominophen and riboflavin, all of which showed improved bioavailability. The major drawback with this method is that placing the external magnet to hold the tablet in the stomach is technically quite difficult. To make magnetic tablets commercially viable a better method for applying the magnetic field needs to be produced than that currently available.
Dose forms that unfurl or expand in the stomach, becoming too large to exit through the pylorus, have also been proposed to achieve prolonged gastric residence. Geometric shapes which have been studied include a continuous solid stick, a ring and a planar membrane. In fasted beagle dogs retention times of over 24 h were reported91, but in humans the time was reduced to 6.5 h in the fed state and 3 h in the fasted state. The main problems with this type of system is that they have to exit the stomach eventually, and hence have to be biodegradable as well as having expanding properties. This can pose severe design restrictions. In addition, like all sustained release devices, the systems would have to have a high reliability since they would be designed to administer a large dose of drug over an extended period. Adhesion of dosage form to the oesophagus is common, and the possibility of a device sticking and expanding in the oesophagus is unpleasant to say the least. Swellable systems would also have to be able to withstand the 80 to 100 mmHg pressures generated in the human pylorus22 92. These combined difficulties have outweighed any potential advantaged for manufacturers to date.
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Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...