Powder reservoir systems

The metering of DPIs is closely linked to the device itself and may be divided into three common systems (27) capsules, multidose blister packs, and powder reservoir systems. The considerations that go into these metering systems include convenience to the patients, stability on storage, compatibility with product, and ease of filling. 

The development of multidose DPIs was pioneered by A. B. Draco (now a division of AstraZeneca) with their Turbuhaler [53]. This device is truly a metered-dose powder delivery system. The drug is contained within a storage reservoir and can be dispensed into the dosing chamber by a simple back-and-forth twisting action on the base of the unit (Fig. 7). The device is capable of working at moderate flowrates and also delivers carrier-free particles [54]. However, one of the drawbacks of the Turbuhaler has been the fact that it has... 

Fig. 4.3.1 (a) Photographs of a tubeless siphon formed by dissolving 0.5%w/v poly (ethylene oxide) powder in tap water, where a Fano column can be seen between the tip of the glass pipette at the top and fluid reservoir at the bottom, (b) Excess fluid can be seen just below the fluid entrance, (c) A large amount of excess fluid eventually flows downwards outside and along the Fano column, which can disturb the vertical location of the column. These figures illustrate the fact that there is an optimum volume flow rate for a particular flow system. 

Figure 49 shows a recent experimental device, developed by Schubert, which uses the principle of Figure 45(f). The force is created by water which flows slowly into a container (1) from a reservoir (2). In this apparatus two tests can be carried out on the same sample and, if moist agglomerates are investigated, the capillary pressure can be measured simultaneously by means of a U-tube manometer (3). Penetration of powder into the manometer is prevented by a suitable filter (4). Since the equilibrium capillary pressure develops only after a certain period of time, the system can be covered with a plate (5) to avoid evaporation of the liquid. The apparatus has been further perfected by installation of very sensitive inductive linear transducers (7) after fixation of one side with a set screw (6) the expansion in the sample near the predetermined failure plane can be measured prior to the break. 

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