Dry powder inhalers-
Dry powder inhalers (DPIs) are breath-actuated devices, by virtue of the fact that the kinetic energy imparted to the drug comes from the patient inhaling. The basic construction of all DPIs consists of mouthpiece and a turbulence chamber for dispersing the drug into the air stream. To reduce the incidence of agglomeration, the active material is normally loosely bound to a longer carrier such as lactose. A metered dose of the drug is introduced into the chamber from its storage area, which can be bulk, capsules or blister form. The patient then inhales and the resulting turbulence possibly assisted by mechanical agitation disperses the powder into the air stream and separates the drug from the carrier. Continued inhalation carries the drug into the airways where deposition occurs. Because of design constraints in order to achieve optimum dispersion, airflow rates through the device have to be relatively high = 60 L/min. Because of high air flows mean and high flow velocities, the inertia of the particles is higher and the resulting deposition in the upper airways in higher.
This area is probably best reviewed by considering the possible developments within each group.
Intrapulmonary and Endotracheal Routes of Administration :
According to current guidelines recommended for the management of cardiac arrest, the American Heart Association has recommended that when intravenous or intraosseous routes cannot be established, endotracheal administration of some resuscitation drugs be used. Medications that can be absorbed through the trachea include lidocaine, epinephrine, atropine, naloxone, and vasopressin (American Heart Association [AHA], 2005). Although the optimal dose of these drugs has yet to be established, two to two and one half times the recommended intravenous dose is used (AHA, 2005).
Recent studies investigated the intrapulmonary route of drug administration. One study suggests that intrapulmonary vancomycin may have efficacy in acute lung injuries, such as meconium aspiration syndrome in neonates (Jeng, Lee, & Soong, 2007). Televancin is also being studied for intrapulmonary use. Because the antibacterial activity is not affected by pulmonary surfactant, further studies of intrapulmonary televancin for use in treating gram-positive respiratory infections are underway (Gotfried et al., 2008).
Nebulisers, by virtue of their design and their need for an external energy source, tend in the main to be bulky and expensive and because of longer treatment period come low on social acceptability scale. Work in this area is likely to be directed towards smaller, most compact, low cost units suitable for home use. Metered dose inhalers represent a field in which developments are currently taking place. Continued interest is being shown in innovations on BAIs and spacer chamber based MDI. Dry powder inhalers will continue to appear in the market place in new and improved forms, the main areas of improvement being in the airflow/dispension chambers and the drug storage systems, the main objective being ease of use.
In the next chapter, let us discuss mucosal DDS by the intra nasal route.
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Dry powder inhalers-
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