Inhalation route of administration
Routes of Administration
The inhalation route requires the active ingredient to pass through the upper respiratory tract, up to the alveolar level (the deepest point of the respiratory system). The alveoli are in close contact with the endothelium of the blood capillaries, allowing gas exchange and "absorption of the active ingredient. The absorbent surface in the alveoli is approximately 90 m2.
The inhalation route is very useful because a local action or a systemic effect can be obtained. In the first case the active principle is deposited on the mucous membrane of the trachea or bronchi, thus carrying out the anti-inflammatory effect (eg. inflammation of the trachea or bronchi). In the case of a systemic effect, the active ingredient is instead absorbed and released into the bloodstream.
The drug can already be found in a gaseous state (like anesthetics), vaporized with the aid of special nebulizers, or reduced to very small particles through the aerosol.
Administration by inhalation takes place in the form of aerosols (liquid particles) or powders (solid particles).
Absorption is favored by a high exchange surface, high spraying and a very thin membrane thickness. In both cases, the hepatic filter is skipped; therefore the first pass effect is lacking in inhaled administration.
The size of the particles that we obtain with an aerosol or with a nebulization is very important, because according to the size of these particles different areas of the respiratory system can be reached. The larger the particles, the lower the depth reached, and vice versa. In particular, particles with a size greater than 5 μm will stop at the level of the upper respiratory tract, while particles with a size less than 1-2 μm, once taken by inhalation, can reach the alveolar level where they will be absorbed. In the case of aerosols and powders, the fate of the particles therefore depends on their diameter:
- > 5 μm: deposited in the upper airways
- 1-5 μm: deposited in the tracheo-bronchial tree. The soluble ones can be absorbed by the respiratory tract cells and produce local action, the insoluble ones are removed by the movement of the cilia (mucociliary clearance), carried into the pharynx and ingested.
- <1 μm: they reach the alveoli where they are absorbed, causing systemic action.
Other articles on "Inhalation route of administration"
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