Sprays, MDIs, Aerosols
Intranasal inhalations are administered to achieve either local respiratory or systemic therapeutic benefits. Special devices, such as the plastic spray bottle or bottles with metered dose valves, are used to break up a solution preparation into small particles and deliver a spray.
Some active drugs are administered using pressurized intranasal aerosols (i.e., an intranasal aerosol inhaler). The advantages and disadvantages of the intranasal aerosols are the same as those of the inhaled aerosols administered through the mouth.
The one-way nasal pumps (i.e., MDIs in bottles) prevent drawback contamination of nasal fluids into the bottle after administration.
Other drugs are packaged in nebules and administered tbrough nebulizers as "inhalation therapy." The nebulizers dispense the drug particles into the 0.5-5.0 µm range, which is the optimum particle size for inhalation administration. The particles in the optimum particle size range are carried out of the nebulizer in a mist; the larger particles do not exit the device, but fall back into the reservoir of medication to be re-nebulized.
If the drug is sufficiently volatile, it can be administered
via a nasal inhaler. The inhaler is a capped cylindrical tube that contains
fibrous material impregnated with a volatile drug. The patient removes the cap
and the inhaler tip is placed just inside the nostril. As the patient inhales,
air is pulled through the tube and the vaporized drug is pulled into the nasal
Loss of Drug During Administration
Even through there are several different dosing devices for intranasal administration, the drug can still be lost following administration by three mechanisms:
- Metabolism in the nasal
mucosa. The nasal mucosa
is an enzymatically active tissue; some drugs are significantly degraded
when administered by this route.
- Mucus flow and ciliary
movement. The normal physiology
of the nasal cavity is to move mucus and inhaled contaminants up and away
from the lungs and toward the orifice of the nose. Some drug loss will
occur as the drug is swept outward by these processes.
Intranasal administration can also cause the drug to be swallowed and in some
cases enough drug will be swallowed to be equal to an oral dose. This may
lead to a systemic effect from the drug even though it is intranasally administered.