nasal delivery

Nasal delivery puts a drug onto the moist lining inside the nose, either to act locally (like a decongestant or allergy spray) or to be absorbed into the bloodstream. The nose is a surprisingly good absorption surface: it is thin, richly supplied with blood vessels, and reached without a needle, so for some drugs a sniff can rival an injection for speed.

The nasal mucosa is well perfused and relatively permeable, and because the absorbed drug enters the systemic circulation directly it bypasses first-pass liver metabolism. Most products are aqueous sprays delivered by a metered pump that produces droplets large enough (typically tens of micrometres) to deposit in the nose rather than be inhaled into the lungs. A special bonus is the olfactory region high in the nose, which offers a possible direct nose-to-brain pathway for some central-nervous-system drugs, though how much this contributes in humans is debated.

The main limitation is the nose's own defence: mucociliary clearance constantly sweeps the lining toward the throat, giving a drug only minutes to be absorbed before it is swallowed. Volume is also limited (only about 100–150 µL per nostril stays put; more just drips out), and irritation, a runny or blocked nose, and variable absorption can all reduce reliability. Mucoadhesive formulations and permeation enhancers are used to extend contact time and uptake.