Intranasal

With intranasal delivery, a solution is applied to the respiratory and olfactory epithelium lining the nasal cavity; this thin mucosa, rich in blood vessels, lets substances pass straight into the systemic circulation without a first pass through the liver. In humans the total absorbing surface is only around 150 cm², and mucociliary clearance moves deposited fluid toward the throat within about fifteen to twenty minutes, so there is little time for absorption.

Why researchers use this route

Two features make it attractive. Firstly, skipping first-pass metabolism gives many peptides higher bioavailability than the oral route, although values stay well under subcutaneous figures and depend strongly on the formulation. Secondly, the olfactory and trigeminal nerve pathways may provide a route into the central nervous system that bypasses the blood-brain barrier; this idea has been explored in animal studies and small human studies of oxytocin, insulin and the Russian regulatory peptides, and the evidence is still under active debate rather than resolved.

The formulation is the bottleneck. Research sprays are water-based solutions containing a preservative and a tonicity agent, usually releasing 50 to 100 µL per actuation, and once mixed they rely on the chosen excipients for stability. See our nasal spray formats, the Semax nasal spray listing and the nasal spray formulation guide.

Related terms

hydrophilic · nasal spray reconstitution kit