Olfactory Transfer
The major part of the approximately 150 cm2 surface in the human nasal cavity is covered by respiratory epithelium, across which systemic drug absorption can be achieved. The olfactory epithelium is situated in the upper posterior part and covers approximately 10 cm2 of the human nasal cavity. The nerve cells of the olfactory epithelium project into the olfactory bulb of the brain, which provides a direct connection between the brain and the external environment. The transfer of drugs to the brain from the blood circulation is normally hindered by the blood–brain barrier (BBB), which is virtually impermeable to passive diffusion of all but small, lipophilic substances. However, if drug substances can be transferred along the olfactory nerve cells, they can bypass the BBB and enter the brain directly.,
The olfactory transfer of drugs into the brain is thought to occur by either slow transport inside the olfactory nerve cells to the olfactory bulb or by faster transfer along the perineural space surrounding the olfactory nerve cells into the cerebrospinal fluid surrounding the olfactory bulbs and the brain (8, 9)
Olfactory transfer could theoretically be used to deliver drugs that have a required effect in the central nervous system such as those for Parkinson’s or Alzheimer’s diseases. Studies have been presented that show that direct transfer of drugs is achievable but the possibility of olfactory delivery of therapeutically relevant doses to humans remains to be demonstrated.
Read more about this topic: Nasal Administration
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