Introduction to Intranasal Absorption

There are many factors that affect the delivery of a drug to blood circulation and the central nervous system. The nasal passageways are highly vasularized which aids in the absorption of drug via IN administration, but drug factors such as solubility, stability, molecular weight, and hydrophobicity affect absorption. [3][4]

Intranasal Absorption's Path to Systemic Circulation

When a drug in insufflated the material makes contact with the epithelial cells of the nasal membranes when it dissolves or mixes in the mucous. A drug can then be absorbed by one of two pathways, transcellular transport and paracellular transport. A drug that enters the body transcellularly passes into and through the cells that make up the membrane, and paracellular transport refers to a drug which enters the body between cells, in the paracellular space, where tight junctions hold the cells together and prevent some molecules from passing into the tissue. On a side note, typical capillaries contain gaps that allow for the free flow of substances out and into the blood, while capillaries in the brain contain tight junctions to prohibit many drugs and other substances from leaking into the tissue and surrounding neural cells.
Hydrophobic molecules of a low molecular weight tend to enter the tissue via the transcellular pathway, while hydrophilic molecules generally enter via the paracellular pathway, and the latter is also possible when a drug is prepared in such a way that the tight junctions are opened. For the majority of recreational substances, lipophilicity is the most important factor determining their absorption. Larger molecules such as peptides may interact with glycoprotein chains in the mucus and this could pose a barrier. Fat soluble compounds can permeate the cell bilayer and right into the cell in the nasal membrane. It was also determined that low molecular weight compounds like para-aminohippuric acid also passed into the tissue quite easily as well. [4]

Advantages of Intranasal Absorption

Disadvantages of Intranasal Absorption

One of the major disadvantages of intranasal administration is the propensity to cause irritation to the mucous membranes of the sinus cavity. Depending on the chemical being administered, there's a significant chance that irritation will occur. Over time, repeated IN administration can wear away the septum (a thin layer of tissue between the nostrils that separates the sinus cavities) causing a perforation. Even occasional IN administration can cause one to be "stuffed up", as some of the inactive ingredients in certain pharmaceuticals are both irritating and unable to cross the phospholipid bilayer into direct circulation. Chronic sinus infections and tissue damage resulting from either the drug itself or binders & fillers aren't uncommon among those who opt for IN administration.

Materials Required for Intranasal Absorption

Rolled up money note
Straw
Snuff snorter

Safety Precautions Involving Intranasal Absorption

The Dangers of Intranasal Absorption

Intranasal Absorption