Nasal administration refers to the absorption of drugs across the nasal mucosa, i.e. not accessing to the respiratory tract. It is a form of administration that can be used for both local and systemic therapies and is presented as an alternative, non-invasive route, especially useful in the case of extensively metabolized or labile drugs in the GI medium. Absorption into the systemic circulation occurs through the nasal-associated lymphoid tissue.
The nasal cavity begins in the nostrils, which gather and direct the entrance of air. Behind them is the region containing the turbinates and nasal epithelium and then the nasopharynx, where ends the septum that divides the nasal cavity into two halves and so the cavity becomes one.
The nasal mucosa is a very vascularized and easily accessible area, with a nonkeratinized epithelium composed by ciliated cells, as well as mucous glands and goblet cells, responsible for producing and storing nasal mucus.
This article focuses on the advantages and disadvantages of nasal route of drug administration.
1. High permeability of the nasal mucosa compared to the epidermis or the gastrointestinal mucosa.
2. Highly vascularized subepithelial tissue.
3. Rapid absorption, usually within half an hour.
4. Avoidance of first-pass effect that occurs after absorption of drugs from the gastrointestinal tract.
5. Avoidance of the effects of gastric stasis and vomiting, for example, in migraine patients.
6. Ease of administration by the patients who are usually familiar with nasal drops and sprays.
8. Most feasible route for the delivery of peptides.
1. Nasal drug administration is limited, however, to very small volumes (25–200 μL), and thus only applicable to potent drugs with high water solubility.
2. The active ingredient must have a molecular weight <1 kDa to be absorbed.
3. Nasal route of drug administration is not suitable for drugs that are irritating or injurious to the nasal mucosa.
4. Diseases conditions of the nose may result in impaired absorption.
5. Dose is limited due to relatively small area available for absorption.
6. Compounds that reach the nasal epithelium rarely achieve prolonged contact times with the cells surface due to the presence of the mucus that cover the mucosa, which is constantly propelled by the cilia of epithelial cells. When this periciliary fluid interacts with the airflow, foreign compounds in the air are forced to move into the nasopharynx until they are swallowed, in a process named mucociliary clearance
7. Little is known of the effect of common cold on transnasal drug delivery, and it is likely that instilling a drug into a blocked nose or a nose with surplus of watery rhinorrhea may expel the medication from the nose.
8. The nasal route of delivery is not applicable to all drugs. Absorption of polar drugs and some macromolecules are insufficient due to poor membrane permeability, rapid clearance, and enzymatic degradation into the nasal cavity.
9. Although sporadic dosage is unlikely to damage epithelium and/or cilia, chronic applications may lead to more serious toxicity issues and may ultimately damage the cilia and compromise body’s defenses.