The absorptive capacity of the nasal mucosa has been known for centuries. Even if unexploited by pharmaceutical scientists, the abuse of cocaine (including by primitive peoples), and nicotine (snuff) has routinely used this route of administration for systemic delivery. Vast annual tonnages of anti-allergy and decongestant drugs are now administered to the noses of the developed world. These are intended to treat local symptoms, and avoidance of systemic absorption is a favourable feature. a-Adrenergic agonists, antihistamines, and steroids probably lead the list for this topical route of administration.

Therapeutically, interest in the nasal mucosa for systemic absorption of drugs initially centered on its capability to absorb small to moderately sized polypeptides. For example, vasopressin-like drugs (nonapeptides) may be used to treat diabetes insi-pidus in patients with panhypopituitarism. This avoids repeated parenteral injections, and avoids the digestive capacity of the gut.

In the USA, the FDA has issued a draft guideline on establishing the bioequivalence of nasal sprays and aerosols for local absorption. This intent of this guideline is to facilitate the development of generic products for use by this route of administration. This guideline has been challenged on several scientific and technical grounds (e.g. Harrison 2000). While this situation is not yet resolved, many guidelines in the USA remain in draft status for long periods of time, and are treated as definitive.

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