Delivery of Topical Drugs to the Olfactory Cleft.

Olfactory dysfunction affects approximately 20% of the population globally, with incidence increasing over the age of 60. The pathophysiology is complex, not yet fully understood, and depends on many factors, including the underlying cause. Despite this, the present literature on olfaction is limited due to significant heterogeneity in methodological approaches. This has resulted in limited effective treatments available for olfactory dysfunction. Medications for olfactory dysfunction can be administered locally (directly to the olfactory epithelium) or systemically (orally or intravenously). Currently, there are various methods for local drug delivery to the olfactory epithelium (nasal drops, nasal sprays, atomisers, pressured meter-dosed inhalers, rinses, and exhalation delivery systems). The aims of this review are to summarise the different methods of drug delivery to the olfactory cleft, evaluate the current literature to assess which method is the most effective in delivering drugs to the olfactory epithelium, and review the medications currently available to treat olfactory dysfunction topically. Going forward, further research is required to better establish effective methods of drug delivery to the olfactory epithelium to treat smell disorders.