Intranasal drug delivery to the central nervous system: present status and future outlook

Pharmacological treatment of disorders affecting the central nervous system (CNS) is a complex task. Different parameters may negatively influence effective targeting of the CNS and drug compliance, for example, poor brain-blood barrier (BBB) permeability, patient forgetfulness or neglect, and lack of collaboration between caregivers and patients. Pharmaceutical science is constantly looking for new administration strategies for efficient drug delivery to the CNS that could obviate these problems. Drugs can reach the brain through the skin, nasal cavity and oral cavity, and while effective transport of drugs from skin and nasal cavity to the CNS has been documented, these studies did not stimulate the introduction of a substantial number of new drug formulations to treat CNS disorders. Nasal drug delivery, generally used to administer locally acting molecules, is not common for systemic administration, although the possibility and importance of such systemic administration is suggested by several studies. This paper reviewed different anatomical and pharmaceutical factors related to drug administration through the nasal route, and explored whether nasal delivery of selected CNS drugs could improve their pharmacokinetics and patient compliance. This route offers attractive advantages, and pharmaceutical scientists and anatomists should collaborate to improve CNS drug compliance and to increase the number of compounds that can be administered intranasally.