Schema of a transdermal drug delivery system. Transdermal drug delivery systems involve a backing to protect the patch from the environment, a drug reservoir, a porous membrane that limits the rate of drug transfer, and an adhesive to secure the patch to the skin surface at the stratum corneum epidermidis. Drug uptake is then determined by additional factors such as skin thickness and blood flow in the skin (see text for details). Reproduced with permission from Varvel et al.Anesthesiology. 1989;70:933.
Anatomy of the nasal mucosa-cribriform plate interface. The nasal mucosa is the only location in the body that provides a direct connection between the central nervous system and the atmosphere. Drugs administered to the nasal mucosa rapidly traverse through the cribriform plate into the central nervous system by three routes: (1) directly by the olfactory neurons, (2) through supporting cells and the surrounding capillary bed, and (3) directly into the cerebrospinal fluid. Reproduced with permission from Hilger PA. Fundamentals of Otolaryngology, A Textbook of Ear, Nose and Throat Diseases. 6th ed. Philadelphia, PA: WB Saunders Co; 1989:184.