ABSTRACT
Cutaneous drug delivery offers many advantages over alternative routes of administration with regard to target-specic impact, decreased systemic toxicity, avoidance of rst-pass metabolism, variable dosing schedules, and broadened utility to diverse patient populations. A complicating factor is that the skin has evolved mechanisms to impede exogenous molecules, especially hydrophilic ones, from safe passage. The horny layer of the stratum corneum (the topmost layer of the skin) is tightly bonded to an intercellular lipid matrix, making the passage of therapeutics a serious challenge.1 This strong barrier to molecular activity is quite effective at blocking large molecules, which of course make up the majority of active therapeutics.2 Many substances that could, in theory, be used as topical therapeutics have several disadvantages in that they are (i) weakly or not soluble in water; (ii) degraded or inactivated prior to reaching the appropriate target; and (iii) nonspecically distributed to tissues and organs, resulting in undue adverse side effects and limited efcacy at the target site.
