2003 Volume 63 Issue 1 Pages 34-45
Recent studies have focused on the hair follicle as a potential pathway for both localized and systemic drug delivery. When drug penetration through human scalp skin was investigated using liquid formulations containing lipophilic and hydrophilic drugs in vitro, lipophilic melatonin (MT) and ketoprofen (KP) showed high permeabilities through scalp skin. Absorption enhancers, N-methyl-2-pyrrolidone and isopropylmyristate, only slightly increased the fluxes. Hydrophilic fluorouracil (5FU) and acyclovir (ACV) also penetrated across the skin with relatively large fluxes. However, there was large variability in the fluxes of drugs across scalp skins. There was a correlation between the flux and hair follicle density (r=0.651 for MT and r=0.666 for ACV). Fluorescent probes, nile red and sodium fluorescein, permeated into the junction of the internal and external root sheath of follicles and diffused into the dermis via the outer root sheath at the initial times. The penetration of MT and 5FU through scalp skin was much higher (37 and 48 times, respectively) than that via human abdominal skin. It has been demonstrated that topically-applied liposomes and microspheres are efficient in specifically targeting the delivery of a wide variety of compounds into the hair follicles. Additionally, hair follicles were a significant pathway for electroosmotic solution flow during iontophoresis. This review indicates a basis that drug delivery through human scalp skin will offer an available delivery means for many lipophilic and hydrophilic drugs.
