The permeability of human eyelid skin to topically applied lidocaine
Cook, Michael T.
This work investigated the permeability of lidocaine across human eyelid skin and compared this with published data for abdominal skin to understand the characteristics of this type of skin and whether topical anaesthesia for eyelid surgery may be feasible. Eyelid skin is thought to have a relatively high permeability to drugs, however how this compares to other body sites has not been previously quantified. Lidocaine solutions at pH 7.0 and 5.5 were applied to human eyelid skin mounted in Franz diffusion cells. Anatomical features of eyelid skin that may be linked to its increased permeability, superficial corneocyte area and stratum corneum (SC) thickness were measured using light microscopy. Steady-state fluxes of lidocaine at pH 7.0 and pH 5.5 were 283.9 and 41.0 μg/cm2/hr, 2.4 and 3.2 times greater respectively than literature values for abdominal skin. Superficial eyelid corneocyte area (800.5 μm2) was 35% smaller and the eyelid SC thickness (14.9 μm) was 31% thinner than reported abdominal skin values. These suggest that a shorter diffusional pathlength across the eyelid SC contributes to increased lidocaine permeability. The relatively high permeability of eyelid skin to lidocaine indicates considerable potential for achieving strong topical anaesthetic effects at this site.