Purpose: To determine the extent of lateral spread and stratum corneum (SC) penetration of caffeine (CAF), hydrocortisone (HC) and ibuprofen (IBU) using a novel concentric tape stripping technique.
Method: Ethanolic solutions of CAF, HC or IBU were applied to the forearm of 8 volunteers. At various time points, 10 successive layers of SC were removed by stripping with tapes perforated into concentric rings and analysed for drug concentration and mass of SC protein. In vitro permeation studies assessed the percutaneous absorption of these compounds across human skin.
Results: CAF and IBU showed significant lateral spreading across the SC while HC formed a drug depot at the site of application. Relative to the applied dose, the in vivo recovery of all compounds from the combined 10 strips at 3 mins ranged between 83.0 and 92.9 % and decreased to between 64.5 and 66.9 % at 3 h. IBU recovery further decreased to 47.7 ± 5.6 % at 6 h, correlating with greater in vitro penetration relative to CAF and HC.
Conclusion: Drug concentration decreased with increased lateral distance from the application site. The lower recovery of IBU in the upper tape strip regions compared to CAF and HC may be a consequence of greater penetration into the SC with time.