title: Assessment of the lateral diffusion and penetration of topically applied drugs in humans using a novel concentric tape stripping design.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University, Melbourne, Victoria, Australia.
authors.forename: C M
authors.initials: CM
authors.lastname: Gee
authors.forename: J A
authors.initials: JA
authors.lastname: Nicolazzo
authors.forename: A C
authors.initials: AC
authors.lastname: Watkinson
authors.forename: B C
authors.initials: BC
authors.lastname: Finnin
mesh_terms: D000269:Adhesives / Q000737:chemistry; D000287:Administration, Topical; D000328:Adult; D018712:Analgesics, Non-Narcotic / Q000008:administration & dosage* / Q000493:pharmacokinetics; D000893:Anti-Inflammatory Agents / Q000008:administration & dosage* / Q000493:pharmacokinetics; D002110:Caffeine / Q000008:administration & dosage* / Q000493:pharmacokinetics; D000697:Central Nervous System Stimulants / Q000008:administration & dosage* / Q000493:pharmacokinetics; D016503:Drug Delivery Systems / Q000295:instrumentation*; D004817:Epidermis / Q000378:metabolism*; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000008:administration & dosage* / Q000493:pharmacokinetics; D007052:Ibuprofen / Q000008:administration & dosage* / Q000493:pharmacokinetics; D008297:Male; D012869:Skin Absorption; D055815:Young Adult
chemical_list: D000269:Adhesives; D018712:Analgesics, Non-Narcotic; D000893:Anti-Inflammatory Agents; D000697:Central Nervous System Stimulants; D002110:Caffeine; D006854:Hydrocortisone; D007052:Ibuprofen