title: Effect of ionization and vehicle on skin absorption and penetration of azelaic acid.
abstract: OBJECTIVE
  The aim of this study is to investigate the effect of ionization and vehicle of topical formulations on skin absorption and penetration of azelaic acid (AZA).
  
  
  METHODS
  In vitro transport of AZA was determined for two topical formulations containing AZA with pH values of 3.9 and 4.9, respectively. FINACEA(®) (15% AZA gel), a US Food and Drug Administration approved drug for treatment of acne and rosacea, was also used for comparison. Release profile and flux of AZA were determined in an in vitro hairless mouse skin model using Franz Diffusion Cell.
  
  
  RESULTS
  The data have shown that a higher concentration of AZA is retained in the epidermis/dermis layer and the whole skin for the formulation with pH = 4.9 as compared to that with pH = 3.9 at an active loading level of 2.82 mg/cm(2). In addition, the flux of ionized species of AZA in the pH 4.9 formulation (128.4 ± 35.9 μg/cm(2)/h) is approximately five-fold greater than that in the pH 3.9 formulation (27.7 ± 4.0 μg/cm(2)/h). The results suggest that the ionized AZA penetrates through the skin and accounts for majority of the total flux.
  
  
  CONCLUSIONS
  This study has demonstrated that the penetration and absorption of AZA show a strong pH- and vehicle-dependency. Solubilization is the rate-limiting step in percutaneous absorption of AZA.
authors: Tianjin Key Laboratory of Drug Delivery & High-Efficiency, School of Pharmaceutical Science and Technology, Tianjin University, PR China.
authors: Nan
authors: N
authors: Li
authors: Xiaohong
authors: X
authors: Wu
authors: Weibu
authors: W
authors: Jia
authors: Michelle C
authors: MC
authors: Zhang
authors: Fengping
authors: F
authors: Tan
authors: Jerry
authors: J
authors: Zhang
mesh_terms: D000279:Administration, Cutaneous; D000818:Animals; D002626:Chemistry, Pharmaceutical / Q000379:methods; D020405:Dermis / Q000187:drug effects / Q000378:metabolism*; D003998:Dicarboxylic Acids / Q000737:chemistry* / Q000493:pharmacokinetics*; D004817:Epidermis / Q000187:drug effects / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008297:Male; D051379:Mice; D008812:Mice, Hairless; D014677:Pharmaceutical Vehicles / Q000737:chemistry* / Q000494:pharmacology*; D012869:Skin Absorption / Q000187:drug effects*
chemical_list: D003998:Dicarboxylic Acids; D014677:Pharmaceutical Vehicles; C010038:azelaic acid