title: Influence of drug concentration on the diffusion parameters of caffeine.
abstract: OBJECTIVE
  In the fields of the pharmaceutical and cosmetic industries and in toxicology, the study of the skin penetration of molecules is very interesting. Various studies have considered the impact of different physicochemical drug characteristics, skin thickness, and formulations, on the transition from the surface of the skin to the underlying tissues or to the systemic circulation; however, the influence of drug concentration on the permeation flux of molecules has rarely been raised. Our study aims to discover the influence of caffeine concentration in a formulation on the percutaneous penetration from gels, as a result of different dose applications to polysulfate membrane and human skin.
  
  
  METHODS
  For this purpose, three identical base gels were used at 1, 3, and 5% of caffeine, to evaluate the effect of the concentration of caffeine on in vitro release through the synthetic membrane and ex vivo permeation through the human skin, using diffusion Franz(TM) cells.
  
  
  RESULTS
  The diffusion through the epidermal tissue was significantly slower than through the synthetic membrane, which recorded an increase of flux with an increase in the concentration of caffeine. The skin permeation study showed that diffusion depended not only on the concentration, but also on the deposited amount of gel. Nevertheless, for the same amount of caffeine applied, the flux was more significant from the less concentrated gel.
  
  
  CONCLUSIONS
  Among all the different concentrations of caffeine examined, 1% gel of caffeine applied at 5 mg / cm(2) showed the highest absorption characteristics across human skin.
authors.affiliation: Laboratory of Skin Pharmacology and Cosmetology, School of Pharmacy, Paris-Sud University, 5, Jean Baptiste Clément street, 92296, Chatenay-Malabry, France.
authors.forename: R Ben
authors.initials: RB
authors.lastname: Mustapha
authors.forename: C
authors.initials: C
authors.lastname: Lafforgue
authors.forename: N
authors.initials: N
authors.lastname: Fenina
authors.forename: J P
authors.initials: JP
authors.lastname: Marty