title: Tretinoin photostability: comparison of micronized tretinoin (0.05%) gel and tretinoin (0.025%) gel following exposure to ultraviolet a light.
abstract: BACKGROUND
  Various formulations of tretinoin (gel, liquid, cream) have been reported to be unstable on the skin under bright artificial light or sunlight. This photodegradation can potentially influence treatment regimens and possibly modify efficacy. The maximum light energy absorption of tretinoin is in the ultraviolet A region.
  
  
  OBJECTIVE
  To compare the photostability of a micronized formulation of tretinoin (0.05%) aqueos gel with tretinoin (0.025%) gel following exposure to ultraviolet A light for eight hours.
  
  
  METHODS
  Micronized tretinoin (0.05%) gel and tretinoin (0.025%) gel were then exposed to ultraviolet A light with an integrated intensity from 315 to 400nm of 22watt/m(2). Samples of both products were prepared and analyzed for tretinoin and its degradation products using a high-performance liquid chromatography method. Additional duplicate samples were similarly prepared and analyzed after 2,4,6, and 8 hours.
  
  
  RESULTS
  There was a nine-percent degradation of micronized tretinoin in the 0.05% aqueous gel compared to 72-percent degradation of tretinoin in the 0.025% gel following eight-hour ultraviolet A light exposure. The small increase in tretinoin degradation products with micronized tretinoin (0.05%) aqueous gel remained below six percent of the labeled concentration compared to a marked increase in tretinoin degradation products with tretinoin 0.025% gel at two hours that increased to over 66-percent labeled concentration at eight hours.
  
  
  CONCLUSIONS
  Micronized tretinoin (0.05%) aqueous gel showed less than 10-percent degradation when exposed to eight hours of ultraviolet A light, while tretinoin (0.025%) gel showed significant tretinoin degradation.
authors.forename: James Q
authors.initials: JQ
authors.lastname: Del Rosso
authors.forename: Julie
authors.initials: J
authors.lastname: Harper
authors.forename: Radhakrishnan
authors.initials: R
authors.lastname: Pillai
authors.forename: Robert
authors.initials: R
authors.lastname: Moore