title: Influence of light and temperature on the stability of procaine hydrochloride injection.
abstract: OBJECTIVE
  To study the influence of light and heat on the stability of procaine hydrochloride injection.
  
  
  METHODS
  Accelerated tests upon exposure to light at high temperatures were employed.
  
  
  RESULTS
  In experiments with either isothermal heating or exposure to light at high temperatures, the drug degradation rate obeys first-order kinetics. The total rate constant, ktotal, caused by both light and heat can be divided into two parts: ktotal = kdark + klight, where kdark and klight are the rate constants caused by heat and light, respectively. The klight can be expressed as klight = Alight x E x exp(-Ea,light/RT). Where E is the illuminance of light, Alight is an experimental constant related to light sources, and Ea,light is an experimental constant.
  
  
  CONCLUSIONS
  Because the form of klight is similar to the Arrhenius equation, it is suggested that Ea,light might be the observed activation energy of the rate-determining step of the subsequent processes of the photochemical reaction. This viewpoint is supported by the fact that the Ea,light is independent of light sources.
authors.affiliation: School of Pharmacy, West China Medical Center, University of Sichuan.
authors.forename: Tao
authors.initials: T
authors.lastname: Lin
authors.forename: Xian-cheng
authors.initials: XC
authors.lastname: Zhan
authors.forename: Kai-lan
authors.initials: KL
authors.lastname: Li
authors.forename: Lin-li
authors.initials: LL
authors.lastname: Li
authors.forename: Cheng-rong
authors.initials: CR
authors.lastname: Li
mesh_terms: D004355:Drug Stability; D006358:Hot Temperature; D007267:Injections; D008027:Light; D008433:Mathematics; D011343:Procaine / Q000008:administration & dosage / Q000737:chemistry* / Q000528:radiation effects
chemical_list: D011343:Procaine