title: Novel microemulsion enhancer formulation for simultaneous transdermal delivery of hydrophilic and hydrophobic drugs.
abstract: OBJECTIVE
  Microemulsion (ME) systems allow for the microscopic co-incorporation of aqueous and organic phase liquids. In this study, the phase diagrams of four novel ME systems were characterized.
  
  
  METHODS
  Water and IPM composed the aqueous and organic phases respectively, whereas Tween 80 served as a nonionic surfactant. Transdermal enhancers such as n-methyl pyrrolidone (NMP) and oleyl alcohol were incorporated into all systems without disruption of the stable emulsion.
  
  
  RESULTS
  A comparison of a W/O ME with an O/W ME of the same system for lidocaine delivery indicated that the O/W ME provides significantly greater flux (p < 0.025). The water phase was found to be a crucial component for flux of hydrophobic drugs (lidocaine free base, estradiol) as well as hydrophilic drugs (lidocaine HCl, diltiazem HCl). Furthermore, the simultaneous delivery of both a hydrophilic drug and a hydrophobic drug from the ME system is indistinguishable from either drug alone. Enhancement of drug permeability from the O/W ME system was 17-fold for lidocaine free base, 30-fold for lidocaine HCl, 58-fold for estradiol, and 520-fold for diltiazem HCl.
  
  
  CONCLUSIONS
  The novel microemulsion systems in this study potentially offers many beneficial characteristics for transdermal drug delivery.
authors.affiliation: Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
authors.forename: Philp J
authors.initials: PJ
authors.lastname: Lee
authors.forename: Robert
authors.initials: R
authors.lastname: Langer
authors.forename: V Prasad
authors.initials: VP
authors.lastname: Shastri
mesh_terms: D000279:Administration, Cutaneous; D002626:Chemistry, Pharmaceutical; D016503:Drug Delivery Systems / Q000379:methods*; D004655:Emulsions; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D066298:In Vitro Techniques; D008863:Microspheres; D004364:Pharmaceutical Preparations / Q000008:administration & dosage* / Q000737:chemistry* / Q000378:metabolism
chemical_list: D004655:Emulsions; D004364:Pharmaceutical Preparations