title: A study on the influence of emulsion droplet size on the skin penetration of tetracaine.
abstract: OBJECTIVE
  The influence of emulsion droplet size on the skin penetration of a model drug, tetracaine, was studied. For this purpose, in vitro dermal and transdermal delivery of tetracaine from 6 emulsions (3 macro-emulsions with droplet sizes >1 microm and 3 nano-emulsions with droplet sizes <100 nm) were tested.
  
  
  METHODS
  Two approaches were used: in the first one, the composition of the emulsions was kept constant, while in the second one, the surfactant concentration in the aqueous phase was kept constant by varying the overall surfactant concentration.
  
  
  RESULTS
  The results from emulsions differing only in droplet size did not provide statistically significant evidence for the anticipated increase in transdermal or dermal delivery (after 24 h) when reducing emulsion droplet size. The same results were obtained when the surfactant concentration in the aqueous phase was kept constant, indicating that there is no influence of emulsion droplet size on the skin penetration of tetracaine within the droplet size range studied.
  
  
  CONCLUSIONS
  This is in contrast to what has been reported in various publications that claim penetration to increase with reducing droplet size. It should be noted that the results reported so far are based on emulsions that apart from droplet size also differed in composition and/or system components.
authors.affiliation: Departament de Tecnologia de Tensioactius, Institut d'Investigacions Químiques i Ambientals de Barcelona, CSIC, Barcelona, Spain.
authors.forename: P
authors.initials: P
authors.lastname: Izquierdo
authors.forename: J W
authors.initials: JW
authors.lastname: Wiechers
authors.forename: E
authors.initials: E
authors.lastname: Escribano
authors.forename: M J
authors.initials: MJ
authors.lastname: García-Celma
authors.forename: T F
authors.initials: TF
authors.lastname: Tadros
authors.forename: J
authors.initials: J
authors.lastname: Esquena
authors.forename: J C
authors.initials: JC
authors.lastname: Dederen
authors.forename: C
authors.initials: C
authors.lastname: Solans
mesh_terms: D000287:Administration, Topical; D000779:Anesthetics, Local / Q000008:administration & dosage* / Q000737:chemistry / Q000493:pharmacokinetics*; D016503:Drug Delivery Systems; D004655:Emulsions; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D010316:Particle Size; D012867:Skin / Q000378:metabolism*; D012869:Skin Absorption; D013499:Surface Properties; D013501:Surface-Active Agents; D013748:Tetracaine / Q000008:administration & dosage* / Q000737:chemistry / Q000493:pharmacokinetics*
chemical_list: D000779:Anesthetics, Local; D004655:Emulsions; D013501:Surface-Active Agents; D013748:Tetracaine