title: Transdermal iontophoresis of rotigotine across human stratum corneum in vitro: influence of pH and NaCl concentration.
abstract: OBJECTIVE
  The aim of this study was to characterize the influence of pH and NaCl concentration on the transdermal iontophoretic transport of the dopamine receptor agonist rotigotine across human stratum corneum (HSC).
  
  
  METHODS
  Rotigotine transport was studied in vitro in side by side diffusion cells according to the following protocol: 6 h of passive diffusion, 9 h of iontophoresis, and 5 h of passive diffusion. A current density of 0.5 mA cm(-2) was used. The influence of donor phase pH (4, 5, and 6) and different concentrations of NaCl (0.07 and 0.14 M) on rotigotine iontophoretic flux were examined. The acceptor phase was phosphate-buffered saline (PBS) at pH 7.4 except in one series of experiments aimed to study the effects of rotigotine solubility on its iontophoretic transport. In this study, PBS at pH 6.2 was used. In separate studies. 14C-mannitol was used as a marker to determine the role of electro-osmosis during iontophoresis.
  
  
  RESULTS
  The estimated iontophoretic steady-state flux (Flux(ss)) of rotigotine was influenced by the pH of the donor solution. At a drug donor concentration of 0.5 mg ml(-1), the iontophoretic flux was 30.0 +/- 4.2 nmol cm(-2) h(-1) at pH 6 vs. 22.7 +/- 5.5 nmol cm(-2) h(-1) at pH 5. However, when the donor concentration was increased to 1.4 mg ml(-1), no significant difference in iontophoretic rotigotine transport was observed between pH 5 and 6. Increase of NaCl concentration from 0.07 M to 0.14 M resulted in a decrease of the rotigotine Flux(ss) from 22.7 +/- 5.5 nmol cm(-2) h(-1) to 14.1 +/- 4.9 nmol cm(-2) h(-1). The contribution of electro-osmosis was estimated less than 17%. Probably due to the lipophilic character of the drug, impeding the partitioning of rotigotine from HSC to the acceptor compartment, steady-state transport was not achieved during 9 h of iontophoresis.
  
  
  CONCLUSIONS
  Both pH and NaCl concentration of the donor phase are crucial on the iontophoretic transport of rotigotine. Electro-repulsion is the main mechanism of the iontophoretic transport of rotigotine.
authors.affiliation: Division of Drug Delivery Technology, Leiden/Amsterdam Center for Drug Research, 2300 RA Leiden, The Netherlands.
authors.forename: Akhmad Kharis
authors.initials: AK
authors.lastname: Nugroho
authors.forename: Gai Ling
authors.initials: GL
authors.lastname: Li
authors.forename: Meindert
authors.initials: M
authors.lastname: Danhof
authors.forename: Joke A
authors.initials: JA
authors.lastname: Bouwstra
mesh_terms: D000279:Administration, Cutaneous; D000465:Algorithms; D000978:Antiparkinson Agents / Q000008:administration & dosage* / Q000493:pharmacokinetics; D002851:Chromatography, High Pressure Liquid; D018491:Dopamine Agonists / Q000008:administration & dosage* / Q000493:pharmacokinetics*; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007478:Iontophoresis; D007700:Kinetics; D009995:Osmosis; D012869:Skin Absorption / Q000502:physiology*; D012965:Sodium Chloride / Q000494:pharmacology; D012995:Solubility; D013764:Tetrahydronaphthalenes / Q000008:administration & dosage* / Q000493:pharmacokinetics; D013876:Thiophenes / Q000008:administration & dosage* / Q000493:pharmacokinetics
chemical_list: D000978:Antiparkinson Agents; D018491:Dopamine Agonists; D013764:Tetrahydronaphthalenes; D013876:Thiophenes; D012965:Sodium Chloride; C047508:rotigotine