Electrorepulsion versus electroosmosis: Effect of pH on the iontophoretic flux of 5-fluorouracil

Virginia Merino, Alicia López, Yogeshvar N. Kalia, Richard H. Guy

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72 Citations (SciVal)


Purpose. To delineate the contributions of electrorepulsion and electroosmosis to the iontophoretic flux of 5-FU across porcine skin in vitro. Also, the isoelectric point (pI) of the skin model was determined. Methods. The electrotransport of 5-FU, anode-to-cathode ('anodal') and cathode-to-anode ('cathodal') was determined as a function of the pH of the electrolyte bathing the skin. Results. At pH 8.5, the drug (pK(a) ~8) is negatively charged and 'cathodal', viz. electrorepulsive, transport is much greater than that in the opposite direction. At pH 7.4, where ~25% of 5-FU is charged, electrorepulsive and electroosmotic ('anodal') fluxes are balanced. Decreasing the pH to 6, and then 5, reduces the percentage of ionized 5-FU such that 'anodal' electroosmosis dominates across the negatively-charged membrane. But, at pH 4, 'anodal' and 'cathodal' fluxes are again equal suggesting neutralization of the skin (i.e., pI ~ 4). This is confirmed at pH 3, where 'cathodal' electroosmosis dominates across the now net-positively charged barrier. Conclusions. Electrotransport is sensitive, mechanistically, to the properties of the permeant and of the skin; interactions of, for example, the drug or constituents of a formulation, that alter the barrier's net charge, can affect iontophoretic delivery. The pI of porcine ear skin is ~4.

Original languageEnglish
Pages (from-to)758-761
Number of pages4
JournalPharmaceutical Research
Issue number5
Publication statusPublished - 30 May 1999


  • 5- fluorouracil
  • Electroosmosis
  • Iontophoresis
  • Isoelectric point
  • Percutaneous absorption

ASJC Scopus subject areas

  • Biotechnology
  • Molecular Medicine
  • Pharmacology
  • Pharmaceutical Science
  • Organic Chemistry
  • Pharmacology (medical)


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