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Transport of Azithromycin into Extravascular Space in Rats

Shinji Kobuchi1, Miki Aoki1, Chiaki Inoue1

  • 1Department of Pharmacokinetics, Kyoto Pharmaceutical University, Kyoto, Japan.

Antimicrobial Agents and Chemotherapy
|September 8, 2016
PubMed

Insights

Azithromycin (an antibiotic) stays in skin interstitial fluid longer than expected, reaching high levels that may fight infections. This prolonged presence suggests trapped drug within cells, enhancing its long-lasting effects at infection sites.

Area of Science:

  • Pharmacology
  • Dermatology
  • Microbiology

Background:

  • Azithromycin (an antibiotic) exhibits prolonged retention in soft tissue interstitial fluid, with unbound concentrations noted in clinical trials.
  • Previous studies utilized microdialysis to measure unbound azithromycin concentrations in interstitial fluid.

Purpose of the Study:

  • To quantify total azithromycin concentrations in rat skin interstitial fluid using a novel microneedle array method.
  • To investigate the disposition and retention kinetics of azithromycin in skin interstitial fluid.

Main Methods:

  • Utilized dissolving microneedle arrays to collect interstitial fluid directly from rat skin.
  • Measured total azithromycin concentrations in skin interstitial fluid and plasma over time.
  • Calculated skin/plasma concentration ratios.

Main Results:

  • Total azithromycin concentrations in skin interstitial fluid were 4-5 times higher than plasma concentrations.
  • A stasis of azithromycin concentration in interstitial fluid was observed at low plasma levels.
  • The skin/plasma concentration ratio increased significantly post-dosing (4.3 to 83.1).

Conclusions:

  • Azithromycin appears to be trapped within white blood cells and phagocytic cells in both blood and interstitial fluid.
  • This cellular trapping leads to high total azithromycin concentrations and prolonged retention in skin.
  • The sustained high concentrations in skin interstitial fluid suggest long-lasting antimicrobial effects at infection sites, exceeding the minimum inhibitory concentration (MIC).

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