Analgesia and serum concentrations of extradural, subdural and intraperitoneal fentanyl in a rat model

  • Lynleigh Immelman
  • Sheldon Roth
  • Mary Anne Sabourin
  • Leo Strunin
Reports of Investigation


The effects of epidural, subdural and intraperitoneal fentanyl were determined on the tail flick response of the rat using the response latency as a measure of analgesia. Dose-timeresponse curves were generated for incremental doses of fentanyl administered at constant injection volumes. Serum concentrations at varying doses were determined using a radioimmunoassay technique. It was found that serum concentrations for extradural, subdural and intraperitoneal fentanyl were similar at the low doses, but differed significantly at higher doses suggesting that pharmacokinetic differences may be concentration dependent. Extradural administration of naloxone (0.004 mg) was able to antagonize extradural fentanyl (8.0 μg), a dose eight-fold greater than the lowest maximally effective dose. The relationship between serum fentanyl concentrations and administered doses suggest that the analgesic properties of extradural and subdural fentanyl are in part dependent on centrally mediated actions.

Key words

anaesthetic techniques: epidural, intraperitoneal, spinal analgesia: measurement, rat tail flick response analgesics: fentanyl antagonists, narcotic: naloxone 


Les effets dufentanil administré en épidurale, en sousdurale et intrapéritonéale ont été déterminés chez des rats utilisant le temps de latence comme mesure du degré de l’analgésie. Des courbes de réponse dose-temps ont été créées pour des doses croissantes de fentanyl administrées à des volumes d’injection constants. Les concentrations plasmatiques ont été déterminées par radioimmunoessai. On a trouvé que les concentrations plasmatiques pour l’administration extradurale, sousdurale et intrapéritonéale de fentanyl, étaient similaires à des doses basses mais significativement différentes à des doses élevées suggérant des différences pharmacocinétiques dépendant de la concentration. Ladministration extradurale de naloxone (0,004 mg) antagonisait le fentanyl (8,0 μg) administré par voie extradurale, une dose huit fois plus grande que la plus basse dose efficace. La relation entre les concentrations plasmatiques de fentanyl et les doses administrées suggérent que les propriétés analgésiques de l’administration de fentanyl par voie extradurale et sousdurale était en d’origine centrale.


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Copyright information

© Canadian Anesthesiologists 1990

Authors and Affiliations

  • Lynleigh Immelman
    • 1
  • Sheldon Roth
    • 1
  • Mary Anne Sabourin
    • 1
  • Leo Strunin
    • 1
  1. 1.Department of AnaesthesiaFoothills Hospital at the University of CalgaryCalgaryCanada

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