Phenylpiperidine opioid effects on isoflurane minimum alveolar concentration in cats

Robert J. Brosnan, Bruno H. Pypendop, Scott D. Stanley

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


Different structurally related phenylpiperidine opioids exhibit different isoflurane-sparing effects in cats. Because minimum alveolar concentration (MAC) in cats is affected only by very high plasma concentrations of some phenylpiperidine opioids, we hypothesized these effects are caused by actions on nonopioid receptors. Using a prospective, randomized, crossover design, six cats were anesthetized with isoflurane, intubated, ventilated, and instrumented. Isoflurane MAC was measured in triplicate using a tail-clamp and bracketing technique. A computer-controlled intravenous infusion using prior pharmacokinetic models targeted plasma concentrations of 60 ng/ml fentanyl, 10 ng/ml sufentanil, or 500 ng/ml alfentanil, and isoflurane MAC was measured in duplicate. Next, naltrexone 0.6 mg/kg was administered to cats hourly during the opioid infusion, and isoflurane MAC was measured in duplicate. Blood was collected during MAC determinations to measure opioid concentrations. Responses were analyzed using repeated measures ANOVA with significance at p <.05. Alfentanil and sufentanil decreased isoflurane MAC by 16.4% and 6.4%, respectively, and these effects were completely reversed by naltrexone. Fentanyl had no significant effect on isoflurane MAC. Alfentanil and sufentanil modestly reduce isoflurane MAC via agonist effects on opioid receptors. However, these effects are too small to justify clinical use of phenylpiperidine opioids as single agents to reduce MAC in cats.

Original languageEnglish
Pages (from-to)533-537
Number of pages5
JournalJournal of Veterinary Pharmacology and Therapeutics
Issue number6
StatePublished - Nov 2020

Bibliographical note

Publisher Copyright:
© 2020 John Wiley & Sons Ltd


  • MAC
  • alfentanil
  • feline
  • fentanyl
  • sufentanil

ASJC Scopus subject areas

  • Pharmacology
  • General Veterinary


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