Naltrexone does not affect isoflurane minimum alveolar concentration in cats
Article first published online: 24 DEC 2012
© 2012 The Authors. Veterinary Anaesthesia and Analgesia © 2012 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists
Veterinary Anaesthesia and Analgesia
Volume 40, Issue 2, pages 225–228, March 2013
How to Cite
Brosnan, R. J., Pypendop, B. H., Majewski-Tiedeken, C. R., Shilo-Benjamini, Y. and Ilkiw, J. E. (2013), Naltrexone does not affect isoflurane minimum alveolar concentration in cats. Veterinary Anaesthesia and Analgesia, 40: 225–228. doi: 10.1111/vaa.12004
- Issue published online: 13 FEB 2013
- Article first published online: 24 DEC 2012
- Manuscript Accepted: 23 SEP 2011
- Manuscript Received: 2 MAY 2011
- U.C. Davis Center for Companion Animal Health
- National Institutes of Health. Grant Number: GM092821
- minimum alveolar concentration;
To test whether naltrexone, an opioid receptor antagonist, affects the minimum alveolar concentration (MAC) of isoflurane in cats, a species that is relatively resistant to the general anesthetic sparing effects of most opioids.
Randomized, crossover, placebo-controlled, blinded experimental design.
Six healthy adult cats weighing 4.9 ± 0.7 kg.
The cats were studied twice. In the first study, baseline isoflurane MAC was measured in duplicate. The drug (saline control or 0.6 mg kg−1 naltrexone) was administered IV every 40–60 minutes, and isoflurane MAC was re-measured. In the second study, cats received the second drug treatment using identical methods 2 weeks later.
Isoflurane MAC was 2.03 ± 0.12% and was unchanged from baseline following saline or naltrexone administration.
Conclusion and clinical relevance
Minimum alveolar concentration was unaffected by naltrexone. Because MAC in cats is unaffected by at least some mu-opioid agonists and antagonists, spinal neurons that are directly modulated by mu-opioid receptors in this species cannot be the neuroanatomic sites responsible for immobility from inhaled anesthetics.