Effects of morphine, butorphanol, buprenorphine, and U50488H on the minimum alveolar concentration of isoflurane in cats.
OBJECTIVE
To determine whether opioids with varying interactions at receptors induce a reduction in minimum alveolar concentration (MAC) of isoflurane in cats.


METHODS
12 healthy, female, spayed cats.


METHODS
Cats were anesthetized with isoflurane and instrumented to allow collection of arterial blood and measurement of arterial blood pressure. Each drug was studied separately, and for each drug cats were randomly allocated to receive 2 doses. The drugs studied were morphine (0.1 or 1.0 mg/kg), butorphanol (0.08 or 0.8 mg/kg), buprenorphine (0.005 and 0.05 mg/kg), and U50488H (0.02 and 0.2 mg/kg). All drugs were diluted in 5 ml of saline (0.9% NaCl) solution and infused IV for 5 minutes. The MAC of isoflurane was determined in triplicate, the drug administered, and the MAC of isoflurane redetermined for a period of 3 hours.


RESULTS
All drugs had a significant effect on MAC over time. With morphine only, the effect on MAC over time was different between doses. The greatest mean (+/- SD) reductions in MAC of isoflurane in response to morphine, butorphanol, buprenorphine, and U50488H administration were 28 +/- 9, 19 +/- 3, 14 +/- 7, and 11 +/- 7%, respectively.


CONCLUSIONS
Morphine (1.0 mg/kg) and butorphanol (0.08 and 0.8 mg/kg) induced significant reductions in MAC of isoflurane that were considered clinically important. Although significant, reductions in MAC of isoflurane induced by morphine (0.1 mg/kg), buprenorphine (0.005 and 0.05 mg/kg), and U50488H (0.02 and 0.2 mg/kg) were not considered clinically relevant because they fell within the error of the measurement technique. Administration of morphine or butorphanol decreases the need for potent inhalant anesthetics in cats and could potentially be beneficial in combination with inhalants.
Ilkiw
Jan E
JE
Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis 95616, USA.
Pascoe
Peter J
PJ
Tripp
Linda D
LD
D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer / Q000494:pharmacology*; D018712:Analgesics, Non-Narcotic / Q000494:pharmacology*; D000701:Analgesics, Opioid / Q000494:pharmacology*; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000493:pharmacokinetics*; D000818:Animals; D001784:Blood Gas Analysis / Q000662:veterinary; D001794:Blood Pressure / Q000187:drug effects; D002047:Buprenorphine / Q000494:pharmacology*; D002077:Butorphanol / Q000494:pharmacology*; D002415:Cats / Q000378:metabolism*; D004347:Drug Interactions; D004562:Electrocardiography / Q000662:veterinary; D005260:Female; D007530:Isoflurane / Q000008:administration & dosage / Q000493:pharmacokinetics*; D009020:Morphine / Q000494:pharmacology*; D011650:Pulmonary Alveoli / Q000187:drug effects / Q000378:metabolism; D011897:Random Allocation
D018712:Analgesics, Non-Narcotic; D000701:Analgesics, Opioid; D018685:Anesthetics, Inhalation; D002047:Buprenorphine; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D009020:Morphine; D007530:Isoflurane; D002077:Butorphanol