Effects of medetomidine, L-methadone, and their combination on arterial blood gases in dogs.
OBJECTIVE
To investigate the influence of L-methadone on medetomidine-induced changes in arterial blood gases and clinical sedation in dogs.


METHODS
Prospective experimental cross-over study (Latin square design).


METHODS
Five 1-year-old purpose bred laboratory beagle dogs of both sexes.


METHODS
Each dog was treated three times: medetomidine (20 microg kg(-1) IV), L-methadone (0.1 mg kg(-1) IV) and their combination. Arterial blood was collected for blood gas analysis. Heart and respiratory rates were recorded, and clinical sedation and reaction to a painful stimulus were scored before drug administration and at various time points for 30 minutes thereafter.


RESULTS
Arterial partial pressure of oxygen decreased slightly after medetomidine administration and further after medetomidine/L-methadone administration (range 55.2-86.7 mmHg, 7.4-11.6 kPa, at 5 minutes). A slight increase was detected in arterial partial pressure of carbon dioxide after administration of l-methadone and medetomidine/L-methadone (42.6 +/- 2.9 and 44.7 +/- 2.4 mmHg, 5.7 +/- 0.4 and 6.0 +/- 0.3 kPa, 30 minutes after drug administration, respectively). Arterial pH decreased slightly after administration of L-methadone and medetomidine/L-methadone. Heart and respiratory rates decreased after administration of medetomidine and medetomidine/L-methadone, and no differences were detected between the two treatments. Most dogs panted after administration of L-methadone and there was slight sedation. Medetomidine induced moderate or deep sedation, and all dogs were deeply sedated after administration of medetomidine/L-methadone. Reaction to a noxious stimulus was strong or moderate after administration of methadone, moderate or absent after administration of medetomidine, and absent after administration of medetomidine/L-methadone.


CONCLUSIONS
At the doses used in this study, L-methadone potentiated the sedative and analgesic effects and the decrease in arterial oxygenation induced by medetomidine in dogs, which limits the clinical use of this combination.
Raekallio
Marja R
MR
Department of Equine and Small Animal Medicine, Faculty of Veterinary Medicine, University of Helsinki, Helsinki, Finland. marja.raekallio@helsinki.fi
Räihä
Maija P
MP
Alanen
Maarit H
MH
Sarén
Nina M
NM
Tuovio
Tove A
TA
D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001784:Blood Gas Analysis / Q000662:veterinary; D018592:Cross-Over Studies; D004285:Dogs / Q000097:blood*; D004359:Drug Therapy, Combination; D005260:Female; D006993:Hypnotics and Sedatives / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D020926:Medetomidine / Q000008:administration & dosage / Q000494:pharmacology*; D008691:Methadone / Q000008:administration & dosage / Q000494:pharmacology*; D010865:Pilot Projects
D000701:Analgesics, Opioid; D006993:Hypnotics and Sedatives; D020926:Medetomidine; D008691:Methadone