Clinical comparison of medetomidine with xylazine/l‐methadone in dogs

Abstract

Seventy-two healthy dogs required sedation and analgesia for a variety of procedures causing discomfort or pain. They were treated either with the alpha 2-agonist medetomidine at 40 micrograms/kg (15 intravenously and 17 intramuscularly), or 80 micrograms/kg (15 intravenously and 15 intramuscularly) or with xylazine plus l-methadone (1.0 mg)(10 intravenously). The levels of sedation, analgesia and safety were compared clinically and by measurements of the effects on the electrocardiogram (ECG) and blood gases, body temperature, haematology and clinical chemistry. Sedation was achieved reliably with both medetomidine and xylazine plus l-methadone but its onset, depth and duration were influenced by the dose and route of administration. In the medetomidine-treated dogs, intravenous administration resulted in more rapid sedation and the effects of the higher dose were deeper and longer lasting. The small dogs receiving 40 micrograms/kg may have been underdosed. The initial analgesic effects in response to a pin prick to the body surface were sufficient and similar for both drugs, except for the intramuscular dose of 40 micrograms/kg medetomidine. Analgesia for the clinical procedures was less reliable with medetomidine and was not always adequate even at the high dose, but xylazine plus l-methadone assured analgesia in almost every case. Medetomidine resulted in marked bradycardia, lasting as long as the sedation and the ECG revealed a sinus arrhythmia with sinoatrial and atrioventricular blocks grade I and II as a sign of interference with transduction. The bradycardia with xylazine plus l-methadone was less pronounced. A decrease in respiratory rate accompanying sedation had no influence on blood gases and blood acidity in the dogs treated with medetomidine but caused a respiratory acidosis with xylazine plus l-methadone. Body temperature decreased with all treatments for the duration of the period of sedation. Blood glucose concentration increased to a similar extent in all treatment groups, but all other haematological and clinicochemical variables remained unchanged. Treatment with the specific alpha 2 antagonist, atipamezole, reversed the sedation and cardiovascular and pulmonary effects due to medetomidine within minutes.

Effects of methadone, alone or in combination with acepromazine or xylazine, on sedation and physiologic values in dogs

“…When methadone was administered in combination with xylazine, none of the dogs panted. These results are in contrast with a previous study in which the authors reported a prevalence of panting of 50% in dogs receiving xylazine plus methadone (Kramer et al. 1996).…”

“…Four out of six dogs receiving xylazine–methadone had no pedal withdrawal reflex at least at one time point during the study compared with none of the dogs receiving xylazine alone. A previous study reported better analgesia in dogs treated with xylazine and methadone than in those treated with medetomidine alone (Kramer et al. 1996).…”

“…2001a). The combination of xylazine with l‐methadone resulted in respiratory acidosis in dogs (Kramer et al. 1996).…”

Continuous infusion in adult females dogs submitted to ovariohysterectomy with midazolam-xylazine and/or medetomidine pre-treated with methotrimeprazine and buprenorphine

“…A shorter anesthetic recovery period occurred in G2 (48 min) as compared to G1 (52 min) and, also with a superior quality. o C what has also been reported for different dissociative anesthesia protocols through continuous infusion 2,3,4 .A greater reduction in body temperature as observed by some authors 5,6,7 is due to the peripheral vasoconstriction and blood central redistribution due to the action of a-2 agonists. This is a controversial effect for a-2 agonists lead to peripheral vasodilatation and heat production reduction.…”

Repeated anaesthesia with isoflurane and xylazine/levomethadone/fenpipramide premedication in female Beagle dogs: Influence on general health and wellbeing

“…For the time of sedation and partly beyond it xylazine causes bradycardia, decreases in body temperature and breathing rate (Rector et al 1996, Ilback & Stalhandske 2003. The effects of a xylazine/levomethadone/fenpipramide combination are comparable with what is described for xylazine alone (Kramer et al 1996). Isoflurane is one of the most widely applied volatile anaesthetics in veterinary medicine and was reported in dogs to cause unwanted effects, such as depression of myocardial contractility, hypoventilation, cerebral vasodilation and triggering of malignant hyperthermia, and that it causes irritation to the respiratory tract (Galloway et al 2004).…”