CLINICAL COMPARISON OF MEDETOMIDINE WITH XYLAZINE L-METHADONE IN DOGS

Seventy-two healthy dogs required sedation and analgesia for a variety of procedures causing discomfort or pain, They were treated either wi th the alpha(2)-agonist medetomidine at 40 mu g/kg (15 intravenously a nd 17 intramuscularly), or 80 mu g/kg (15 intravenously and 15 intramu scularly) or with xylazine plus 1-methadone (1.0 mg) (10 intravenously ), The levels of sedation, analgesia and safety were compared clinical ly and by measurements of the effects on the electrocardiogram (ECG) a nd blood gases, body temperature, haematology and clinical chemistry, Sedation was achieved reliably with both medetomidine and xylazine plu s I-methadone but its onset, depth and duration were influenced by the dose and route of administration, In the medetomidine-treated dogs, i ntravenous administration resulted in more rapid sedation and the effe cts of the higher dose were deeper and longer lasting, The small dogs receiving 40 mu g/kg may have been underdosed. The initial analgesic e ffects in response to a pin prick to the body surface were sufficient and similar for both drugs, except for the intramuscular dose of 40 mu g/kg medetomidine. Analgesia for the clinical procedures was less rel iable with medetomidine and was not always adequate even at the high d ose, but xylazine plus 1-methadone assured analgesia in almost every c ase, Medetomidine resulted in marked bradycardia, lasting as long as t he sedation and the ECG revealed a sinus arrhythmia with sinoatrial an d atrioventricular blocks grade I and II as a sign of interference wit h transduction, The bradycardia with xylazine plus 1-methadone was les s pronounced. A decrease in respiratory rate accompanying sedation had no influence on blood gases and blood acidity in the dogs treated wit h medetomidine but caused a respiratory acidosis with xylazine plus I- methadone, Body temperature decreased with all treatments for the dura tion of the period of sedation, Blood glucose concentration increased to a similar extent in all treatment groups, but all other haematologi cal and clinicochemical variables remained unchanged, Treatment with t he specific alpha(2) antagonist, atipamezole, reversed the sedation an d cardiovascular and pulmonary effects due to medetomidine within minu tes.