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Ninety cats scheduled to undergo surgical procedures requiring the provision of postoperative analgesia were premedicated with either 0·1, 0·3 or 0·5 mgl/kg of racemic methadone by intramuscular injection. Each cat was assessed on three behavioural criteria before administration and again 20 minutes later. In a further 20 cats a specific assessment was made of the respiratory rate, heart rate and intraoperative minute volume during ovariohysterectomy following premedication with methadone (0·5 mgl/kg intramuscularly). In these cats an assessment of duration of analgesia was attempted. There was no significant change in behavioural scores following premedication with methadone. No cat vomited or became excited. No evidence of serious respiratory depression was found in the 20 cats monitored in detail. Duration of analgesia in cats receiving methadone (0·5 mgl/kg intramuscularly) before ovariohysterectomy varied from 1·5 to over 6·5 hours. Methadone may be used at dose rates of up to 0·5 mg/kg as a premedicant for cats without significant risk of undesirable behavioural changes or serious intraoperative respiratory depression when combined with the anaesthetic protocol described.

Fifteen cats had anaesthesia induced by intramuscular injection of medetomidine combined with ketamine. By five minutes after drug administration, heart rate had decreased by 31 per cent, respiratory rate had decreased by 70 per cent and systolic blood pressure had increased by 69 per cent. Atipamezole administration was associated with a decrease in systolic blood pressure and an increase in heart and respiratory rates. Time to first head lift was eight minutes and to sternal recumbency 12 minutes after atipamezole administration. Postoperative analgesia was provided by methadone, administered when the cats adopted sternal recumbency.

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