Effects of intramuscular administration of low doses of medetomidine and medetomidine-butorphanol in middle-aged and old dogs

Objective-To determine effects of low doses of medetomidine administered wi th and without butorphanol and glycopyrrolate to middle-aged and old dogs. Design-Prospective randomized clinical trial. Animals-88 healthy dogs greater than or equal to 5 years old. Procedure-Dogs were assigned randomly to receive medetomidine (2, 5, or 10 mu g/kg [0.9, 2.3, or 4.6 mu g/lb] of body weight, IM) alone or with glycop yrrolate (0.01 mg/kg [0.005 mg/lb], SC), medetomidine (10 mu g/kg) and buto rphanol (0.2 mg/kg [0.1 mg/lb], IM), or medetomidine (10 mu g/kg), butorpha nol (0.2 mg/kg), and glycopyrrolate (0.01 mg/kg). Anesthesia was induced wi th thiopental sodium and maintained with isoflurane. Degree of sedation and analgesia were determined before and after medetomidine administration. Re spiratory rate, heart rate, and mean arterial blood pressure were determine d 10 and 30 minutes after medetomidine administration. Adverse effects and amounts of thiopental and isoflurane used were recorded. Results-Sedation increased after medetomidine administration in 79 of 88 do gs, but decreased in 7 dogs that received 2 or 5 mu g of medetomidine/kg. M ean postsedation analgesia score and amounts of thiopental and isoflurane u sed were less in dogs that received medetomidine and butorphanol, compared with other groups. Respiratory rate, heart rate, and blood pressure were no t different among groups. Significantly more adverse effects developed in d ogs that did not receive glycopyrrolate. Conclusions and Clinical Relevance-Administration of medetomidine (10 mu g/ kg, IM) and butorphanol (0.2 mg/kg, IM) induced sedation and analgesia and reduced amounts of thiopental and isoflurane required for anesthesia in mid dle-aged and old dogs. Glycopyrrolate decreased frequency of medetomidine-a ssociated adverse effects.