The purpose of this study was to investigate the cardiopulmonary, sedative, and analgesic effects of 4 intravenous dose levels (50ug/kg, 100ug/kg, 150ug/kg, and 200ug/kg) of medetomidine (med), a potent, specific, and selective alpha-2-agonist, in rhesus macaques. 15 Mature, healthy, chair-trained macaques each underwent 4 randomized, blinded trials, 1 trial for each dose level. Mean arterial, systolic, and diastolic pressure, heart rate, electrocardiography readout (lead II), o2 saturation, respiratory rate, and rectal temperature were monitored continuously while the monkey was in a standard chair-restraint device. Depth of sedation/analgesia was evaluated by scoring the following parameters; mental state, posture, bite reflex, ocular signs, and response to pain (finger pinch), manual manipulation, and noise. All 4 dose levels produced marked bradycardia and hypotension. While no statistical difference existed between the 100ug/kg, 150ug/kg, and 200ug/kg doses, the duration and depth of the cardiovascular effects were significantly shorter and less pronounced in the 50ug/kg trials. 10 Monkeys experienced periods of sinus arrest immediately after drug administration. This effect was independent of dose and generally resolved within 5 minutes. Med sedation was characterized by mild to marked stupor and profound muscle relaxation. While the plane of sedation/analgesia produced by med at 100-200ug/kg was suitable for physical exams and minorly invasive procedures, the plane produced by the 50ug/kg dose was not sufficient to safely perform any veterinary procedures. Despite the profound bradycardia and hypotension produced by med, the drug can be used safely as a sedative/analgesic agent in rhesus macaques with proper patient monitoring. Future studies investigating the combination of med with the cardiosupportive drug ketamine must be performed before med gains wide acceptance in nonhuman primate medicine.
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