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ABSTRACT. The epidural distribution of iohexol (0.2 ml/kg) administered at thoracic vertebrae (Thoracic group) and lumbar vertebrae (Lumbar group) was compared by computed tomographic (CT) epidurography in dogs. The total spread of iohexol was similar between the 2 groups upon reaching a similar cranial level. The maximal CT values were higher at the C7/T1 and T4/T5 levels in Thoracic group, but they were higher at the T13/L1 and L4/L5 levels in Lumbar group (P<0.05). This result suggests that the distribution pattern of the drug administered epidurally at thoracic vertebrae and lumbar vertebrae is different in dogs.

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ABSTRACT. Behavioral effects induced by intravenous administration of morphine at 0.3, 0.6, 1.2, and 2.4 g/kg and fentanyl at 5, 10, 20, and 40 g/kg were evaluated in dogs and cats. In dogs, fentanyl and morphine depressed activity and level of consciousness in a dosedependant manner. In cats, higher doses of fentanyl stimulated activity temporarily, but excitement, so-called "opioid mania," was not observed. Morphine induced distinctive behavioral changes characterized by sitting with fixed staring, and "opioid mania" was not observed in cats. Mu-Opioid receptor agonists such as morphine and fentanyl are potent and effective analgesics for severe pain. Therefore, these opioids are widely used in various animal species [13]. However, many veterinarians are reluctant to use opioids in cats because of concerns of secondary excitement and low reliability [3,8,9]. Excitement and aggressive responses induced by high doses of opioids in cats are referred as opioid mania and are some of the most concerning side effects of opioids [1,2,8]. Some veterinarians are afraid that opioid mania may even occur in cats at the doses appropriate for dogs. To avoid these undesirable side effects, lower doses of opioids are usually recommended for cats compared with those recommended in dogs [13]. However, there are few reports about the actual behavioral effects or opioid mania induced by opioids in cats, especially by fentanyl [1,2,6]. In this study, we evaluated the behavioral effects induced by fentanyl and morphine at clinical or supraclinical doses in cats compared with those in dogs.Six healthy beagles and 6 healthy cats were used in this study. They were used repeatedly in a random order. The dogs weighed 11.5 ± 1.9 kg and were 5.6 ± 0.6 years old. The cats weighed 4.3 ± 0.6 kg and were 3.3 ± 0.3 years old. At least 7 days were allowed to pass when using the same animal repeatedly. The same animal was not given the same treatment more than once. Food was withheld for 12 hr before each experiment, but water was freely available. This study was approved by the Animal Care Committee of the Graduate School of Agricultural and Life Sciences at the University of Tokyo. Experiments were performed in a quiet room. After placement of a catheter in the cephalic vein for drug administration and measurement of the baseline heart rate (HR) and respiratory rate (RR), animals were given 1 of the following treatments: (1) saline or (2) morphine (morphine, Daiichi Sankyo Propharma Co., Ltd., Tokyo, Japan) at 0.3, 0.6, 1.2, and 2.4 mg/kg, or (3) fentanyl (fentanyl, Daiichi Sankyo Propharma Co., Ltd.) at 5, 10, 20, and 40 g/kg. The calculated dose of drug was diluted with saline to 0.8 ml/kg. Behavioral effects were assessed by changes in locomotor activity and posture for 120 min after drug administration. Vomiting, changes in pupil size and euphoria were also recorded. The end point of the change in locomotor activity was documented as normal, increased, or decreased. The end point of the change in posture was documented as normal, sternal...