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Recently, a mucosal atomization device (MAD) has been applied in veterinary medicine. In the present study, the maximum volume of nasal atomization without aspiration using MAD was examined in eight healthy female Japanese White (JW) rabbits. Each rabbit had their head and neck examined by computed tomography before and after nasal atomization with four different doses (0.15, 0.3, 0.45, and 0.6 ml per nostril) of diluted contrast medium (1:2 mixture of iohexol and saline). This was done under general anesthesia by an intramuscular administration of alfaxalone 2.5 mg/kg, medetomidine 40 μg/kg, and butorphanol 0.4 mg/kg, with a 7-day washout period between each treatment. The diluted contrast medium was distributed in the nasal cavity, external nares, and/or oral cavity in all rabbits receiving each treatment. The intranasal distribution volumes of the contrast medium were 287 (250-333) mm 3 [median (interquartile range)] for 0.15 ml, 433 (243-555) mm 3 for 0.3 ml, 552 (356-797) mm 3 for 0.45 ml, and 529 (356-722) mm 3 for 0.6 ml of treatment. The intranasal distribution volume for 0.15 ml treatment tended to be lower than that for 0.6 ml treatment (P = 0.083).The contrast medium was deposited in the trachea in one rabbit (12.5%) and four rabbits (50%) receiving treatments of 0.45 and 0.6 ml per nostril, respectively. The maximum volume of nasal atomization without aspiration into the trachea was 0.3 ml per nostril for the JW rabbits.

To prevent aspiration in Japanese White (JW) rabbits, the maximum single volume of medetomidine administered intranasally is 0.3 mL per nostril using a mucosal atomization device (MAD). This study aimed to examine the sedative effect of intranasal administration of medetomidine using MAD in eight healthy female JW rabbits. Each rabbit received intranasal atomization (INA) of saline (Control treatment) along with three doses of 1 mg/mL medetomidine (0.3 mL to one nostril [MED0.3 treatment]; 0.3 mL each to both nostrils [MED0.6 treatment]; 0.3 mL twice to both nostrils [MED1.2 treatment]), with a washout period of at least 7 days between treatments. The actual doses of medetomidine were 82 (75-84) μg/kg (median [interquartile range]), 163 (156-168) μg/kg, and 323 (295-343) μg/kg for the MED0.3, MED0.6, and MED1.2 treatments, respectively. A medetomidine-dose dependent sedative effect was detected, and the loss of righting reflex (LRR) was achieved in one rabbit at 18 min, seven rabbits at 11 (9-18) min, and eight rabbits at 7 (4-18) min after the MED0.3, MED0.6, and MED1.2 treatments, respectively. The LRR was maintained for 63 (29-71) min and 83 (68-101) min after the MED0.6 and MED1.2 treatments, respectively. Additionally, the INA of medetomidine produced a significant dose-dependent cardiorespiratory depression including a decrease in pulse rate, respiratory rate, percutaneous oxygen saturation, and arterial partial pressure of oxygen, and an increase in arterial partial pressure of carbon dioxide in the rabbits.

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