Reversal of ketamine/xylazine anesthesia in the rabbit with yohimbine.

Ketamine and xylazine used in combination have been shown to be effective, easily administered, cost efficient agents for surgical anesthesia in the rabbit. The effect of xylazine on the central nervous system has been shown to be mediated through alpha-2 adrenergic receptors. Yohimbine, an alpha-2 adrenergic antagonist has been shown to reverse xylazine induced depression and partially antagonize ketamine in other species. We evaluated the antagonistic effect of yohimbine on ketamine/xylazine anesthesia in the rabbit. Six New Zealand White rabbits were anesthetized with intramuscular ketamine (50 mg/kg) and xylazine (10 mg/kg) to establish baseline parameters including respiratory rate, heart rate, and palpebral, pedal and postural reflex activity. Fourteen days later each rabbit was subjected to the same anesthetic regimen followed 30 minutes later by the intravenous administration of yohimbine (0.2 mg/kg). The duration of anesthesia estimated by the time elapsed between the loss and return of the palpebral reflex was reduced in the yohimbine treated trial (means = 29.7 +/- 1.9 minutes) compared to the control trial (means = 67.0 +/- 13.5 minutes). The palpebral reflex returned within 5 minutes following yohimbine treatment. Our results indicated that yohimbine is an effective antagonist of ketamine/xylazine anesthesia in the rabbit. Yohimbine decreases anesthetic duration after intravenous administration and also may aid in the control of undesirable anesthetic effects and overdosage.